4. Evolution in Stem Group Angiosperms.
5. Relationships between Extant Angiosperms.
6. Cretaceous History of Angiosperms.
8. Flowers, Pollination, and Evolution. 9. The Physiological-Ecological Context of Angiosperm Evolution. When thinking about evolution in general, a well-supported phylogeny is of course a sine qua non. Beyond this, there are important issues of dating, understanding fossils, working out diversification rates, optimising characters on trees, etc., that need to be taken into consideration. I discuss some of these issues briefly below, but please consult the primary literature for details; see also Freckleton (2009). 1. Dating is critical, but how to do this remains a subject of intense discussion (e.g. Magallón and Sanderson 2001; Graur & Martin 2003; Pirie et al. 2005; Renner 2005b; Bell & Donoghue 2005; Magallón & Sanderson 2005; Rutschmann et al. 2007; Sanderson et al. 2004; H. Wang et al. 2009; Smith et al. 2010: molecular dating; Crepet et al. 2004: palaeontological dating; Magallón 2009; Milne 2009: sampling; Burleigh 2012; especially Sauquet et al. 2012). Many clade ages are not very reliable at this stage of our knowledge, and in several cases there are wildly different estimates for the same event. For instance, compare Wikström et al. (2001, 2004), Davies et al. (2004) and Clarke et al. (2011) for angiosperm ages, the latter suggest an origin in the Jurassic or earlier. See also Sauquet et al. (2012) for Nothofagus, Crisp and Cook (2011) and Martínez et al. (2012) for cycads, and Barreda et al. (2010b, 2012) and Heads (2012) for Asteraceae (Waters et al. 2013 briefly critiqued the distinctive approach followed by Heads and some others). Although many ages for clades are given on these pages, they should all be treated with extreme caution. Dates based on molecular, tectonic, and paleontological data can be in conflict, and the first two may give substantially older ages than the laast. Of course, fossils yield only a minimum age (Donoghue & Benton 2007), and fragmentary fossils in particular may be assignable to more than one node. The identification of fossils and their selection for calibration of molecular trees should be treated very carefully (e.g. Gandolfo et al. 2004; Graham 2010; Clarke et al. 2011; etc); in a study of different ways of calibrating, and two different ways of dating, Sauquet et al. (2011) found that the ranges of the means alone for each node varied by up to a factor of 10 (see also Parham et al. 2011). The relaxed ages given by Magallón and Castillo (2009) are often substantially older than the constrained ages - for example, the relaxed crown group age for angiosperms is about 242 m.y., and the constrained age about 130 m.y. 2. Fossil evidence is of course central to understanding angiosperm evolution (see also 5 below). However, as with dating, one has a sense of unease, and some studies have questioned what had previously seemed to be quite well established fossil identifications (e.g. Cook & Crisp 2005; Nothofagus; Biffin et al. 2010b: Araucariaceae). In groups like Poaceae (Poinar 2004: see below, also Poaceae) there are amber fossils originally dated to 110-100 m.y.a., more recently to ca 98.8 m.y. (Shi et al. 2012), from the Cretaceous of Myanmar/Burma that suggest a substantially greater age for the clade and its diversification than is given by other dating methods. They would change many other dates for flowering plant clades and cause a general rethinking of angiosperm evolution; Poinar (2011) recently reaffirmed the probable identity of this fossil as Poaceae-Pooideae. Moreover, other core eudicot angiosperm fossils have been found in these amber deposits (e.g. Poinar 2011, Poinar et al. 2007, 2008), so much hangs on their correct dating (and identification). The fossil record is sure to have more surprises, and the recent discovery of Leefructus from early Cretaceous deposits 125.8-122.6 m.y. old and assigned to stem Ranunculaceae (Sun et al. 2011) will, if confirmed, also challenge many of our current ideas of angiosperm evolution. This raises the issue of the correct identification of fossil remains, which are nearly always more or less incomplete and so lacking critical features. To the extent that many fossils are stem-group members, they may lack distinctive features of the crown group. At the same time, they cannot be expected to be simply "ancestral", rather, they may have evolved distinctive features of their own, but these, given the nature of seed plant evolution, may well be parallelisms, so perhaps suggesting links with unrelated groups... 3. Distributions are not easy to interpret, since there is abundant evidence that the present and past distributions of many plants and animals are very different. Early in the Tertiary the distributions of a number of tropical taxa like Nypa and Cyclanthaceae that are today rather restricted were much wider (e.g. Plaziat et al 2001; Smith et al. 2008), while in the Oligocene humming birds were flying about in Europe (Mayr 2004). Genera and families continue to be added to this list (e.g. Stull et al. 2012; Manchester et al. 2012), and it is well known that many taxa now restricted to Southeast Asia grew in Europe and North America at various times in the Tertiary (e.g. Ferguson et al. 1997; Manchester et al. 2009).
Dates are of course essential when interpreting distributional patterns. In a number of clades, patterns that that seemed to reflect vicariance caused by plate tectonic events may be better explained by much more recent dispersal/migration events (e.g. Renner 2005b, de Queiroz 2005, Wen & Ickert-Bond 2009: summaries, also Higgins et al. 2003; Nathan 2006; Yoder & Nowak 2996; Carpenter et al. 2010; Gillespie et al. 2012a; Baker & Couvreur 2012a, b; Christenhusz & Chase 2012; c.f. in part Ladiges & Cantrill 2007; Heads 2008, etc.). Even Lars Brundin's hitherto iconic chironimid midge drift-determined distributions may need reinterpretation from this point of view (Krosch et al. 2011). For how organisms achieve the ranges that they have, about which we know little, see e.g. Schurr et al. (2009) and individual family accounts. 4. The apparently simple issue of species numbers is in fact not that straightforward. We have to be very careful even when discussing the size of extant clades. There are two aspects to this - what is really the clade of interest?, and, how many species does it contain? A. Orchidaceae are often considered to be a highly diverse clade, at least in terms of numbers of species, but since they are sister to the rest of the Asparagales, the disparity in species number, although considerable, is only three-fold (ca 22,000 vs. 7,100: note Sargent 2004 compared Orchidaceae with Hypoxidaceae). By some measures Asparagales minus Orchidaceae could be considered vegetatively and even florally more diverse than Orchidaceae, although it is very hard to compare morphological diversity. Furthermore, Asparagales, with ca 29,000 species, are sister to commelinids, with some 23,500 or more species, while within Orchidaceae most species are found in the largely epiphytic Epidendroideae (e.g. Gravendeel et al. 2004). So the related questions, "Are orchids really diverse, and if so, why?", are not easy to answer. Perhaps Epidendroideae, or a clade within them, is the hyperdiverse group. There are many other examples of extreme clade size imbalance throughout the tree. I take it as axiomatic that comparisons between taxa simply because they have the same hierarchical rank are usually ill-advised, putting it mildly. Simplistic "major clade"-type comparisons are not enough (Smith et al. 2011, but see Ricotta et al. 2012). B. Estimates of the number of extant species of flowering plants vary by a factor of about two - 422,127 (Govaerts 2001) to 223,300 (Scotland & Wortley 2003) - and perhaps add 20% (Joppa et al. 2010). 5. The relationships of angiosperms to other seed plants remain unclear (see below), and thus so do the whens, whys and hows of their initial diversification (see Davies et al. 2004b; Friis et al. 2005; Frohlich & Chase 2007; Pennisi 2009; Lee et al. 2011). Here we can distinguish between the origin of the clade of which
angiosperms are the only extant representative, i.e. stem angiosperms ("origin 1"), the origin of plants with carpels, tepals, and a heterosporangiate
strobilus, i.e. the evolution of plants with flowers ("origin 2"), and finally, the origin of crown angiosperms, i.e. the clade represented by the immediate common ancestor of extant flowering plants ("origin 3"). Stem angiosperms presumably are
of early Carboniferous age or even older, 350±35-305-275±35 m.y. old, if the angiosperm clade is sister to the clade including all living gymnosperms (e.g. Savard et al. 1994; Crane et al. 1995;
Crane 1999; Magallón & Castillo 2009; Clarke et al. 2011), perhaps to a younger bound of Permian in age (Doyle 1998a). Even if crown angiosperms are as much as 270 to 182 m.y. old in age (Smith et al. 2010), they still have a substantial stem history. For the bulk of their some 100 m.y. plus history plants along the angiosperm stem may well have had naked seeds and other features of extant gymnosperms. Although current evidence suggests that extant gymnosperms are monophyletic, when considering both extant and fossil taxa gymnosperms are paraphyletic with respect to angiosperms; angiosperms are derived from a gymnospermous ancestor. Little progress has been made in identifiying plants that can be placed somewhere between origin 1 and 3 over the last thirty years or more (Doyle 2012; c.f. X. Wang & Wang 2010; see Mathews & Kramer 2012 for a way forward). 6. Many characters seem to come and go on the tree almost willy-nilly, which makes their optimisation a distinctly hazardous undertaking. Thus using either parsimony or maximum likelihood, making apparently reasonable assumptions about weighting gains over losses (or vice versa), or just using the rather simple models of evolution explicit in ACCTRAN or DELTRAN to place the character on the tree (e.g. Donoghue & Ackerley 1996; Cunningham et al. 1998; Omland 1997, 1999; Ree & Donoghue 1999; Polly 2001; Webster & Purvis 2001; Ronquist 2004; Crisp & Cook 2005; O'Meara 2012), may greatly affect the position of
synapomorphies on trees, and hence our ideas of evolution (see e.g. Sannier et al. 2007; Sannier et al. 2011). Syme and Oakley (2012) suggest that tree-based and node-based methods give very different results when it comes to allowing reversals. 7. Understanding the palaeoecological context of the evolution of angiosperms is a challenge. Seed plant morphology and physiology and their interactions with the environment s.l. have shaped stem- and crown-angiosperm diversification since the Permian. However, ecological contexts change over time, so that of the early Tertiary diversification of angiosperms is likely to be quite different from those of the origins of stem- and crown-group angiosperms. The Tertiary context is perhaps initially connected with or shaped by the bolide impact at the K/T boundary, although much of angiosperm diversity as we now appreciate it seems to be a phenomenon of the later Tertiary, and again the ecological context has changed. Palaeontologists face this problem on a daily basis. Thus Rothwell et al. (2000) reconstructed the palaeoecology of the small, probably short-lived conifer Aethophyllum using a combination of evidence from the fossil, the palaeoenvironment, etc. (also e.g. Strömberg 2006). Although is tempting to read the ecology of early angiosperms from that of extant taxa of the ANITA grade, this is hazardous (e.g. Wheeler & Baas 1991, 1993; Philippe et al. 2008); however, if immediate relatives of angiosperms are unknown, working out how the ancestral angiosperm functioned will tend to be a top-down process (Feild & Arens 2005, 2007). Little et al. (2010) challenge the reliability of aspects of leaf morphology, especially the presence of teeth, as palaeoclimatic indicators. Furthermore, most angiosperms are symbiotic systems at a variety of levels. Features ascribed to plants may well be the result of interactions between plants, fungi, and/or bacteria (Friesen et al. 2011), and this goes far beyond the ancient endosymbiotic events that resulted in chloroplasts and mitochondria. Importantly, basic angiosperm physiology is mediated by fungi and bacteria both in the soil and in the plant, and this shaped and continues to shape both the local and the global environments. 8. With time, the tree, distributions, apomorphies, and numbers of species, we can begin to think about diversification. Although diversification is mentioned frequently below, both it and the related term, adaptive radiation, are imprecise and can be difficult to estimate and interpret (e.g. Bengtsson 1998; Sanderson 1998; Davies et al. 2004; Ricklefs 2007; Olson & Arroyo-Santos 2009; Ackerly 2009; Wertheim & Sanderson 2010; Stadler 2011a, b; Drummond et al. 2012, etc.). In curves showing diversity in clades over time, what can seem like an abrupt radiation, with rapid diversification after a period when there was little apparent diversity - the "broom and handle" and "stemmy" patterns evident in many clades - may be the result of extinction, diversification after the extinction event resuming at a rate similar to that before the event even if the overall appearance of the tree is that of a radiation (Crisp & Cook 2009). Extensive sampling (>80%) is needed if accurate estimates of slowdowns in diversification are to be made (Cusimano & Renner 2010), while diversification rates will automatically tend to increase towards the present. Simple experiments estimating future extinctions showed that these might affect estimates of imbalances of clade size at nodes of some 50 m.y. age (Clarke et al. 2011). In general, estimating clade imbalance is a remarkably tricky operation, especially in the near absence of fossils, the usual situation (Tarver & Donoghue 2011; see also e.g. Rabowsky 2010a, b). Even when there is an excellent fossil record, strategies like removing recently-radiating clades may be needed if one is to detect diversity loss in other clades (Morlon et al. 2011: whales, etc., see also Stadler 2011b). Furthermore, diversity/species numbers make up just one way to measure success, and I also think about other measures, such as dominance, biomass production and net primary productivity, below.. Associations between plants and insects may be close, whether the insects are herbivores, detritivores, or pollinators. The diversification of angiosperms appears to be broadly contemporaneous with the massive diversification of many insect groups that are now more or less dependent on them, although there is some argument as to just how closely linked the two were. Ehrlich and Raven (1964) provide an early statement of the idea of co-evolution; also see/c.f. Janzen 1980; Schemske 1983; Brouat et al. 2001; Futuyma & Agrawal 2009; Kato et al. 2010; Fordyce 2010; Janz 2011; de Vienne 2013 and others). Co-evolution can include anything from strict co-evolution in which changes in one member of the association is linked to changes in the other (cospeciation need not be involved), to cospeciation (which may not involve mutual evolutionary change), to key innovations and adaptive radiation. The reciprocal evolutionary change and diversification of co-evolving plant and animal groups seems to be quite uncommon, and usually involves vertical inheritance of parasites/endophytes (de Vienne et al. 2013), although there is quite close coevolution in some examples of herbivory and parasitisim (Winkler & Mitter 2008; Althoff et al. 2012, but c.f. some bruchids, etc.). Host switching is often associated with radiation of the insect on the new host (Fordyce 2010) and is probably common (de Vienne et al. 2013). Complicating our understanding of the interactions of insects and plants are the symbiotic bacteria associated with some insects, e.g. aphids (Frago et al. 2012). 2A. Insects and Herbivory. Details of plant-insect relationships are discussed after individual orders and families. Plants have evolved mechanical and especially chemical defences against herbivory, and some insects have evolved ways of tolerating these defences - or even eat only plants with particular defences that they then coopt for their own defence (e.g. Termonia et al. 2001 for chrysomelid leaf beetles). Plant tissues are, however, for the most part rather nutrient-poor, and plants cell walls are made up of the rather indigestible cellulose and still more indigestible lignin. However, many insects, and some other arthropods, are able to break down cellulose walls independent of any mutualistic association with microorganisms, as are well-known to occur in termites, which has interesting implications for the evolution of land plants and rheir associated insects (Calderón-Cortés et al. 2012 for a summary of the literature). Some plant and insect groups are rather closely associated, and one question is, to what extent is the evolution of the two connected? What attracts an egg-depositing insect to one plant and prevents it laying eggs on another is often some aspect of plant chemistry (see Bernays & Chapman 1995 and Fernandez & Hilker 2007 [Chrysomelidae] for host plant selection). In general, more related plants do have more similar animals eating them (Weiblen et al. 2006; Futuyma & Agrawal 2009 for literature), simply because they will tend to taste similarly. In any one local area, related plants may show greater than expected diversity of traits involved in herbivore defence (e.g. Becerra 2007; Becerra et al. 2009; Kursar et al. 2009). Some herbivorous insects effectively track plant secondary metabolites and are found on whatever plant has a particular metabolite, independent of the phylogeny of the plant groups concerned (e.g. Winkler et al. 2009). Glucosinolates and some alkaloids are examples; glucosinolates are found in both Putranjivaceae and Brassicales, as are the pierid butterflies that are attracted to glucosinolates, while swallowtail butterflies are found on Rutaceae and Lauraceae, the two having similar alkaloids. Herbivorous insects may sequester secondary metabolites from the plant in the larva and/or adult stages, ensuring some measure of protection by so doing and often having a warning colouration (i.e., they are aposematic), or they may use plant metabolites for pheromones to attract mates, or these metabolites may simply act as oviposition cues, not being otherwise utilised by the insect (Brower & Brower 1964 on butterflies; Nishida 2002 for a review). Protective metabolites may be found in latex, or they may be translocated via the vascular tissue, or there may be other specialised tissues involved. Herbivorous insects that eat plants with such defences may show distinctive veing-cutting behaviours which stop the supply of any protectants to the plant tissue and enables the insect to eat it (see e.g. Dussourd & Eisner 1987; McCloud et al. 1995; Becerra et al. 2001; Dussourd 2009). Within herbivores, there is a general decrease in host specificity both in temperate and tropical regions that follows the sequence: granivores > leaf miners > fructivores > leaf chewers = sap suckers > wood eaters > root feeders (Novotny & Basset 2005), Specialization in weevil-plant associations is similar: fruit and seed > wood > root and stem eaters (McKenna et al. 2009). How insect larvae feed, i.e., whether they are internal feeders like stem borers and whether they can tolerate raphides, or latex, etc., may be more conserved than associations between larvae and particular groups of plants or other types of feeding behaviours (e.g. Powell 1980; Peigler 1986; Powell et al. 1999: associations with latex-containing plants; Konno 2011: chemistry; Farrell & Sequiera 2001; Lopez-Vaamonde et al. 2003, 2006). Phylogenetic conservatism may be greater in groups in which the adults tend to remain close to plants in which they grew up, as with beetles, compared to the situation where the adult may fly away, as in many lepidoptera (Berenbaum & Passoa 1999). Plant-feeding insects make up at least one quarter of all described species, and over half the beetles (Janz et al. 2006; Farrell 1998: ca one third of beetles, Hunt et al. 2007), although there are also very species-rich beetle clades that are neither herbivores nor decomposers (e.g. Barraclough et al. 1998). Clades of phytophagous insects may be more speciose that their non-phytophagous sister groups, ectophagous clades more diverse than their endophagous sister taxa, phytophagous clades more diverse than non-phytophagous, and clades that eat angiosperms more speciose compared to those that eat other plants (Mitter et al. 1988; Winkler & Mitter 2008). For a comprehensive phylogeny of all beetles, see Hunt et al. (2007; c.f. Farrell 1998). Since there seems to be no strong association of diversification and the adoption of herbivory, or between shifts from gymnosperms to angiosperms as a food source, and also because over 100 extant insect lineages had diverged before the beginning of the Cretaceous, insect and angiosperm evolution seem not to be tightly linked (Hunt et al. 2007). Weevils are a particularly diverse group with some 62,000 species described, but perhaps 220,000+ species altogether. McKenna et al. (2009) suggest that crown-group diversification of major angiosperm-associated weevil clades was underway by the Aptian 125-112 m.y.a., and there was a "massive diversification" as angiosperms became floristically common. "Basal" Curculionidae show strong associations with monocots, but there is little evidence that early monocots were either particularly abundant or ecologically successful (Crane et al. 1995; Friis et al. 2004; J. A. Doyle et al. 2008; c.f. McKenna et al. 2009). Bark beetles are weevils that are decomposers; they are less speciose in clades that returned to conifers. Scolytinae and Platypodinae include the ambrosia beetles; parental care is almost universal here, and the weevils make tunnels in the wood and are associated with the ambrosia fungi (Ophiostoma, Ceratocystis: Ophiostomatales, ascomycetes). This association has evolved about seven times in these and related weevils and is unreversed (e.g. Farrell et al. 2001; Jordal et al. 2011). Scolytinae, Cossoninae, and Platypodinae are the three major clades of wood-boring (endophagous) weevils, a habit that originated independently in the three (Haran et al. 2013). Chrysomelidae or leaf beetles, including the bruchids or seed beetles, are another very speciose herbivorous clade. Their origin has been dated to (86-)79-73(-63) m.y.a., well after the origin of the angiosperms (e.g. Gómez-Zurita et al. 2007). There are at least 150,000 species of butterflies and moths (Lepidoptera) (Roe et al. 2009 for a summary), and larvae of about two thirds of these are herbivores, most being mono- or oligophagous (Bernays & Chapman 1994). Cho et al. (2011 and literature; see also Mutanen et al. 2010) suggest that butterflies and moths are not sister groups, the butterfly clade also includes a small clade made up of the mostly night-flying Hedylidae, the American moth-butterflies, but relationships among major groups of ditrysian insects - ditrysia also include the majority of moths, both macro- and microlepidoptera - are unclear (Mutanen et al. 2010). Relationships among butterflies s.l. may be [Papilionidae [[Hedylidae + Hesperidiidae] [Nymphalidae [Pieridae [Riodinidae + Lycaenidae]]]]], although the position of Pieridae is unclear (Heikkilä et al. 2011). Grimaldi (1999) suggested that diversification of the clades with probosces began in the mid- to upper Jurassic; Labandeira et al. (1997) suggested somewhat older dates. There are over 4,000 species of aphids (Aphididae - hemipterans) feeding on plant sap; again, diversification was Late Cretaceous/early Tertiary (von Dohlen & Moran 2000). Ants, almost 12,000 species, also seem to have diversified in the late Cretaceous-early Eocene, 75-50 m.y.a. Another set of close associations between plant and insect results in distinctive galls (see Redfern 2011 for a good introduction). There are anywhere from (21,000-)132,930(-211,000) species of of galling insects, the estimates partly depending on the numbers of flowering plants accepted because of the specificity of many gall insect/plant associations. Cecidomyiidae (dipterans, gall midges), the largest group of galling insects and comprising perhaps 25% of galling insects in North America (Abrahamson & Weiss 1997), are worldwide in distribution but show no particular patterns of host associations (Yukawa & Rohfritsch 2005: but see below for geography), while Cynipidae (hymenopterans, gall wasps) may comprise as many as 50% of gallers and are north temperate. Smaller groups include psyllids (jumping plant lice, hemipterans) which are particularly common in Australia (Fernandes & Price 1991; Crespi et al. 2004; Espiritó-Santo & Fernandes 2007; Raman et al. 2005); some aphids and other insects are also gallers. In general, gall-inducing insects are commonest on sclerophyllous plants growing on poor soils in warm climates between 25 and 45o N and S, or perhaps more generally in species-rich communities, whether dry or wet, but not necessarily in tropical climates (Price et al. 1998; Yukawa & Rohfritsch 2005; see Price et al. 1987 for galling in an adaptive context). Other organisms may be directly involved in the establishment of galls, such as fungi in cecidomyid ambrosia galls (Rohritsch 2009 and references), and a whole network of parasites, hyperparasites and predators is all more or less dependent on gall larvae (Redfern 2011). Extant angiosperms show a correlation between woodiness and tannin frequency and a negative correlation between tannins (generalized defence) frequency and alkaloid and other secondary metabolites (specific defence) frequencies. It was suggested that plants that were obvious or apparent to herbivores had the first kind of defence, more short-lived plants the second (e.g. Feeney 1976; Silvertown & Dodd 1996; see also Levin 1976; Mole 1993). Plants might have "qualitative" and "quantitative" defences. In the first, defensive compounds are highly toxic and butterfly groups like Nymphalidae are specialized herbivores, in the second, defences are more generalised - polyphenolics and the like - and groups like Lycaenidae are the herbivores (Fielder 1996). Plants that were not apparent would need defences only against generalist herbivores (Endara & Coley 2011). However, the nature and amount of the defensive compounds produced can also be explained, and perhaps more satifactorily, by the resource availability hypothesis, in which herbivore defence is thought of from a cost:benefit point of view (Endara & Coley 2011 for a summary). Qualitative defences are often linked with low concentrations of available nutrients (Coley et al. 1985). in particular, the growth rate of the plant affects the nature and amount of defences laid down, fast-growing plants needing less in the way of defence since their leaves are short-lived and would soon be replaced even if they had not been eaten (Endara & Coley 2011). Deciduous plants in general, with their rather thin leaves, tend to be eaten by insects more than plants with long-lived xeromorphic leaves (e.g. Coley & Barone 1996; Arnold et al. 2001; Wilf et al. 2001; Lewinsohn et al. 2005). There is much discussion about possible correlations between geography, species richness, herbivory and defensive metabolites. In general, herbivory is supposed to be greater in tropical than in temperate forests, and defences should be disposed likewise (Adams et al. 2011 and references; see also Agrawal et al. 2012). However, two recent comprehensive analyses suggest the reverse, that both herbivory and allocation of resources to plant defences tend to be greater at higher latitudes (Moles et al. 2011a, b), while Salazar and Marquis (2012) noted that although the diversity of herbivores on Piper increased towards the equator, the amount of herbivory did not. Novotny et al. (2006) suggested that individual species of temperate and tropical plants (controlled for phylogenetic relationships) support a similar number of insect species, but since there were many more species of plants in the tropics, there would be many more species of insects there. However, there may be other patterns of association (c.f. Novotny et al. 2007 and Dyer et al. 2007), and an analysis of the food plants of Californian butterflies showed plant and butterfly diversity to be at most weakly correlated, whether the caterpillars had broad or narrow host plant preferences (Hawkins & Porter 2002). To sumarize: The impact of insect/plant associations on plant diversification is still poorly understood (Futuyma and Agrawal 2009: also other papers in Proc. National Acad. Sci. U.S.A. 106(43)). In addition, symbionts, particularly bacteria, may be common in the insect, and this may affect its interaction with the plant (Frago et al. 2012). In some cases, diversification of plants can be linked to the development of particular defences, but this does not happen in any simple fashion; the mechanism by which insect diversification increases when feeding on angiosperms is also unclear (Janz 2011). However, a recent idea is to apply the ideas of island biogeography to the problem. With cecidomyiid gallers, at least, if host species are closer, insect diversity may go up because it is easier to switch hosts, and if ranges of insects are large and the plants are structurally complex, diversity also increases; clade age has little to do with it (Joy & Crespi 2012; for age, c.f. Brändle & Brandl 2002 [in part]; Farrell & Mitter 1994). We need to know more about both the timing of diversification and patterns of phylogenetic relationships in both groups, and evidence for the former in particular is often lacking (de Vienne et al. 2013), worse, there is uncertainty in both areas; this is discused further below. 2B. Insects as Pollinators. There is much debate over flower-insect co-evolution, the existence of wide-ranging pollination syndromes versus sometimes quite local guilds (Johnson 2010), and what exactly pollinators might see and respond to (Waser et al. 1996; Chittka et al. 1999; Fenster et al. 2004; Waser & Ollerton 2006; Raguso 2008; Ollerton et al. 2009a). Rodríguez et al. (2004) and Horridge (2009) discuss the bee's point of view, the former, thinking about monosymmetry in particular, the latter more generally. Another strand of the discussion is the idea that pollination is the exploitation of pre-existing perceptual/sensory biases of the pollinator by the plant (e.g. Chittka 1996; Schaefer & Ruxton 2009, 2010; Schiestl 2010; Schiestl et al. 2010; Schiestl & Dötterl 2012), in which case it becomes difficult to maintain other than general ideas of co-evolution of plant and pollinator, let alone those of co-speciation. Evolution is probably asymmetrical, occuring more in plants. See Barth (1985) for a readable account of the relationships between insects and flowers. For the evolution of butterflies and moths, see above. The evolution of bees is of particular importance, given the close involvement of many of them with angiosperm pollination (for bees and pollen, see Westerkamp 1996; for an account of all bee groups, see Michener 2007). Apoidea includes the sphecoid wasps, since bees evolved from within the wasps, a group that feeds their larvae with insects. The basic phylogenetic structure within Anthophila/Apiformes, the group that includes all bees, is [Dasypodainae [[Meganomiinae + Melittinae] [[Andrenidae [Halictidae [Stenotritidae + Colletidae]]] [Apidae + Megachilidae]]]] (Cardinal & Danforth 2013), i.e. the old mellitids, here represented by Dasypodainae and [Meganomiinae + Melittinae], are paraphyletic. Recent suggestions are that the age of stem-group bees is some (182-)149(-119) m.y., in line with some revisions of ages for the origin of angiosperms, with crown-group Megachilidae, a major clade including the leaf-cutting bees, starting to diversify (154-)126(-100) m.y.a. (HPD: Litman et al. 2011). Similarly, the age of crown-group bees is estimated at (132-)123(-113) m.y. (Cardinal & Danforth 2013), all bee families having diverged by the K/T boundary. Other estimates for stem Apidae are some 135-120 m.y.a. (Grimaldi & Engel 2005), with their initial diversification in the early to mid Cretaceous 112-100 m.y. occurring in association with the evolution of angiosperms (Grimaldi 1999, see also Engel 2000; Michez et al. 2009, 2012: discussion of fossils purporting to be bees; Grimaldi & Engel 2005; Almeida & Danforth 2009; c.f. Renner & Schaefer 2010). Within Apidae, the somewhat over 1,000 species of at least primitively eusocial corbiculate bees, relationships are [[Euglossini + Apini] [Meliponini + Bombini]] (Cameron 2004: morphology and behaviour-based trees conflict with those based on molecular data, the latter give the relationships above; also Cardinal et al. 2010; Cardinal & Danforth 2011; Danforth et al. 2013). Crown-group corbiculate bees are dated to (95-)87(-78) m.y. (Cardinal & Danforth 2011). The crown group of the stingless, highly eusocial meliponines are dated to (61-)58(-56) m.y., that of orchid bees (euglossines), (35-)28(-21) m.y., bumble bees (Bombini), (31-)21(-12) m.y., and of honey bees (30-)22(-16) m.y. (Cardinal & Danforth 2011). Another estimate of crown group euglossine diversification is 42-27 m.y. (Ramírez et al. 2010).
These general relationships are consistent with the appearance of bees in the fossil record. The earliest fossil bee, perhaps sister to other Apoidea, was found in amber of Upper Albian (probably Early Cenomanian, (99.4-)98.8(-98.2) m.y. - Shi et al. 2012) from Burma (Poinar & Danforth 2006); it is also quite small, being ca 5 mm long, in line with the often rather small Cretaceous flowers. However, this insect may not be a bee, rather, some kind of predatory wasp (Ohl & Engel 2007). A younger fossil from the New Jersey amber of the Late Cretaceous (96-74 m.y.a.) was assigned to the extant genus Trigona, a highly derived eusocial stingless bee (Apidae - Meliponini: Michener & Grimaldi 1988); both its age (now estimated at 70-65 m.y.) and its relationships - it is now placed in Cretotrigona, and is a crown of stem meliponine - have been re-evaluated (Engel 2000). Both Apidae and Megachilidae, derived, long-tongued bees, are known from Baltic amber of Eocene age (Danforth et al. 2006 and references). Note that colour perception is not an apomorphy for bees (Chittka 1996). Close relationships between seed plants and fungi, whether as mycorrhizae or endophytes, are ubiquitous. The evolution and ecological significance of mycorrhizae have been widely discussed (see Malloch et al. 1980; papers in Allen 1992; Read et al. 2000; Landis et al. 2002; Egger & Hibbett 2004; Taylor et al. 2009, etc.), as has the morphology of the plant/fungus interface (e.g. Peterson & Massicotte 2004; Peterson 2013 and references) and how the fungus uses the 10% or more of photosynthesate that it gets from the plant (Leake et al. 2004). Being mycorrhizal is not a simple either/or matter, and the one species of plant may have a variety of associations with fungi, and the distinctions between some of the mycorrhizal (and endophyte) types that have been described can be questioned (Peterson 2013). Nevertheless, relatively few plants form both ecto- and endomycorrhizal associations (Poole & Sylvia 1990; Molina et al. 1992 for some examples), however, both Mucoromycotina and Glomeromycota can form mycorrhizal associatoons with gametophytes of the same species of hornworts (Desirò et al. 2013). Aquatic plants, hardly surprisingly, often lack mycorrhizae (see Safir 1987 and Radhika & Rodrigues 2007 and references for records; de Marins et al. 2009), but the frequent absence of mycorrhizae in Caryophyllales, Proteales, etc., is somewhat surprising. Epiphytic taxa are not often mycorrhizal (Janos 1993; see other papers in Mycorrhiza 4(1). 1994; Desirò et al. 2013), but c.f. Ericaceae, Orchidaceae (e.g. Kottke et al. 2008; Martos et al. 2012). Overall some 18% of flowering plants may lack mycorrhizae, and a further 12% are only facultatively mycorrhizal (Molina et al. 1992). For comprehensive surveys on mycorrhizal associations. see Brundrett (2008: updated online resource, 2009) and Akhmetzhanova et al. (2012) in particular. The development of mycorrhizae is linked to various aspects of root architecture - root thicknesss, root branching, the development of root hairs (Baylis 1975; Schweiger et al. 1995 and references) - as well as the nutrient status of the soil, and benefits accruing to the partners may be similarly labile (Newsham et al. 1995). Thus the development of root hairs or of a vesicular arbuscular mycorrhizal association (VAM) may be alternative ways in which the plant obtains phosphorous when it is in short supply (Schweiger et al. 1995 and references). Distinctive root morphologies like dauciform roots are additional responses of the plant to nutient-poor conditions (e.g. Schweiger et al. 1995; Playsted et al. 2006; Gao & Yang 2010). Endomycorrhizae or vesicular-arbuscular mycorrhizae (VAM) are very widespread. They are found in about 70% of seed plants, 80% of all plant species, 92% of plant families (Blackwell 2011). This association is probably of very long standing, and may even be a feature of the common ancestor of all land plants (see also Baylis 1975; Redecker et al. 2000b; Kottke & Nebel 2005; Duckett et al. 2006b; Ligrone et al. 2007; Parniske 2008; B. Wang et al. 2010). Just how many times VAM associations evolved in land plants is unclear. Complicating any simple story is the fact that fungi are associated with the gametophytic generation in liverworts and even in hornworts (Desirò et al. 2013) and the recent discovery of the involvement of Endogone-like fungi (Mucoromycotina) in mycorrhizae of some liverworts (Treubia) and of hornworts (Bidartondo et al. 2011). In the former group the association with Glomeromycota may even have been ancestral (Desirò et al. 2013). Embryophytes and fungi established associations very early in the Silurian/Devonian, initially with the gametophytes of the former (Selosse & Tacon 1998; Nebel et al. 2004), however, mosses in particular usually lack mycorrhizal associations (Read et al. 2000; Kottke & Nebel 2005; Duckett et al. 2006b; Ligrone et al. 2007; Wickett & Goffinet 2008; Stenroos et al. 2010; Pressel et al. 2008, 2010). Mycorrhizae have not often been found in fossil gymnosperms, but have recently been reported from Upper Permian Glossopteris (Harper et al. 2013). Glomeromycota are the fungi involved in VAM (Schüßler et al. 2001). Their hyphae are aseptate and intracellular, often forming vesicles or branching structures (the arbuscules) within the cells. There is substantial variation both in the morphological details of the fungus-plant association (e.g. Smith & Smith 1997; Peterson & Massicotte 2004) and in the proportion of fungal biomass inside and outside the plant, the latter depending on the group of Glomeromycota (Maherali & Klironomos 2007). Sexual reproduction is at most exceedingly uncommon, but the spores are multinucleate, the nuclei not having any obvious immediate common ancestor, so the unit of selection may be the individual nucleus (Jany & Pawlowska 2010). Hyphae from different mycelia can fuse, making the nuclear mix yet more complex (Giovannetti et al. 2004). Some 290 species of Glomeromycota have so far been described (Öpik et al. 2010; Merckx et al. 2012), and all form VAM. Although some are found on only a few plants, many plants form associations with several species, ecological specialists and generalists forming associations with different fungi (Öpik et al. 2009, 2010); there is some evidence for host specificity or at least host preferences (Gosling et al. 2013). A single plant can form different associations sequentially (van der Heijden et al. 2006) or unrelated species of plants may be colonized by the one fungus (Kottke et al. 2008; Walder et al. 2012). Recent surveys suggest both that dispersal of the fungi may be limited and also that the diversity of Glomeromycota has been considerably underestimated. However, although there may well be 1,000 or even many more species (Kivlin et al. 2011), that is still far fewer than the probably 200,000 species or so of plants colonized (Rinaldi et al. 2008). Extant forests made up of VAM trees are more diverse than forests with ectomycorrhizal trees (Malloch et al. 1980; McGuire 2007a), and the prevalence of VAM associations decreases with latitude (Olsson et al. 2004: c.f. other fungal associations). In VAM associations, nutrient uptake by the plant - especially of phosphorous, although recent work adds nitrogen - is increased, and water uptake is improved (Allen 1992; Govindarajulu et al. 2005; Leigh et al. 2009 and references; Tian et al. 2010; Bonfante & Genre 2010). Interestingly, Gosling et al. (2013) found that the diversity, but often not colonization rate, of VAM fungi was affected by the concentration of soil phosporous. Since a single fungus individual can be associated with more than one plant, and because hyphae from different individuals may fuse, a potentially quite large number of plants from the same or different species may be put in indirect contact with each other (Giovannetti et al. 2004), and so it becomes a very complex calculation to estimate the costs and benefits accruing to the parties involved (Walder et al. 2012). The mycorrhizae have substantial beneficial effects on soil structure (Taylor et al. 2009), improving drainage, and hence weathering, and also playing an important role in phosphorous uptake by scavenging for it more efficiently (S. E. Smith et al. 2011). The fungus obtains at least carbohydrates from the plant (Helber et al. 2011; see also Walder et al. 2012). How changing carbon dioxide concentrations in the atmosphere might affect the soil carbon storage activities of VAM is unclear (Verbruggen et al. 2012 and references). Maherali & Klironomos (2007) found that ecosystem functioning was improved if all three major types of Glomerophycota were in the one community. Although rather few of the details of plant-mycorrhizal interaction are known (Whitfield 2007), a number of genes involved in the establishment of VAM associations are the same as those involved in establishment of nodulation in the nitrogen-fixing clade (e.g. Maillet et al. 2010 and references, also the Fabales page). How the fungus invades plant tissue may be similar to the establishment of parasitism (Bonfante & Genre 2010). Initial attraction of the fungus to the plant, and also hyphal branching, may be mediated by strigolactones secreted by the root (Akiyama 2010 and references). These strigolactones may initially have been involved in rhizoid elongation (Delaux et al. 2012). Ectomycorrhizae (ECM) grow on many fewer species of plants. Estimates vary: 2,500-3,000 species (Smith & Read 2008), 5,600 species of angiosperms + 285 species of gymnosperms (Brundrett 2009), or ca 8,000 species (Rinaldi et al. 2008: gymnosperms included). There is a strong phylogenetic signal in the plants that form ECM associations (e.g. Alexander & Lee 2005), and this is discussed below. Many more species of fungi are involved in this association. Conservative estimates are 7,750 species of fungi, although the figure may be as high as 20,000-25,000 (Rinaldi et al. 2008), with tropical lowland ectomycorrhizal associations being as diverse as those in more temperate climes (Henkel et al. 2012: Dicymbe-Fabaceae; Brearley 2012: Dipterocarpaceae). Thus the relationship between numbers of species of plants and fungi is opposite to that in both VAM associations and perhaps also the modified ectomycorrhizal associations in Ericaceae (ERM) and Orchidaceae (Rinaldi et al. 2008: estimates for Ericaceae surely too low). Basidiomycetes are frequent ECM associates, but Pezizales (ascomycetes) are also quite common (Tedersoo et al. 2006: hypogeous fungi are derived from them), as in Ericaceae, although until the advent of molecular methods, detecting the fungi depended on their being cultivable. Although basidiomycetes of the Sebacinales-B group may form associations with both Ericaceae and Orchidaceae, different species are involved (Setaro et al. 2012). ECM hyphae form a Hartig net investing the rootlets and penetrating between the cortical cells; the hyphae are septate and are not intracellular except in Ericaceae and Orchidaceae. There are other variants, such as tuberculate mycorrhizae, clusters of roots surrounded by hyphae (Smith & Pfister 2009). ECM help in the aquisition of nitrogen and phosporous by the plant, obtaining them from material as diverse as pollen and dead nematodes and breaking down chitin; nitrogen is transferred to the plant in an organic form, e.g. as glutamine (Alexander 1989; Newbery et al. 1997; Michelsen et al. 1998; Read & Perez-Moreno 2003; Cairney & Meharg 2003; Lindahl & Taylor 2004; Martin & Nehls 2010; Bonfante & Genre 2010). ECM fungi may even retain nitrogen in their mycelium, perhaps especially when the supply of photosynthesate from the plant is high, but the result is soil with very low N concentrations that is unfavourable for the growth of non-ECM plants (Näsholm et al. 2013). There is probably an evolutionary sequence white rot -> brown rot -> ectomycorrhizae, with development of ECM associations being favoured by the ecological conditions (e.g. low nitrogen) that result from the activities of brown rot fungi (Eastwood et al. 2011; see also Floudas et al. 2012). Hibbett et al. (2000) suggested that white-rot fungi might also be derived from within ECM clades. White rot and brown rot fungi are widely scattered through Agaricomycota (Eastwood et al. 2011). A number of flowering plants are myco-heterotrophs, lacking chlorophyll and very largely depending on the activities of associated fungi for their nutrition; similar associations are also found in some gametophytes of free-sporing plants. For the taxonomically widespread associations between glomeromycotes and myco-heterotrophic plants, see Merckx et al. (2012); note that myco-heterotrophic Ericaceae and Orchidaceae have modified ECM-type associations (e.g. Perotto et al. 2012). Endophytic fungi, fungi growing inside plants, have been placed in four groups. Class one endophytes are clavicipitaceous fungi and occur in grasses with which they form very close associations (Schardl 2010). Other endophytes are often not Clavicipitaceae. Class two endophytes pervade all the tissues of the plant, although the fungi involved are not particularly speciose, while class three endophytes are restricted to shoots and are very diverse. Class four endophytes, dark septate endophytes, are restricted to roots (Rodriguez et al. 2009). Endophytic fungi of some sort or other are likely to be found in all seed plants (Rodriguez et al. 2009; Hoffman & Arnold 2010; Friesen et al. 2011), perhaps particularly in Poaceae and Ericaceae (e.g. Petrini 1986, other papers in this volume; Saikkonen et al. 2004); Herre et al. (2005) characterize tropical plants in particular as being chimaeras as a result. The number of species of endophytic fungi is likely to be very large indeed. For example, Arnold et al. (2001) found 418 morphospecies of class three endophytes in only 83 leaves of two species of tropical trees, Ouratea (Ochnaceae) and Heisteria (Erythropalaceae) (see also Bills & Polishook 1994; Frohlich & Hyde 1999; Arnold & Lutzoni 2007 and other articles in Ecology 88[3]. 2007). Similarly, several hundred species of fungi have been found in the phyllosphere, the above-ground surface of the plant (Jumpponen & Jones 2009). Gazis et al. (2012) even described a new class of ascomycete fungi based on endophytes growing in the sapwood of Peruvian Hevea. In other than class one endophytes, details of what the fungi are doing, let alone of any advantages accruing to the parties involved, are largely unclear (e.g. see Jumpponen 2001: dark septate endophytes; Jumpponen & Jones 2009: phyllosphere; Rodriguez et al. 2009: summary). Fungi may affect seed germination and survival (U'Ren et al. 2009), but again, details are lacking, and the fungi seem to be more related to pathogens and other endophytes than to saprotrophic fungi. Endophytic associations are probably at least intermittently mutualistic (Carroll 1988, 1995); they may often be involved in facilitating stress tolerance in plants (Rodriguez & Redman 2008). Van Bael et al. (2009) found that leaf-cutting ants seemed to dislike plants with numerous endophytes (nitrogen-fixing bacteria, esp. Klebsiella, are also an integral part of this system - Pinto-Tómas et al. 2009). They have also been implicated in the protection of the host plant against fungal pathogens (Martin et al. 2012: in vitro; Raghavendra & Newcombe 2012). Most endophytes are Ascomycota. Fungi living inside lichens, endolichenic fungi - these are different from the mycobionts that form the main association with algae that constitutes the lichen thallus - may be phylogenetically close to endophytic clades (Arnold et al. 2009b). Grass endophytes are perhaps derived from fungi that are insect pathogens, and some species of fungi are both pathogen and endophyte (Spatafora et al. 2007; Sasan & Bidochka 2012). Movement of nitrogen from caterpillars occupied by the ubiquitous insect pathogen Metarhizium (related to grass class 1 endophytes) to a grass (Panicum virgatum, switch grass, so not Poöideae) and legume (Phaseolus vulgaris, a bean) in which the fungus is also an endophyte has rcenetly been demonstrated (Behie et al. 2012). However, other fungal groups are involved. Sebacinales (basidiomycetes) are particularly diverse ecologically, being common endophytes (Weiß et al. 2009) as well as producing the distinctive mycorrhizae of Ericaceae and Orchidaceae. In general, transmission of endophytes may occur via the seed (vertical transmission), as is common in class one endophytes in particular, or via fungal spores (horizontal transmission), more common in other endophytic associations (Arnold 2008). Clear distinctions between different types of fungal associations can be hard to draw (Gao & Yang 2010; esp. Vrålstad 2004; Perotto et al. 2012), and the line between mutualism - or at least prolonged symbiosis - and parasitism is a fine one (Eaton et al. 2010 and references). At least some ECM fungi are very similar or identical to ERM fungi; both can be more or less saprotrophic and take up nitrogen in an organic form (e.g. Michelsen et al. 1996; Jonasson & Michelsen 1996; Hashimoto et al. 2012). Villareal-Ruiz et al. (2004) even persuaded a single fungal mycelium to form an ECM with Pinus sylvestris and an ERM with Vaccinium myrtillus) at the same time. Consistent with this idea, Vrålstad et al. (2002) and others have found fungal isolates from plants with ECM, ERM, and also dark septate endophytes to be more or less intermixed on phylogenetic trees and showing little phylogenetic divergence (see also Perotto et al. 2012). Consequently, Vrålstad (2004) suggested that ECM and ERM formed a single ecological guild, one of whose characteristics is the uptake of organic nitrogen by the plant (c.f. in part Lindahl et al. 2002: opposition between decomposer and mycorrhizal fungi; Talbot et al. 2008: VAM; Inselbacher et al. 2012). The fungal associates of Arbutus menziesii, from Pacific North America and which has arbutoid mycorrhizae, are diverse and occur on other angiosperms and in particular Pinaceae (Pseudotsuga) growing in the same area (Kennedy et al. 2012). As already mentioned, a single fungus may form mycorrhizal associations - in some cases, different kinds of mycorrhizae - with two or more species of plants simultaneously, so forming complex mycorrhizal networks (e.g. Villareal-Ruiz et al. 2004; Simard & Durall 2004; Selosse et al. 2007b; Kennedy et al. 2012). Thus liverwort gametophytes may form associations with fungi that are also ECM on the flowering plant on which the liverwort is found. Examples include Marchantia/mycorrhizal fungus/Podocarpus and the mycoheterotrophic chlorophyll-less Cryptothallus/the basidiomycete Tulasnella/Pinus-Betula (Read et al. 2000; Bidartondo et al. 2003; Kottke & Nebel 2005 and references). The ascomycete Rhizoscyphus ericae is often an ERM on the hair roots of north temperate Ericaceae, it can also be an ECM on Pinus growing together with these Ericaceae (Grelet et al. 2010; see also Villarreal-Ruiz et al. 2004), and it also forms mycorrhizal associations with Jungermanniales-Schistochilaceae, leafy liverworts (Pressel et al. 2008). Weiß et al. (2011) found the same nuclear LSU sequences of basidiomycetous Sebacinales in taxonomically unrelated plants growing in different areas, sometimes the association was mycorrhizal, sometimes endophytic, and they suggested that Sebacinales might play an important role in ecosystem integration. There are further complications when one looks at the endosymbionts of these fungi. Mycorrhiza-plant associations often include bacteria as additional partners, whether growing on the surface of the mycelium and synthesising crucial metabolites or living within the hyphae; bacteria are involved both in the establishment and the functioning of ectomycorrhizae (Frey-Klett et al. 2007). The bacterium Candidatus Glomeribacter gigasporarum (near Burkholderia) is found in the endomycorrhizal fungus Glomus (Castillo & Pawlowska 2009, 2010; Bonfante & Genre 2010). Such bacteria may affect the growth of the fungi, and they may be vertically transmitted like the fungi themselves (Bianciotto et al. 2003; Hoffman & Arnold 2009). Numerous bacteria (mostly Proteobacteria) are involved, and a diversity of fungi have been shown to be infected, although the relationship sometimes seems to be rather casual (Hoffman & Arnold 2010). However, bacteria can be integral to ECM associations, whether facilitating the establishment of the association (mycorrhiza helpers) or as integral to its subsequent functioning (Frey-Klett et al. 2007 and references); they have also been implicated in fixing nitrogen (Paul et al. 2007). Even viruses in endophytes may affect the ability of the host plant to grow in particular conditions (Márquez et al. 2007). Indeed, in several cases characteristic "plant" metabolites such as indolizidine (swainsonine) and ergoline alkaloids that are animal toxins are synthesized by the fungal or bacterial associates of the plant (e.g. Popay & Rowan 1994; Findlay et al. 2003 and Sumarah et al. 2010: spruce endophytes produce several metabolites toxic to the eastern spruce budworm; Gunatilaka 2006; Markert et al. 2008: Convolvulaceae; Pryor et al. 2009: Fabaceae; Wink 2008); Celastraceae and especially Poaceae are also distinctive in this regard. Such substances behave as if they were endogenous plant metabolites (Zhang et al. 2009; Friesen et al. 2011). Of course, secondary metabolites like terpenoids and quinolizidine alkaloids are produced more or less exclusively in mitochondria and/or chloroplasts - i.e. in a bacterial endophyte whose association is of very long standing (Wink 2008). 4. Evolution in stem group angiosperms. (This section needs lots of work.) The angiosperm stem group diverged from other seed plants (origin 1 above) by the late Paleozoic (Moldowan et al. 1994; E. L. Taylor et al. 2006). Candidates for fossil relatives of stem-group angiosperms include Corystospermales (Pteruchus, Ktalenia, etc.: Frohlich & Parker 2000), Bennettitales, and Caytoniales (poorly known in the younger Mesozoic). Cycadeoids or Bennettitales - "fossil beehives" - have long been associated with angiosperms (see also Doyle 2006 and Hilton & Bateman 2006 for cladistic analyses and literature). Other pteridosperm groups that have been linked with angiosperms are Pentoxylon and glossopterids, at least some of which had multiflagellate male gametes (Nishida et al. 2004: Soltis et al. 2008 for some references). Seed morphology and anatomy in particular, but also pollen morphology, suggest that Bennettitales should be placed in the BEG (Bennettitales, Erdmanithecales, Gnetales) group, and Erdmanithecales at least persisted into the Late Cretaceous (Friis et al. 2007, 2009a: four new genera in this complex, 2013; Mendes et al. 2010). However, Rothwell et al. (2009) and Rothwell and Stockey (2013) strongly questioned the idea of a close relationship between Bennettitales and Gnetales, notion i.a. that the former had spiral, not decussate, insertion of parts, the nucellus formed a plug in the micropyle, and there was no pollen chamber. The BEG group has radiospermic ovules that lack a cupule, they have a vascularized nucellus but not a vascularized integument, and their seeds have an outer sarcotesta, a sclerotesta, and a layer inside that (Rothwell & Stockey 2002). However, the reproductive morphologies of some of the early (Upper Triassic) Bennettitales are rather different from those of later fossils (e.g. Pott et al. 2010), and the interpretation of the complex reproductive structures of the group is not easy (see Crane & Herendeen 2009 for careful interpretations). Gnetaceae & co. themselves are far from having a flower, and the consensus of molecular studies is that Gnetaceae & co. are best placed sister to or inside Pinales (see extant seed plants); if so, the BEG clade has little to do with angiosperm origins. Indeed, the idea of any particular similarity between the "flower" of Bennettitales and those of angiosperms (Rothwell et al. 2008a, 2009; Crepet & Stevenson 2009, esp. 2010: c.f. relationships among angiosperms, tree topology sensitive to change of one character state in one taxon) has been questioned. Interestingly, the triterpenoid oleanane, found pretty much throughout angiosperms, also occurs in Bennettitales (Moldowan et al. 1994; E. L. Taylor et al. 2006). In any event, the envelopment of the seed to produce a fruit-like structure must have happened independently in the two (Rothwell & Stockey 2010). In some morphological analyses where Bennettitales do not group with the anthophytes and are associated with cycadofilicalean plants (Crepet & Stevenson 2009, esp. 2010), extant gymnosperms are also not monophyletic and Gnetales are sister to angiosperms. The challenge is to think of how the heterosporangiate strobilus with short internodes that is the angiosperm flower might have evolved from the separate male and female strobili of most gymnosperms. Rudall and Bateman (2010) suggested that the morphology of crown group conifers, being highly derived, might be of little help in thinking about that of the ancestors of angiosperms. This may seem to turn the problem over to the interpretation of fossil remains, and here there has been little progress over the last fourty years or so. In a comprehensive review on the bearing of fossil data on the origin of the flower, Doyle (2008b, see also Taylor & Taylor 2009) concluded that our understanding of the fossil record was insufficient to help much in understanding angiosperm origins. Similarities between the ovules of some Magnoliaceae and the cupules of Caytonia (e.g. Umeda et al. 1994) are probably superficial; features like the lobing of the integuments which induced this comparison seem to have little significance, certainly there is no suggestion that the two integuments of angiosperm ovules are of fundamentally different natures (Endress & Igersheim 2000; Endress 2005c). The ovule-bearing structures of Caytonia can be linked with the carpels of extant angiosperms by invoking appropriate morphological gymnastics (Doyle 2006 for literature, also Doyle 2008b; Doyle & Donoghue 1986a, b, 1992; Doyle & Endress 2010; etc.), but it does not make for satisfactory reading. X. Wang et al. (2007; X. Wang 2010b) has suggested that the early to mid Jurassic Schmeissneria, previously placed in Ginkgoales, is angiospermous, having closed carpels. Another mid-Jurassic fossil, Xingxueanthus, also has closed capels as well as a style (X. Wang & Wang 2010). X. Wang and Wang (2010) toyed with the idea that angiospermy may have arisen more than once and consider these plants to be stem-group angiosperms, and X. Wang (2010a) provided detailed descriptions of other possible pre-Cretaceous angiosperms. If columellate pollen is ancestral in angiosperms (but see above), there may be connections with the Triassic reticular-columellar Crinopolles-type pollen (Doyle 2001; Zavada 2007). Another approach is to think about morphology in the context of what is known about development, and this affects how one interprets fossils. Baum and Hileman (2006) proposed a developmental genetic model for the evolution of the flower which may help in the interpretation in the significance of particular fossils, and this and other models are summarized by Bateman et al. (2011b). Frohlich and Parker (2000) suggested that the heterosporangiate strobilus evolved in pteridosperms like Corystospermales from a male strobilus on which ectopic ovules developed - their "mostly male" theory of the origin of angiosperm flowers. LEAFY/FLORICAULA genes were likely to be associated with male reproductive structures, they suggested, and NEEDLY genes with female. However, work on the expression of LFY/FLO and NLY orthologs suggest that both genes are expressed in early-stage primordia, but the former are then expressed in ovules and microsporangia while the latter are expressed in the ovuliferous scale, aril, microsporophylls, etc. The expression of both genes in both male and female cones is not consistent with the "mostly male" theory (Vásquez-Lobo et al. 2007 and references; Moyroud et al. 2010; Tavares et al. 2010; see also Bateman et al. 2011b). Mathews and Kramer (2012; c.f. Kelley & Gassner 2009 for a more conventional approach) analyse ovule development in seed plants and floral development in angiosperms to think how these structures might have evolved; i.a. they suggest that evolution is less the change in form of pre-existing structures than the assemblage of new developmental modules in the context of homeosis, heterotopy, and heterochrony. Chanderbali et al. (2010) found that genes involved in microsporangium, etc., production in at least some gymnosperms are also expressed in the perianth of angiosperms; only a few genes involved in ovular expression are also expressed there. S. Kim et al. (2004b) age the split that gave rise to the paleo AP3 and PI genes to around (297-)290-230(-213) m.y., well before the origin of crown angiosperms, while Jiao et al. (2011) suggested that there was a whole genome duplication in these stem group plants - estimates of peak ages are (245-)236, 234(-225) m.y.a., the first half of the Triassic, although the spread of ages is 275-150 m.y. and Schranz et al. 92012) note that any connection between duplications and diversification was unlikely to be immediate. There have indeed been dramatic changes in the expressions of some genes during land plant evolution (e.g. Banks et al. 2011), but sampling is currently too poor to know where on the tree those changes coccured. Thus Szövényi et al. (2010: ca 30% of the genome mapped) noted that a total of only ca 5% of the genes in Funaria hygrometrica were expressed uniquely in the sporophytic and gametophytic generations, but in Arabidopsis ca 5% of the genes were differentially expressed in the gametophyte alone and ca 25% in the sporophyte alone. Gene expression in neither bryophyte generation was like that in the Arabidopsis gametophytes, but where in the tree between Funaria and Arabidopsis this shift might have taken place is unknown. For other such studies, see Lang et al. (2010) and Zhu et al. (2012). To summarise: ideas of relationships between angiosperms and other seed plants remain in limbo (Feild & Arens 2005, 2007; Taylor et al. 2009). In particular, it is unclear which seed ferns and relatives are to be linked with the stem-group of angiosperms, regardless of whether extant gymnosperms are monophyletic or paraphyletic or where Gnetales go on the tree (e.g. Rudall & Bateman 2010). 5. Relationships between extant angiosperms. Donoghue and Mathews (1998) had listed 16 different hypotheses of relationships among basal angiosperms that involved the first three nodes, but it now seems that Amborellaceae alone are sister to other angiosperms (not an hypothesis that Donoghue and Mathews included!), Nymphaeales
sister to the rest, then Austrobaileyales - the ANITA grade (e.g. Mathews &
Donoghue 1999; Qiu et al. 1999, 2000, 2001 [checked for long-branch attraction - none], 2005, 2006a, 2006b [some analyses], 2007; P. Soltis et al. 1999, 2000; Parkinson et al. 1999; Zanis et al. 2002; Magallón & Sanderson 2002; Kim et al. 2003; Borsch et al. 2003, 2005; Hilu et al. 2003; Nickerson & Drouin 2004; Aoki et al. 2004; P. Soltis & D. Soltis 2004; Müller et al. 2006a; Hansen et al. 2007; Duarte et al. 2008; McCoy et al. 2008). There have been suggestions of a basal [Amborellales + Nymphaeales] clade, perhaps particularly in analyses of mitochondrial genes (Qiu et al. 2006b), however, "it is sufficiently clear that the first diverging lineage of extant angiosperms consists of Amborella + Nymphaeales" (p. 845) seems something of an overstatement, and there are several unexpected if poorly supported relationships elsewhere in their preferred tree (Qiu et al. 2010) - see also Qiu et al. (2000, 2005, 2006a), Mathews & Donoghue (2000),
Graham et al. (2000), Stefanovic et al. (2004), Leebens-Mack et al. (2005), Cai et al. (2006), some trees in Jansen et al. (2006b), Bausher et al. (2006), Chang et al. (2006), Wu et al. (2007), Huang et al. (2010: c.f. rooting), Finet et al. (2010: support weak) and Moore et al. (2011: position not as stable as one might like...). Soltis et al. (2007; data from D. Soltis et al. 2000) found that the relationships obtained depended on the method of analysis; Bayesian analysis favoured [Amborellaceae + Nymphaeaceae], while parsimony yielded Amborellaceae as sister to the rest, while Goremykin et al. (2012) suggested that a wrongly specificied substitution model would produce the latter result. What kinds of characters are analysed may also be important; Goremykin et al. (2009b) found an [Amborella + Nymphaea] clade after removing a relatively few (500) highly variable positions from the analysis. For other studies, see Ruhlman et al. (2007), Jansen et al. (2007) and Moore et al. (2007). On balance, however, Amborella alone as sister to all other extant angiosperms is the most likely position; depending on how characters are optimised on the tree, the different topologies may have little effect when thinking about angiosperm evolution. There are of course still other topologies in the literature. Goremykin et al. (2003a) used complete chloroplast sequences, but for only 10 angiosperms, and suggested the relationships [[Amborellaceae + Calycanthaceae] [eudicots + monocots]], but poor taxonomic sampling with resultant long-branch attraction may be responsible for these results (D. Soltis & P. Soltis 2004; Jansen et al. 2004; Stefanovic et al. 2004; Degtjareva et al. 2004b; D. Soltis et al. 2004); monocots were represented by the highly derived Poaceae. Goremykin et al. (2004) found the same general result when adding Nymphaea; it linked with Amborella - which was still not sister to all other angiosperms. However, this study, too, suffers from the same basic sampling problem; grasses are highly derived monocots (see Kuhl et al. 2004 for the very distinct genome of Poaceae). Indeed, even when looking at complete chloroplast sequences of just a few flowering plants, the inclusion of Acorus, breaking up the long branch leading to Poaceae, had a major effect (Stefanovic et al. 2004), although there are also questions about the models used in the analyses (Lockhart & Penny 2005; Goremykin et al. 2005: monocots included did not always form a monophyletic group). Indeed, the non-monophyly of the monocots is a rather unlikely result that has been obtained in some studies where the nuclear gene 18S has been included (Troitsky et al. 1991: see Duvall et al. 2006 for references). Morton (2011: nuclear Xdh gene) found weak support for Ceratophyllaceae as sister to all other angiosperms, although otherwise much of the structure in her tree was similar to that of other studies mentioned here. A further complication was introduced by Lee et al. (2011), who found that Amborella and Nymphaeales were successively sister to other angiosperms, but then monocots were firmly placed as sister to the remainder, with a [magnoliid + eudicot] clade. This may be another sampling problem (Austrobaileyales, Chloranthales and Ceratophyllales were not included), but Lee et al. (2011) included massive amounts of data, almost 23,000 sets of orthologues from nuclear genomes. Different seed plant topologies were obtained from analyses using single genes or the same number of sites chosen from twelve separate loci (Burleigh & Mathews 2007a), and maximum likelihood and maximum parsimony analyses might show systematic error (Burleigh & Mathews 2007b). Sampling strategies may well be critical, particularly in analyses using relatively few taxa each with very large amounts of data. In some cases large amounts of data may indeed be the solution, in others, perhaps quite surprisingly little data per taxon but improved sampling will do the trick (e.g. Rokas et al. 2005; Hedtke et al. 2006), of course, exactly where sampling should be improved is important (Geuten et al. 2007), and each situation will have to be evaluated independently - little is new! The discovery that Hydatellaceae are sister to other Nymphaeales (Saarela et al. 2006) unexpectly allowed sampling in this area of the tree to be improved; however, the topology of the tree was unaffected. Finally, some kinds of DNA data may be positively misleading when it comes to understanding relationships (Duvall & Ervin 2004; Qiu et al. 2005; Duvall et al. 2006, 2008b; G. Petersen et al. 2006b). Horizontal transfer is notably common in mitochondrial genomes (Sanchez-Puerta et al. 2008, 2011; Hao et al. 2010; W[enqin] Wang et al. 2012; c.f. Cusimano et al. 2008). Fiz-Palacios et al. (2011) have suggested a number (25+) of "non-conventional" relationships in their study on land plant diversification, but this, too may be a sampling issue; I rarely mention these in the text. Interestingly, Barrett et al. (2012), using whole chloroplast genomes, found that adding data did not necessarily result in asymptotically stabilizing support values, rather, these continued to fluctuate even when relatively small amounts of data were added. Within angiosperms, there are convenient summaries of the copious literature on relationships between the major clades in e.g. P. Soltis & D. Soltis (2004), D. Soltis et al. (2005b) and Qiu et al. (2005). Much literature is cited at individual nodes here, see especially the notes immediately preceding the Magnoliales, and the monocots (also the [monocot + eudicot] clade), eudicots, pentapetalae/core eudicots, and asterids. The discussion below is based on the usually rather conservative topologies of the trees in this site. 6. Cretaceous History of Angiosperms. 6A. Introduction. The most comprehensive reviews of Cretaceous angiosperm history are those of Friis et al. (2006a, 2010a, 2011 in particular), on which this section draws heavily; see also Krassilov (1997), Dilcher (2010), Taylor (2010: focus on genes possibly involved; etc.). Doyle (2008b), Specht and Bartlett (2009), Endress (2010a), Doyle and Endress (2010), and others provide surveys of the floral morphology and biology of extant "basal" angiosperms. Hu et al. (2012) list early records of pollen and suggest possible pollinators, tabulate pollen morphology and possible pollinators of ANITA-grade angiosperms, magnoliids, "basal" eudicots and monocots, and finally optimise a number of pollen and floral characters on the tree. Age estimates of crown angiosperms vary considerably, mostly being in the range (210-)148-140(-130) m.y. (e.g. Doyle 2001; Sanderson & Doyle 2001; Wikström et al. 2001; Aoki et al. 2004; Davis et al. 2004a; Sanderson et al. 2004; Bell et al. 2005; Leebens-Mack et al. 2005; Moore et al. 2007; Soltis et al. 2008: a variety of estimates; Moore et al. 2010: 95% HPD); Bell et al. (2010) suggest ages of (199-)183(-167) or (154-)147(-141) m.y. depending on the method used. Estimates based on molecular data tend to be substantially older than others, Magallón (2008 and references; Magallón & Castillo 2009) noting ages of 182-158 m.y. and 130 or 241.7 m.y. respectively, i.e. mostly Lower to Middle Jurassic or older, for the basal split within angiosperms. Indeed, Smith et al. (2010: see esp. Table S3) recently suggested that crown angiosperms are (257-)217(-182) (with eudicot calibration) to (270-)228(-193) m.y.o. (without), and there are ages of 275-215.6 m.y. in Magallón (2010), (240-)205(-175) m.y. in Clarke et al. (2011: fossil calibrations), (256-)198(-163) m.y. in N. Zhang et al. (2012), and (257.9-)208.7-193.7(-157.7) m.y. in Magallón et al. (2013: with temporal constraints) for this clade; see also Schneider et al. (2004). If such early ages for crown angiosperm origin, some 270 to 175 m.y.a., so certainly Jurassic, if not earlier, are correct, we are faced with a series of problems. We have to rethink the ecological context of the evolution of angiosperms and of the insects associated with them, and then understand how angiosperms persisted as a presumably not very diverse clade for 50 m.y. or more. We are not immediately any closer to understanding which pteridosperms are close to angiosperms, but may need to include a different set of gymnosperm reproductive structures to link with the angiosperm flower. There are also differing narratives for later angiosperm evolution. Some suggest that angiosperms achieved ecological dominance by the end of the Cretaceous; others suggest that tropical rainforest as we know it had barely developed then, and that Cretaceous angiosperms were ecologically and physiologically rather unlike many of their Tertiary successors. As to events at the Cretaceous-Tertiary (K/T) boundary, some suggest that the bolide impact had a major effect only on North American plants, any more global effect being more muted; others suggest there were major changes in vegetation structure and composition at the K/T boundary and in the early Tertiary. Similar tensions are evident in the literature on the evolution of mammals, insects, etc. 6B. Early Angiosperm Evolution. Leaving these problems aside for the time being, unambiguous angiosperm fossils from before the Lower Cretaceous are at best few. Fossil pollen from the Cretaceous Valanginian-Hauterivian 141-132 m.y.a. is the oldest, although if columellate pollen is ancestral in angiosperms, there may be connections with the Triassic reticular-columellar Crinopolles pollen type (Doyle 2001; Zavada 2007). Diversification of angiosperms was well under way by 137 m.y. before present as judged by pollen remains, the only angiosperm fossils from that period, but it was 10-30 m.y. or more before crown group diversification really got going (e.g. Feild & Arens 2005). Thus in the Barremian-Aptian ca 125 m.y.a. (Early Cretaceous) there are some 140-150 taxa recorded from Portugal alone (e.g. Friis et al. 1999, 2000a, 2010b). All in all, a remarkably diverse flora, even if recent work suggests that a somewhat younger age for at least some of this material, perhaps Albian and ca 112 m.y., is more likely (Heimhofer et al. 2005, 2007). Although practically none of these fossils can be assigned to extant families, 85% of them represent plants of the magnoliid type or are somewhat monocot-like (Friis et al. 1997a, 1999, 2001; Heimhofer et al. 2007 - see also Doyle et al. 2008 for an evaluation of early fossils putatively of monocot origin; Friis et al. 2010a). Doyle (2001) noted the abundance of families with ascidiate carpels and exotestal seeds in these floras - and in extant members of the ANITA grade and Chloranthaceae. Doyle and Endress (2010) should be consulted for possible phylogenetic placements of a number of mostly magnoliid and ANITA-grade Cretaceous fossils, albeit the constraint tree used has a rather different topology that that of the main tree here. Moore et al. (2007) suggest some time between 148.6-135.5 m.y.a. for a rapid separation of the Chloranthales, magnoliid, monocot, eudicot and Ceratophyllales clades (see also Sun et al. 2011), although other dates are somewhat younger. There are fossils assignable to Chloranthaceae from the late Barremian ca 130 m.y.a. onwards, with some being very like the extant Hedyosmum (e.g. Crepet & Nixon 1996; Friis et al. 2006b for references). Pollen data suggest that monocots/magnoliids split in the early Aptian-mid Albian 125-105 m.y.a. (Heimhofer et al. 2005; Hochuli et al. 2006). Magnoliids diversified somewhat later for the most part (Friis et al. 1997a, 2006b for reviews); Lauraceae are prominent in the fossil record, and include the somewhat younger Early Cenomanian Mauldinia (Drinnan et al. 1990). This has distinctive condensed monosymmetric inflorescences quite unlike those of other Lauraceae, yet its flowers are very like those of extant members of the family. Jud and Wing (2012) thought that monocots and eudicots might have diverged 125-119 m.y.a., initial angiosperm diversification having occured within a mere 5-10 m.y. before that. There are several hypotheses about the ecological preferences of early angiosperms (see also vascular evolution). Most include the element that conditions were disturbed (e.g. Heimhofer et al. 2005; Berendse & Scheffer 2009 for a summary; Bond & Scott 2010; Boyce et al. 2010). Other than that, suggestions as to the conditions these plants faced vary. The first angiosperms may have been rather small (Friis et al. 2010b) tropical trees with sympodial growth that tolerated shady, humid and disturbed conditions, or other environments (e.g. Feild 2005; Feild & Arens 2005, 2007; Coiffard et al. 2006; Berendse & Scheffer 2009 for a summary); later there was movement into into more open conditions (e.g. Feild & Arens 2007; Bond & Scott 2010). Some suggest that angiosperms initially grew in semi-arid (e.g. Stebbins 1965, 1981; Hickey & Doyle 1977) or at least seasonally arid (Bond & Scott 2010) conditions, and some early leaf floras from Portugal do have leaves that are small in size and xeromorphic in appearance (Friis et al. 2010b). Early nymphaealean-type plants are likely to have grown in aquatic or marsh-like habitats (e.g. G. Sun et al. 2008), while Coiffard et al. (2012) emphasized that in that the first stage of the rise to dominance of angiosperms, 5/11 genera were aquatics, and they "competed with charophytes". They did not say that the ancestral angiosperm was aquatic, but Goremykin et al. (2012) do think that this is likely. However, both very xeromorphic plants and plants with a highly-derived aquatic habit are likely to be derived; at the very least, thought needs to be given to stelar evolution. In any event, whether Nymphaeales are sister to Amborellaceae or not will have little effect on ancestral reconstructions of habitat preferences. Furthermore, that the angiosperm progenitor was a "diminutive, rhizomatous to scrambling herb" seems unlikely (Taylor & Hickey 1992, p. 137: an extension of the palaeoherb hypothesis), although at least some early angiosperms may have been herbs (e.g. Friis et al. 1999 and references). Whatever habitats angiosperms first favoured, there is a consensus that they were soon components of disturbed, mesic communities (Hickey & Doyle 1977). The conditions in places where they grew are described as being well lit or open (e.g. Royer et al. 2010); mention of flood-plain like habitats for early angiosperms is common (e.g. Wing & Boucher 1998; Coiffard et al. 2008). Aethophyllum, a small (but hardly herbaceous), fast-growing conifer (?Voltziales), had occupied similar habitats in the lower middle Triassic (Rothwell et al. 2000). How woody the early angiosperms were is unclear; Philippe et al. (2008) suggested that they might have had cambium, but there were no thick-walled fibres and in general cell walls were thin (see also Amborella); they are likely to have been shrubby plants (Hickey & Doyle 1977). In any event, any climatic niche evolution that occurred may have been slow, i.e., habitat evolution was slow (Smith & Beaulieu 2009). Growth rates may have been high and reproduction rapid compared with those of gymnnosperms (Doyle & Hickey 1976; Bond 1989; Wing & Boucher 1998; Verdú 2002). The reproductive cycle was relatively short, with a short time between pollination and fertilization, seeds were small (see below), the plants were small, overall, there was a short pre-reproductive period and generation time (e.g. Williams 2008, 2009; Crepet & Niklas 2009 Bond & Scott 2010). The flowers of early angiosperms are likely to have been small and rather generalised (see e.g. Crane et al. 1995; Doyle & Donoghue 1986a; Friis & Crepet 1987; Friis & Endress 1990; Friis et al. 2000, 2006b, 2010b; Endress 2001a; Weberling 2007; Doyle 2008b; Doyle & Endress 2000, 2010, 2011). The stamens of fossils are often wedge-shaped, with a massive apex, stout filaments and connectives, and anthers open by laterally-hinged valves (e.g. Crepet & Nixon 1996; Endress 2008c and references; Endress 2011a) - although perhaps not in the earliest angiosperm fossils. Dry stigmas and protogyny were probably the common condition (e.g. Sage et al. 2009; Endress 2010a). These small flowers were probably aggregated into inflorescences to attract pollinators (Friis et al. 2006b). The carpels are likely to have had few ovules, Doyle (2012) suggesting that the ancestral state is to have a single ovule, and the stamens only a few pollen grains (e.g. Crepet et al. 1991; Dilcher 2000; Friis et al. 2006b). However, quite "derived" features are early evident. Thus in Sinocarpus, from the Barremian-Aptian 139-122 m.y.a., the carpels were apparently connate at the base (Leng & Friis 2003), and inferior ovaries were surprisingly common (e.g. Crane et al. 1995; Friis et al. 1999). If extant magnoliid and ANITA-grade angiosperms are any guide, distinctions between different kinds of floral parts might be hard to make. There distinguishing perianth and prophylls and bracts can be difficult, there can be intermediates between perianth and stamens, the numbers of parts and their arrangement vary, etc. (Buzgo et al. 2004; Taylor et al. 2008; Endress 2008a; Doyle & Endress 2011 and references). The seeds of early angiosperms were dry (but see Eriksson et al. 2000a, esp. b) and mostly rather small compared with those of extant gymnosperms (Tiffney 1986a; also Haig & Westoby 1991; Linkies et al. 2010); the seed contents, probably mostly endosperm reserve, were a mere 2-3 mm3. A small size is perhaps to be expected since plant and seed size are quite strongly linked (e.g. Eriksson et al. 2000; Moles et al. 2005b). The embryos themselves are likely to have been small to minute (measured as the embryo:seed ratio), resulting in a period of morphological dormancy before a plantlet developed and germination could occur (Forbis et al. 2002; Linkies et al. 2010). Indeed, seeds of plants in the ANITA grade are mostly notably smaller than those of extant gymnosperms (e.g. Moles et al. 2005a), and the embryo is small. It was early recognized that angiosperm leaves are very different from those of most gymnosperms and other vascular plants (Hickey & Doyle 1977). Some early fossils had leaves with a multistranded midrib, they were simple, with entire margins and irregular venation. The regularity of the venation increased, blades having several orders of venation, as well as teeth, and compound leaves became more common. Vegetative evolution was a major element in early angiosperm diversification (Hickey & Doyle 1977), and the increase in venation density represented by these leaves with more ordered venation can be linked to increased photosynthesis and all that that implies (e.g. Boyce et al. 2009; Feild et al. 2011b; Boyce & Leslie 2012 see
below). Many older plant fossils have very distinctive character combinations (e.g. Feild & Arens 2005; Fries et al. 2011 and references). For example, Archaefructus, probably an aquatic herb that lived in the Barremian-Aptian at least 124 m.y.a. (Sun et al. 2002), has been interpreted as having perfect flowers that are unlike those of any extant angiosperms - there is no perianth, the receptacle is very elongated, the stamens are paired, and the carpels are conduplicate - or these "flowers" are inflorescences, the paired stamens representing staminate flowers that lack any other structures (see also Zhou et al. 2003; Friis et al. 2003b; Ji et al. 2004; Doyle & Endress 2007; also Crepet et al. 2004 for critical analyses of this and other early fossil angiosperms). Whatever the interpretation, Archaefructus is unlikely to be sister to all extant angiosperms (c.f. Sun et al. 2001; Crepet et al. 2004), recent morphological work suggesting that it could be a member of Nymphaeales (Doyle & Endress 2007, 2010a; Doyle 2008b). Some fossils, perhaps including Archaefructus itself, may represent quite distinct but now extinct clades (von Balthazar et al. 2008). Hyrcantha, also more or less aquatic, is also from Barremian-Aptian deposits in China (Dilcher et al. 2007); it has leaves with sheathing stipules and partly connate carpels with apparent resin bodies at their apices. Fossils from the Aptian/Albian ca 112 m.y.a. continue to have odd assemblages of characters (see also Friis et al. 1995). Quite a variety of strange-looking putative angiosperms have been discovered in northeastern China, and although the identities of a number are disputed (Sun et al. 2006), new fossil finds from this area continue to challenge our understanding of angiosperm evolution (Sun et al. 2011: see eudicots below). Perhaps more remarkably, fossils ascribed to Sarraceniaceae (asterids, Ericales) have been described from deposits about the same age as those in which Archaefructus was found (Li 2005); this does seem something of a stretch. As to what pollinated these early angiosperms, Labandeira (2010 and references) suggested that many pollinating clades of Hymenoptera, Diptera, and Lepidoptera originated around Late Barremian/end Albian some 125-100 m.y.a. Early angiosperms are likely to have been pollinated by insects (Hu et al. 2008), although Hu et al. (2012 and references) suggest that pollination by both insects and wind (ambophily) may also have occurred. Thermogenic (beetle) pollination is found in some extant members of many "basal" lineages, including Araceae, although not Laurales, Amborellales, and Acorales (Thien et al. 2000; Seymour et al. 2003; Seymour 2010). Beetles are quite common pollinators of ANITA and magnoliid angiosperms, including Calycanthaceae, and are attracted to haplomorphic flowers lacking definite symmetry signals (Leppik 1957); of course, other factors such as scent and thermogenesis are also involved. Pollen seems initially to have been produced in rather low quantities, yet at first the stamens in particular seem to have been a source of food, and pollen has been found in coprolites (Friis et al. 1999). The few dispersed pollen morphs and the diversity of pollen morphs associated with plant remains suggests some kind of insect pollination (Friis et al. 1999), however, there is no signal of an increase in protein content of the pollen of extant representatives of basal angiosperm clades that suggests bee pollination (Roulston et al. 2000), and bees are unlikely to have been pollinators of early flowers; certainly, their diversity was low then (e.g. Grimaldi & Engel 2005). Furthermore, pollen is not often clumped (Doyle et al. 1975; Hu et al. 2008) and nectar is unlikely to have been a common reward at this time, although "food bodies" have been reported in 115-100 million year old flowers from Lower Cretaceous Burmese amber (Santiago-Blay et al. 2005). Bee larvae obtain their fat from pollenkitt (Renner 2010) which is produced by the degeneration of the tapetum and is rich in plastid-derived lipids. Interestingly, evidence suggests that early bees were oligolectic, not polylectic (Litman et al. 2011 and references: note early ages for bee diversification; also Sedivy et al. 2012; c.f. e.g. Moldenke 1979), so they would visit relatively few species of flowers, although these might be related (as with today's oligolectic bees). Dispersal of dissseminules is initially likely to have been by wind (Wing & Boucher 1998). Eriksson et al. (2000b) sampled some 100 taxa from the Barremian-Aptian (132-112 m.y.a.), and even then ca 25% were animal dispersed, although in size they were still very like the abiotically-dispersed propagules that predominated in early angiosperms (see Tiffney 1984; Eriksson 2008; Dilcher 2010, in part; Sussman et al. 2013). In the Portugese Late Barremian-Aptian 124-112 m.y.a. climate and environment were unstable, which might have favoured angiosperms if they were adapted to disturbed habitats (Heimhofer et al. 2005); angiosperms diversified towards the end of this period, and the following Albian was a warmer and drier time (see also Coiffard et al. 2006, 2007). Tricolpate pollen, the signal of eudicots, has been reported from the Late Barremian-Early Aptian some 125-120 m.y. (e.g. Magallón et al. 1999; Sanderson & Doyle 2001). However, if the identity of Leefructus from early Cretaceous deposits 125.8-122.6 m.y. old in China and assigned to stem Ranunculaceae (Sun et al. 2011: no pollen) is confirmed, these ages will have to be revised. In west Portugal and elsewhere tricolpates are initially in low numbers, but in the Early Albian ca 112 m.y.a. angiosperms, including tricolpates, diversified rapidly (Heimhofer et al. 2005; Friis et al. 2006b for references). It has been suggested that the functional advantage of tricolpate pollen is that the grains may germinate faster, even if they remain viable for a shorter time than monoaperturate pollen (e.g. Furness & Rudall 2004). Somewhat younger (120-110 m.y.) monocot pollen has been identified as Araceae-Pothoideae (Friis et al. 2004; see also Doyle et al. 2008: Friis et al. 2010), although some early monocot records have been questioned (Hoffmann & Zetter 2010). Overall monocot fossils are not very common, but being a predominantly herbaceous group they may have fossilized less well. Fossil angiosperm wood is known from deposits of up to about 120 m.y. age (Aptian), although its assignment to extant clades is not easy (Oakley et al. 2009). 6C. Later Cretaceous Evolution. The Late Cretaceous begins ca 99.6 m.y.a. with the Cenomanian, the sea during this period being about one hundred and fifty meters above its present level. I also include somewhat earlier dates in this section, the period from 110-80 m.y.a. encompassing the so-called Cretaceous Terrestrial Revolution (CTR: Meredith et al. 2011). A long-term warming trend from the early Aptian culminated in the Cenomanian-Turonian thermal maximum ca 99 m.y.a. (Heimhofer et al. 2005). Atmospheric CO2 concentrations had reached their highest concentration, perhaps as much as around 1,600 ppm around the Jurassic-Cretaceous boundary, possibly the highest concenrations since their dramatic deline in the late Devonian ca 360 m.y.a., and were declining; global temperatures show a similar overall trend (Shi & Waterhouse 2010; Franks et al. 2013). This period has been characterised as one in which major changes in the terrestrial vegetation occurred (e.g. Crepet 2008; Coiffard & Gomez 2011, 2012). Some low altitude floras were dominated by angiosperms even in the Cenomanian-Turonian (Coiffard & Gomez 2012 for references), and in mid latitude floras were changing considerably, fossil woods becoming notably more common (Philippe et al. 2008; Wheeler & Lehman 2009), although angiosperms seem to have been relatively minor components of the vegetation until the end of the Cretaceous (Coiffard & Gomez 2012). About this time there was also diversification of mammals, the net diversification rate showing a major increase around 80 m.y.a. at the end of the CTR, immediately followed by a comparable decrease (Meredith et al. 2011). Indeed, Meredith et al. (2011: p. 523) observed that the evolution of angiosperms was "a key event in the diversification of mammals and birds" (but see below). The evolution of bees, major pollinators of angioosperms, and other insects, both pollinators, seed dispersers (esp. ants) and herbivores, is particularly important. Cardinal and Danforth (2013) estimated that bee diversification began (132-)123(-113) m.y., with families having diverged by the beginning of the Tertiary; most diversification occured within the last 100 m.y. (see also Grimaldi 1999: beginning ca 112 m.y.a.; Engel 2000; Grimaldi & Engel 2005). Initial divergence within butterflies s.l. (Papilionoidea) may also have been around 110-95 m.y.a. (Heikkilä et al. 2011). Grimaldi and Engel (2005) suggest that stem ants date to ca 120 m.y.a. Wang et al. (2008) support this general idea, noting that there was contemporaneous diversification of ants, mosses, beetles and hemipterans. Locally, herbivory was quite prominent (Labandeira et al. 2002b). The sugar-rich fruits of angiosperms may have provided a habitat for budding yeasts such as Saccharomyces cerevisiae; they have a genome duplication ca 100 m.y.a. that is perhaps connected with their ability to exploit this habitat (Wolfe & Shields 1997; Conant & Wolfe 2007). For the evolution of yeasts able to grow in nectar, etc., largely a Tertiaty phenomenon, see Guzmán et al. (2013). Over a period of about 49 m.y. angiosperms spread latitudinally from the more tropical environments they initially inhabited (Axelrod 1959; Hickey & Doyle 1977; Wing & Boucher 1998; Hemihofer et al. 2005 for further references), moving polewards in the early Late Cretaceous (Pott et al. 2012 and references); abundance incresaed in a similar fashion. There were a significant number of eudicots in mid-latitude North America in the Albian-Turonian, ca 100 m.y.a., although again slightly earlier at lower latitudes, that is, palaeolatitudes S of 30 N (e.g. Crane & Lidgard 1989, 2000; Lupia et al. 1999), and they replaced free-sporing plants (see also Fiz-Palacios et al. 2011: "continuous replacement"), but not conifers (see e.g. Wing & Boucher 1998; Lupia et al. 1999); cycads may also have declined. Areas where conifers remained common seem to have become more restricted, and ecological factors such as slow seedling growth, details of leaf construction, low stomatal width (ca 2 µm: Walker 2005), etc. - despite a very high leaf area index of up to 21 (Maguire et al. 2005) - can be adduced to explain this change (e.g. Bond 1989). At the same time, many of these features of conifers make them formidable competitors with angiosperms in well-lit conditions in other than nutrient-rich soils (Brodribb et al. 2012). The decline of cycads and Bennettitales (cycadophytes, an ecological grouping) might be linked with the contemporaneous decline in herbivorous stegosaurian dinosaurs, but there is no indication of any even loose relationships between early angiosperms and dinosaurs (Butler et al. 2009 and references). In Australia, angiosperm pollen had increased from a low level in the middle Albian ca 105 m.y.a. to about 35% of the total spores at the end of the Cretaceous, while that of free sporing plants dropped from 80% to 45% of the total during the same period; however, not all fern families behaved the same, and there were differences between Australia and North America (Nagalingum et al. 2002). By the mid-Cretaceous pollen became more abundant and is quite often found in clumps, suggesting that the pollinators, perhaps bees, were becoming more specialized (Hu et al. 2008; Leslie & Boyce 2012). However, there is no obvious signal of an increase in protein content of the pollen of extant representatives of angiosperm clades that had probably evolved by then that would suggest a shift to bee pollination (Roulston et al. 2000); diversification of bees is estimated to have begun ca 125 m.y.a. (Ronquist et al. 2012) or perhaps as late as 100 m.y.a. (Grimaldi & Engel 2005). Diversification of eudicots in the Cenomanian-Turonian 110-90 m.y.a. has been linked with the evolution of bees; certainly, angiosperm flowers from this period showed a variety of quite specialized zoophilous morphologies, and nectar secretion became common (Crepet 1996, 2008; Hu et al. 2008), and by the end of the Cretaceous clades representing today's families and tribes of bees had diverged (Grimaldi & Engel 2005). Citerne et al. (2010) suggested that 93.5-89 m.y.a. in the Turonian was a period of floral innovation and evolution of polllinators. There are nectaries in fossils of Cenomanian age, while sympetaly and monosymmetry (evidence for the latter is indirect, seeds assignable to Zingiberales: Rodríguez-de la Rosa & Cevallos-Ferriz 1994) appear in the Late Cretaceous (Friis 1985; van Bergen & Collinson 1999; Friis et al. 2003a). With the advent of the core eudicots in particular by ca 109 m.y.a. nectar produced by receptacular nectaries may have become a major reward for pollinators (Friis et al. 2006b). Note that some Proteales have receptacular nectaries, and some fossils of Platanaceae (also Proteales) are also described as having nectaries. Septal nectaries may be an apomorphy for monocots, being scattered throughout that clade, and are certainly found in some Alismatales, and their evolution is also early. (Nectaries of various other types are found in a few angiosperms other than monocots and core eudicots.) The major groups of asterids, and rosids - and of monocots - probably had all diverged by the earlier part of the Cretaceous (Sanderson et al. 2004). Pollen suggests core eudicots may have been around since the Albian 125-112 m.y.a., and clades like Dipsacales, major clades of both rosids and monocots, etc., may all have radiated rather rapidly in this general period (Jian et al. 2008 and references; Wang et al. 2009). Flowers assignable to a variety of asterid groups and also to Saxifragales (ovary inferior, crowned by a nectary, styles more or less separate, i.e. they look very like the old woody Saxifragaceae) being especially well represented, as are Ericales (Friis et al. 2006b). Indeed, Saxifragales, although now not very speciose, may also represent an ancient and rapid radiation (Fishbein et al. 2001; Fishbein & Soltis 2004), early divergence of the main clades perhaps occurring over a period as short as 3-6 m.y. (Jian et al. 2008). Crane and Herendeen (1996) note that fossils referable to extant angiosperm families appear in east North America around 115-90 m.y.a., and by some 85 m.y.a. their diversity had increased considerably (see also Lidgard & Crane 1988; Friis & Crepet 1987; Friis & Endress 1990; Crepet et al. 2004, etc.). Rosids in particular seem to have been common in the Late Cretaceous (Friis et al. 2010b), and diversification of the major rosid clades may have occurred (114-)108-91(-85) m.y.a., and those of Fabidae and Malvidae very soon after, (113-)107-83(-76) m.y.a. (Wang et al. 2009). The origins of several clades within Malpighiales and Ericales whose representatives now are major components of lowland tropical rainforest (l.t.r.f.)are also to be pegged to the Mid Cretaceous or slightly later, dates in the former being some time in the late Aptian/Albian, (119.4-)113.8(-110.7)/(105.9-)101.6(-101.1) m.y. ago (Davis et al. 2005a: high and low estimates). Initial diversification was rapid, and relationships have been hard to disentangle there (Wurdack & Davis 2009; but c.f. Xi et al. 2012). Crown group Menispermaceae have been dated to around 109.1-106.3 m.y.a. (W. Wang et al. 2012), and this family is now most common in tropical rain forests where it is prominent in the liane element of the vegetation; t.r.f. is probably its ancestral habitat (W. Wang et al. 2012). However, Burnham (2009) noted that there were few fossils of climbers through most of of the Mesozoic, although a few angiosperm climbers are known from the Cretaceous; wood fossils of lianes from the Cretaceous-Palaeogene are dominated by Ranunculales and Vitaceae-Vitoideae (Smith et al. 2013: no Vitoideae yet known from the Cretaceous). Plants with distinctive pollen assignable to the Normapolles complex (Fagales) were both diverse and ecologically prominent in rocks from east North America to western Asia from the Late Cenomanian/Early Turonian ca 93.5 m.y.a.; of the other pollen provinces, the southernmost was also characterized by pollen from Fagales (e.g. Pacltová 1981 for a review; Kedves & Diniz 1983; Friis et al. 2006b, 2010b). Fagales are important ecologically, and today are largely ectomycorrhizal and temperate-tropical montane. A flower, the Rose Creek fossil, unequivocally identified as a core eudicot but not as any extant family, is known from the Cenomanian some 96-94 m.y.a. (Basinger & Dilcher 1984). It is relatively large compared to the tiny flowers of other Cretaceous angiosperms and the five stamens are somewhat unexpectedly opposite the petals; it is the earliest fossil flower with a nectary (Friis et al. 2011). Crepet (1996, 2008) noted the first appearance of many largely core eudicot characters beginning in the Albian, but especially Cenomanian/Turonian some 96-88 m.y.a.; indeed, the diversity of floral form in the Turonian of east North Americas is very considerable, magnoliids, rosids and asterid-Ericales all being represented (e.g. Crepet & Nixon 1996). However, even up to the Cenomanian ca 96 m.y.a. there are many fossils that probably belong to the ANITA-magnoliid grade (e.g. Coiffard et al. 2006; Kvacek & Friis 2010; Friis & Pedersen 2011). Around 108 m.y.a. the venation density of angiosperms had become markedly greater than that of non-flowering plants and ANITA-grade angiosperms (Feild et al. 2011b; c.f. Bond & Scott 2010 in part), and atmospheric CO2 concentration was in its long decline from the late Jurassic-early Cretaceous that finished only in the later Oligocene ca 40 m.y.a. (Shi & Waterhouse 2010; Franks et al. 2013). Friis et al. (2006a; see also Heimhofer et al. 2005) note a dramatic increase of phylogenetic diversity and ecological abundance of angiosperms at this time, and there was a small increase in the net diversification rate of mammals (Meredith et al. 2011). Indeed, examination of the teeth of multituberculate mammals suggests that a radiation began ca 85 m.y.a. in which the adoption of a more herbivorous diet may be associated with this increasing prominence of angiosperms (G. P. Wilson et al. 2012). Later in the Cretaceous angiosperm diversity was increasing, being high even close to the Arctic Circle (Hofmann et al. 2011), and angiosperms may have achieved at least some measure of ecological dominance (Friis et al. 2006b). Large trees first appear in the fossil record in the Late Albian to Cenomanian (ca 90.6 m.y.), and trends like increasing seed size were already evident, probably connected with the increasing size of woody plants (e.g. Eriksson et al. 2000a; Forbis et al. 2002; Linkies et al. 2010), thus a general increase in fruit size occured at about 85-75 m.y.a. (e.g. Eriksson et al. 2000a; Dunn et al. 2007). Interestingly, diversification of polypod ferns began in the Cretaceous (Schneider et al. 2004; Schuettpelz & Pryer 2009), perhaps associated with the evolution of a distinctive new photosystem that allowed them to grow in shady conditions (Kawai et al. 2003). The origin of epiphytism in ferns as a whole seems to have occurred in the mid-Cretacous or rear the K/T boundary, even if diversification was a Tertiary phenomenon (Dubuisson et al. 2009). Similarly, diversification in the speciose pleurocarpous mosses, about 40% of all mosses, seems to have been early-Cretaceous and rapid, with subsequent semi-stasis. Many mosses, especially members of Hypnales, are epiphytic (Shaw et al. 2003b; Newton et al. 2006, 2007; see also Kürschner & Parolly 1999), and the initial radiation is at about the same time as the early rise of the angiosperms. Porellales, largely leaf-epiphytic liverworts, diverged from the terrestrial Jungermanniales in the Jurassic, but there may have been enhanced diversification of Porellales in the Cretaceous and early Tertiary (Heinrichs et al. 2007; see also Ahonen et al. 2003; Forrest & Crandall-Stotler 2004). Lejeuneaceae initially diversified in the Cretaceous, and here there was no change in rate through the Tertiary (R. Wilson et al. 2007a, b) and there was no obvious change in Cephaloziineae (Feldberg et al. 2013). Diversification of mosses accelerated in the Cretaceous as rates had decelerated for liverworts and gymnnosperms (Fiz-Palacios et al. 2011; c.f. Cooper et al. 2012 for problems with the study). Cooper et al. (2012) suggested that although many liverwort families diverged in the Cretaceous and other splits in liverworts were very much older, much divergence within the families was a Tertiary phenomenon. Through much of the Cretaceous, any dominance of angiosperms may have tended to be restricted to fluvial or disturbed environments. Areas with ever-wet tropical humid climates seem to have been initially rather restricted in the Cretaceous (see also Boyce et al. 2009, 2010; Boyce & Lee 2010; Feild et al. 2009a). Even if there was tremendous phylogenetic diversification in the later Cretaceous and early Tertiary - which clearly is at issue - that transformative ecological change came later (e.g. Feild et al. 2011b) perhaps underestimates the effects of the Cretaceous Terrestrial Revolution. Interestingly, stem-group Rafflesiaceae are estimated to have diverged from other Malpighiales some 95 m.y.a., with Sapria, representing the first clade to split off from the rest, diverging some (95.9-)81.7(-69.5) m.y.a. (Bendiksby et al. 2010); this might suggest the presence of t.l.r.f., the habitat where Rafflesiaceae now largely grow. Mycoheterotrophic clades of Dioscoreales grow in similar habitats and are estimated to have diverged (118-)109-79(-68) m.y.a., with the mycoheterotrophic habit being established by some time before the beginning of the Palaeocene ca 65 m.y.a. (Merckx et al. 2010). Just how ecologically dominant angiosperms had become in the later Cretaceous remains unclear. Many angiosperms may have grown in aquatic habitats (Barremian), and later were to be found in shady or disturbed flood plain-type habitats (e.g. Feild & Arens 2005, 2007; Coiffard et al. 2006, 2007). In the Albian-Cenomanian of Europe angiosperms were most evident in backswamp, flood plain, levee, and braided river habitats (Coiffard et al. 2006). Coiffard and Gomez (2009: p. 164) suggest that the Late Cretaceous was the "dawn of modern angiosperm forests", but their Turonian forests grew primarily in disturbed and/or river associated habitats; Platanaceae, found along channel margins in the Cenomanian, had spread onto flood plains in the Turonian. Bond and Scott (2010) suggest that until the Mid or even Late Cretaceous angiosperms were mostly small herbs to small trees of the understory growing in dryish conditions, perhaps rather weedy plants (Feild et al. 2011b). Taken together, this suggests a variety of water relationships for these early plants. In their discussion of Cretaceous angiosperm ecology, Wing and Boucher (1998, p. 379) concluded that at the end of the Cretaceous, diversification of flowering plants represented "the evolution of a highly speciose clade of weeds but not necessarily a major change in global vegetation", while Eriksson et al. (2000) suggest that Late Cretaceous vegetation was open, rather dry (leaf size was relatively small - Upchurch & Wolf 1987), and disturbed by herbivores (see also Schönenberger 2005; Wing et al. 2012). Fires were relatively common throughout the Cretaceous, and they may have encouraged/been encouraged by a rather shrubby, low stature vegetation with a relatively short life cycle (Bond and Scott 2010; Bond & Midgley 2012). However, angiosperms may have formed a canopy at least locally by the end-Cretaceous (e.g. Upchurch & Wolfe 1987; Crane & Lidgard 1990; Boyce et al. 2010), but how diverse that forest was is unclear. In parts of North America, at least, angiosperms in the Campanian seem to have lived in rather species-poor and open woodland (Lehman & Wheeler 2001; Wheeler & Lehman 2001, 2009). Since the trees - perhaps to 50 m tall and 1.3 m across - may have produced Normapolles pollen (Lehman & Wheeler 2001), commonly associated with ectomycorrhizal Fagales, a diverse forest might not be expected, however, identifications of these woods rarely includes Fagales... (Wheeler & Lehman 2009). However, by the North American Campanian ca 80 m.y.a. angiosperms came to make up ca 40% of both floristic diversity and abundance even at higher latitudes (Lupia et al. 1999; see also Nagalingum et al. 2002), and there was an end-Cretaceous rise to dominance of angiosperms in Patagonia (Iglesias et al. 2011). It may be noted that there was a second major increase in angiosperm venation density at the end of the Cretaceous (Maastrichtan) ca 70 m.y.a. Only then did trees having a venation density similar to that of plants in the most productive t.l.r.f. today appear (Brodribb & Feild 2009; Feild et al. 2011b). To conclude. The "museum" hypothesis of Tertiary diversification suggests that many clades persisted largely unaffected across the K/T boundary (Stebbins ), or there was initial rapid diversification which slowed down as global cooling occurred ("ancient cradle"), or there was a progressive increase in diversification rate towards the present, the "recent cradle" theory (see Couvreur et al. 2011c for references). The museum hypothesis is consistent with the suggestion by Fiz-Palacios et al. (2011: c.f. ages) that the diversification rate of angiosperms was constant through the Cretaceous, while Couvreur et al. (2011c) found that the rate for palms held more or less constant for some 65 m.y. after their origin ca 100 m.y.a., right across the K/T boundary. Annonaceae (Couvreur et al. 2011a; see also Erkens et al. 2012), Araceae (Nauheimer et al. 2012) and the liverwort groups Lejeunaceae (R. Wilson et al. 2007) and Cephaloziineae (Felberg et al. 2012) show a similar pattern. Similarly, the diversification rate of the main clades of ants may have been constant (Pie & Tschá 2009), and rather surprisingly, given text-book accounts, mammal diversification seems to have been little affected by the end-Cretaceous extinction event (Bininda-Emonds et al. 2007; Meredith et al. 2011; G. P. Wilson et al. 2012; c.f. O'Leary et al. 2013). Palms are iconic plants of t.l.r.f. today, so either the rainforest of 100 m.y.a. was rather different from that of today (see e.g. Feild et al. 2011b), or t.l.r.f. of "modern" aspect remained very restricted in extent for millions of years, or there are methodological problems with the analyses (see e.g. Quental & Marshall 2010). However, Coiffard and Gomez (2009) suggest that early palms may have been swamp plants plants like living basal Arecales (their examples were Calamus, Nypa, and Mauritia). These scenarios are not all mutually exclusive, certainly, many major angiosperm clades diversified well after the palms, mostly in the Tertiary, and this would include families like Fabaceae as well as the more herbaceous members of the asterid I + II clades. 7A. Mostly Flowering Plants. The end-Cretaceous bolide impact that occurred ca 65.5 m.y.a. seems not to have been accompanied by widespread fires (Belcher 2010). Nevertheless, it caused up to 80% loss of plant species, at least in some places in North America (Upchurch & Wolf 1987), and there was concomitant extinction of diet-specific herbivorous insects as evidenced by a survey of the types of leaf damage caused by herbivores (Labandeira et al. 2002a, b; Wilf 2008). Indeed, in North America the vegetation seems to have suffered "sudden ecosystem collapse", at least locally, even common plants not transgressing the Cretaceous/Tertiary boundary (Wilf & Johnson 2004), although the severity of the impact seems to have depended in part on physical location (Johnson & Ellis 2002). Both insect-pollinated and/or evergreen taxa sof seed plants uffered more than wind-pollinated and/or deciduous taxa (Collinson 1990; McElwain & Punyasena 2007). In New Zealand the iridium anomaly associated with this impact was followed by a thin layer high in fungal remains (Vajda & McLoughlin 2004), while in both hemispheres there are fern spikes (and, in the Netherlands, a bryophyte peak) after the impact (Vajda & McLoughlin 2007 and references; Nichols & Johnson 2008). Evidence from Australia is unclear (e.g. Macphail et al. 1994; Hill & Brodribb 2006). However, in Patagonia in particular and perhaps the Southern Hemisphere in general, changes at the K/T boundary were rather muted (Wilf etb al. 2013). Groups other than plants and dinosaurs suffered; there are estimates of about 60% loss of butterfly diversity at the K/T boundary (Wahlberg et al. 2009), a mass extinction of birds in western North America, but perhaps elsewhere, too (Longrich et al. 2011), and a 83% extinction of snakes and lizards in North America (Longrich et al. 2012). However, as already noted, individual plant groups (palms) and animal groups (ants, mammals) seem little affected, and although marine extinctions were quite common, both the extent of K/T extinctions and even their cause(s) are still somewhat problematic (Schulte et al. 2010; c.f. Science 328: 973-976. 2010). Crown-group placental mammals may be entirely Tertiary in age (O'Leary et al. 2013). Estimates of the time that the vegetation took to recover from the impact range from anything from only a few thousand (Vajda & McLoughlin 2007) to over a million (McElwain & Punyasena 2007) years, depending on where on the globe the forests were. Similarly, recovery of algal primary productivity in marine ecosystems may have taken as little in the order of century or perhaps even less (Sepúlveda et al. 2009: Denmark), although most estimates of marine recovery are longer (literature in Wilf & Johnson 2004). In North America there may have been initial recolonization by swamp- and mire-loving plants, which survived the impact better (Johnson 2002; Labandeira et al. 2002b), and deciduous vegetation was also prominent early in the Palaeocene (Collinson 1990). Some floras in western interior United States from ca 2 m.y. after the impact (early Palaeocene) have low plant diversity (deciduous species with thin leaves and low defences) and so a high diversity of insect damage, while others are more diverse and have the facies of tropical fainforest (tough, thick, probably tanniniferous leaves) and with a low diversity of insect damage - i.e. the food webs seem to be unbalanced (Wilf et al. 2006). Estimates of time-to-recovery of animal groups are also of interest. For instance, North American snakes and lizards took perhaps 10 m.y. to recover their Late Cretaceous diversity (Longrich et al. 2012). A number of common Cretaceous plants failed to survive into the Tertiary, and the familial composition of Early Tertiary forests differed from that of their Late Cretaceous counterparts (e.g. Johnson 2002; Wilf & Johnson 2004). Several clades of heterosporous water ferns failed to cross the boundary, anthough some extant members are known fossil from the Cretaceous (Collinson et al. 2013). However, some evidence suggests that the bolide had relatively slight effect overall. No major plant group is known to have disappeared at the end of the Cretaceous (Nichols & Johnson 2008), and by and large the main pollen genera persisted across the K/T boundary, even if species did not (Tschudy & Tschudy 1986). However, Mander et al. (2010) note that an imbalance between macrofossil (high extinction) and sporomorph (low extinction) across the Triassic-Jurassic boundary can be explained by factors that make the latter record less sensitive. As just mentioned, groups like Annonaceae, Arecaceae, and Araceae are thought to have shown constant diversification rates across the K/T boundary, although some clades show a relatively high diversification rate soon after their origin (literature summarized by Couvreur et al. 2011a). Seed ferns survived until well into the Palaeocene in Tasmania (McLoughlin et al. 2008). For clades that crossed the K/T boundary, features like seed size increased, the average seed mass of angiosperms, initially rather low, increasing markedly in the Tertiary (e.g. Tiffney 1986b; Collinson & van Bergen 2004; Sims 2010). This trend can be seen in Juglandaceae, with many winged disseminules, as well as in Fagaceae, which lack such disseminules (Tiffney (1986a); some Tertiary fruits were fleshy, although rather few in the Palaeocene (Collinson & van Bergen 2004). Seed size shows very interesting variation when examined across all seed plants and considered in a historical context (Eriksson et al. 2000a, b; Moles et al. 2005; Linkies et al. 2010). This increase in seed size may be linked primarily to a change in forest type, now closed and made up of tall trees, and/or to the evolution of the mammals, birds, and bats in particular that dispersed the seeds (e.g. Tiffney 1984, 2004; Eriksson et al. 2000a; Mack 2000; Moles et al. 2005a, b; Eriksson 2008; Dilcher 2010); see Anderson et al. (2011) for the importance of fish as seed dispersers in the Amazon region. Large seeds are common in plants that at least initially grow in shaded habitats, providing reserves for the initial growth of the seedling (Leishman et al. 2000), although they may also be favoured by dry conditions, or soils with low mineral nutrients, etc. (Leishman et al. 2000; Bolmgren & Eriksson 2005). Seed-dispersing animals and the plants they dispersed may have diversified roughly in parallel, although perhaps with something of a lag for the animals (see below: e.g. Tiffney 1984; Wing & Tiffney 1987; Collinson & Hooker 1991; Dilcher 2000; Tiffney 2004; c.f. Herrera 1989). Seed mass of extant angiosperms drops quite abruptly (seven-fold) at the edge of the tropics (Moles et al. 2007: sampling in the tropics not very good), and although the reasons for this are unclear, the efficacy of wind dispersal in the open habitats that are more common there may be involved (Lorts et al. 2008). Trees tend to have larger seeds than herbs, so members of the asterid I + II clade, many of which are herbaceous, tend to have small seeds, while holoparasites and myco-heterotrophs have still smaller dust seeds (Eriksson & Kainulainen 2011). In extant plants, seed size is more or less correlated with genome size (Beaulieu et al. 2007a; Linkies et al. 2010: for a possible negative correlation of genome size and plant size, see Beaulieu et al. 2007b) and more so with plant habit. In general angiosperm diversity in the tropics and warm temperate areas was rather low during the Palaeocene (Wilf 2008). However, by the middle Palaeocene (ca 61 m.y.) vegetation in France was diverse and also supported a diverse assemblage of herbivores, as in a number of sites far distant from the Mexican point of impact of the bolide (Wappler 2009 and references). The bolide event in Colombia is reflected more by changes in ecological structure, less in extinction (De la Parra et al. 2007; see Graham 2010 for the vegetational history of Latin America). Fossils from the Late Palaeocene in Colombia imply that the basic familial composition of the forest was similar to that of current neotropical rainforest, although both plant and herbivore diversity were rather low (Jaramillo et al. 2006). This may reflect a rather belated recovery from the bolide impact and/or that the tropical rainforest ecosystem was just developing (Wing et al. 2009). This Colombian flora studied by Wing et al. (2009) has a very high venation density and is the first fossil evidence of functional equatorial neotropical megathermal rainforst (Feild et al. 2011b). Palaeocene and Eocene Patagonian vegetation was more diverse than its North American counterparts, and herbivory patterns showed similar differences. Thus the diversity of herbivore damage in a fossil flora from the early Eocene in Argentina was appreciably greater than in comparable North American floras (Wilf et al. 2005; Iglesias et al. 2007; Wilf 2008; Wilf et al. 2011). During the early Tertiary, angiosperms with their often dense veinlet reticulum and high leaf specific conductivity (Watkins et al. 2010), in turn associated with high rates of transpiration, may have facilitated the rise to dominance and spread of widespread tropical forest with reliably high rainfall (e.g. Boyce et al. 2008, 2009, 2010; Boyce & Lee 2010). Venation density of angiosperm leaves had increased in the Maastrichtian, an increase associated with increasing maximum photosynthetic rates, and only after this did tropical forests assume a more "modern" physiology (Brodribb & Feild 2009; Feild et al. 2011a, b). Fast decomposition of angiosperm litter, particularly associated with the deciduous habit (Knoll & James 1987, see also below), may also have speeded nutrient cycling and plant growth (Cornwell et al. 2008; Berendse & Scheffer 2009). There were also changes in wood anatomy during this period (Wheeler & Baas 1991); there is more discussion on such matters below. Jaramillo et al. (2010 and references) note that high levels of CO2 and high levels of soil moisture improve the performance of plants when temperatures are high, as earlier in the Tertiary, perhaps also another element in angiosperm success. Menispermaceae are a family today associated with rainforests, and they showed a burst of diversification close to the K/T boundary (Wang et al. 2012). During the Palaeocene-Eocene thermal maximum (PETM) which occurred about 55 m.y.a., some 10 m.y. after the bolide impact, temperatures increased 3-5o (or 5-8o or more - estimates vary) to 31-34o C (Willis & MacDonald 2011). Note that today's l.t.r.f. has a mean annual temperature of ca 27.5oC, and that photorespiration predominates over photosynthesis above 35o (Sun et al. 2012). Over 2,000 gigatons of carbon were released in ca 10,000 years, the whole event lasting a mere 100,000-200,000 years (Zachos et al. 2008; McInerney & Wing 2011). Temperature swings later (at ca 53.5 m.y.) in the Eocene may have been as or even more extreme (Sluijs et al. 2009). Humidity, precipitation and so weathering all increased during this period (Zachos et al. 2001, 2008). In South America plant diversity and origination rates increased at about the time of the PETM, however, there is no evidence of thermal damage to the leaves (Jaramillo et al. 2010), in west-central North America plant diversity and herbivore diversity and activity increased (Currano et al. 2008), and diversity was also very high in Late Paleocene Gulf Coast floras with an increase in pollen diversity of ca 15% then (Harrington & Jaramillo 2007). There may have been major diversification of herbivorous beetles in particular and insects in general (Farrell 1998; Wilf & Labandeira 1999; Wilf et al. 2001; Lopez-Vaaamonde et al. 2006), and Citerne et al. (2010) suggest that this was a period of floral innovation. Evidence for extinctions at about this time is unclear. It has been suggested that the PETM caused some marine extinction, and also shifts in the distributions of both plants and animals, although perhaps little extinction (Wing et al 2005; Willis & MacDonald 2011, but c.f. Mander et al. 2010). In parts of Europe there is evidence for episodic fires in a vegetation dominated by ferns and perhaps Fagales (Collinson et al. 2007). At around this time there is a pronounced (ca 20%) decrease in palynological diversity in the then paratropical Gulf Coast floras (Harrington & Jaramillo 2007). Although temperatures soon moderated, they then became gradually warmer, peaking during the Early Eocene Climatic Optimum of 52-50 m.y.a., when it was much warmer, wetter, and more temperate than it is now (e.g. Greenwood & Wing 1995; Upchurch et al. 2007; Zachos et al. 2001, 2008; Kroeger & Funnell 2011). Unique mixed deciduous broad-leaved and evergreen and deciduous conifer forests grew north of 65-70o N, and these were remarkably speciose considering that it was dark for about a third of the year (Collinson 1990; Jahren 2007 and references); there seems to have been some local endemicity (Harrington et al. 2011). Earlier, Wing (1987) had emphasized the uniformity and homogeneity of broad-leaved evergreen forests at ca 60o N, while Harrington and Jaramillo (2007) noted the mixture of families that are now temperate or tropical in their distribution in floras of the Gulf Coast in the late Palaeocene. In general, extratropical climates showed little seasonality, and this enabled plants which would seem to have mutually exclusive climatic preferences to grow together. Taxa whose ranges are now tropical then had much wider distributions (e.g. Wing 1987; Archibald et al. 2010; Plaziat et al 2001: Nypa; Smith et al. 2008: Cyclanthaceae; Herrera et al. 2011, Stephania; Collinson et al. 2012: survey of the middle Eocene Messel flora). Palm trees grew well inside the Arctic (Eldrett et al. 2009; Sluijs et al. 2009) and Antarctic (Pross et al. 2012) circles, and the pollen diversity in a site from south Ellesmere Island (76o N) was equivalent to current vegetation in the southeastern United States (Harrington et al. 2011). This Arctic flora has been compared with that of the Pacific Northwest, although overall a match, especially in the seasonality of precipitation, with eastern Asia may be closer (Schubert et al. 2012). Similarly, paratropical rainforest was to be found off Wilkes Land in the Antarctic in the early Eocene ca 51 m.y.a. (Pross et al. 2012). Thus it is only in the early Tertiary, and in the Eocene rather than the Palaeocene, that vegetation takes on a more modern appearance, and a closed, multi-layered l.t.r.f. with climbers and a great variety of associated vertebrates and insects appears (e.g. Upchurch & Wolfe 1987; Wing 1987; Eriksson et al. 2000a; Burnham & Johnson 2004; Pennington et al. 2006a; Crane & Carvell 2007: the early Tertiary fossil record; Burnham 2009: climbers; Morley 2000: good general account of rainforest evolution). Tropical forests as we think of them, the "modern archetypal tropical rain forest" of Burnham and Johnson (2004, see their Table 1), with lianes, epiphytic ferns, bromeliads and orchids, and angiosperms with relatively large leaf blades with dense venation and entire margins, thus seem to be a Tertiary phenomenon (Upchurch & Wolf 1987; Schuettpelz 2006; Boyce et al. 2009: Schuettpelz & Pryer 2009; Watkins et al. 20100. Fires decreased, excluded by the closed forest in which there were few shrubs to support fire and where the litter decayed quickly (Bond & Scott 2010; Bond & Midgley 2012); the Australian area may be an exception (He et al. 2011; Crisp et al. 2011). All in all, species diversity of both animals and plants was probably at a maximum in Eocene forests, as it rebounded from the bolide impact, and it has declined since (Archibald et al. 2010). Early Eocene South American fossil floras were notably diverse, even at 47oS in Patagonia, and included lianes, diversity declining only at the end of the Eocene (e.g. Jaramillo et al. 2006, 2010; Herrera et al. 2011; Wilf et al. 2003, 2011); diversity in western North America seems to have been comparable (R. Y. Smith et al. 2012). Although few Eocene leaf remains can be assigned to modern genera (only at the end of the Eocene can this commonly be done; e.g. Wing 1987; Dilcher 2000), and although the effect of the end-Cretaceous bolide impact on angiosperms is unclear, it is clear that important changes in angiosperm ecology and diversity occurred during the end Cretaceous/beginning Tertiary. Southern temperate forests and Mediterranean vegetation are perhaps the best modern analogues of this rather aseasonal early vegetation. Both are notably speciose (Archibald et al. 2010), while Leslie et al. (2012) note that clade age of southern conifers is considerably greater than that of their northern counterparts, perhaps because of the persistence of milder, wetter habitats there (so shades of the early Tertiary) compared to the increased seasonality and climatic fluctuations in the north. Fiz-Palacios et al. (2011) suggest that the rate of diversification of angiosperms declined somewhat in the earlier part of the Tertiary, one decline being at about the end of the Eocene. Indeed, a long-term cooling trend began then. Estimates are of a 30o C or more reduction in the mean annual temperature since the end of the Eocene (Jahren 2007), temperatures dropping 8.2±3.1oC alone in some 400,000 years at the beginning of the Oligocene some 33.5 m.y.a. in central North America, although apparently with little change in precipitation (Zanazzi et al. 2007). The Antarctic ice sheet appeared ca 33.5 m.y.a. at the Eocene-Oligocene boundary (Eldrett et al. 2009 and references) although cooling in the Wilkes Land shelf area and spread of more temperate Nothofagus fusca-type pollen had become evident by the middle Eocene (Pross et al. 2102). Seasonality began to develop in extratropical floras in general at the end of the Eocene (e.g. Wing 1987; Eldrett et al. 2009), although marked seasonality in fossil woods is a Neogene (Pliocene and since - the last ca 23 m.y.) phenomenon (Wheeler & Baas 1993); more or less ring porous woods showed a marked increase from the Palaeocene to the Eocene, and again from the Oligocene to the Miocene (Wheeler & Baas 2011). Along with seasonality, there are suggestions that the latititudinal biodiversity gradient, now so pronounced, with diversity decreasing strongly away from the equator began at about this time (Mannion et al. 2012). There is evidence of increased weathering of rocks at this period and through the later Caenozoic (Pälike et al. 2012). Indeed, a number of plant taxa now restricted to Southeast Asia grew in Europe and North America at various times from the Palaeocene to the Miocene (e.g. Ferguson et al. 1997; Manchester et al. 2009: East Asian endemics), and there were similar changes in the Southern Hemisphere, for example in conifers (Wilf 2012). Tropical floras became less widespread, extra-tropical floras became less diverse and less cosmopolitan (Archibald et al. 2010), and deciduous plants became more widespread. Temperatures in the Oligocene rebounded slightly and oscillated through the Miocene, with an increase in the mid-Miocene ca 16 m.y.a. which was quite warm and wet; subsequently there was further decline (Zachos et al. 2001, 2008; Relallack 2009; Crisp & Cook 2011). The concentration of carbon dioxide in the atmosphere was falling through most of this whole period (e.g. Arakaki et al. 2011); Arctic ice started developing ca 7 m.y.a. (Zachos et al. 2001). Although ecological conditions may still have been rather different from those of today, many fossils even from the beginning of this period are assignable to extant genera and any ecological differences are surely less than when comparing Cretaceous and extant angiosperms (Jaramillo et al. 2006; Mittelbach et al. 2007). In the mid-Pliocene some 3.6-6 m.y.a. temperatures were 2-3o warmer than they are now, again, novel vegetation assemblages developed and there was increased diversity (Willis & MacDonald 2011). The great ecological importance of grasses, including those that carry out C4 photosynthesis, developed only within the last (10-)5 m.y. (e.g. Edwards et al. 2010), although the origin of this trait goes back 20 m.y. or more. The widespread Cerrado vegetation of Brazil developed at about the same time (Simon et al. 2009; Simon & Pennington 2012), as did many clades with succulent plants, whether terrestrial or epiphytic, and these often have CAM photosynthesis (Arakaki et al. 2011). Even if a number of herbaceous groups in particular diversified (e.g. Tiffney 1985a, b????). Magallón et al. (1999) noted that major core eudicot clades like Fabaceae (19,000+ species: e.g. Bruneau et al. 2008b; Bello et al. 2009) and (most of) Lamiales that together represent about 45% of core eudicot diversity appear only in the upper Cretaceous (Maastrichtian) and Tertiary. Diversification of Asteraceae (23,000+ species: K.-J. Kim et al. 2005; Funk et al. 2009c for a summary) is also Tertiary in age. Even in far older clades like Myristicaceae, crown group diversification may also be largely a Tertiary phenomenon (J. A. Doyle et al. 2004, 2008; Scharaschkin & Doyle 2005; Richardson et al. 2004; but c.f. in part Couvreur et al. 2011a, c). Ca 24,440 species of angiosperms are epiphytic (Schuettpelz & Pryer 2009; Zotz 2013), about half being members of Orchidaceae-Epidendroideae (Ramírez et al. 2007; Gustafsson et al. 2010; Conran et al. 2009) and Bromeliaceae (Givnish et al. 2008a) alone, and both of these groups diversified in the Tertiary, along - perhaps - with epiphytic ferns (Dubuisson et al. 2009). Seedless vascular plants seem to be particularly important components of the epiphytic vegetation in the rainforests of the Antopodes and Oceania (Dubuisson et al. 2009). Details of the relationships between groups diversifying in seasonal temperate regions and their tropical relatives have been a matter of speculation for some time (e.g. Bews 1927). Judd et al. (1994) found that the temperate family of temperate-tropical family pairs often arose from within the tropical family, making the latter paraphyletic; the temperate groups tended to be herbaceous, the larger group from within which they arose, woody. Other literature focuses on establishing global - especially latitudinal - patterns of diversity over time (see Mittelbach et al. 2007 for a critical summary), patterns that then can be explained by such things as higher rates of speciation or extinction. The question is, what global patterns of biodiversity can be discerned, and what causes them? (e.g. Kier et al. 2005). In general, plant diversity is broadly correlated with climate (Fischer 1960; Francis & Currie 2003: families!, c.f. Qian & Ricklefs 2004 for problems with distribution maps). There is a connection between diversity and environmental energy variously estimated (and this links with latitude), species richness and the rate of molecular evolution, but the connections are independent (Davies et al. 2004b; Moser et al. 2005; Jaramillo et al. 2006); Allen et al. (2002) suggested that productive environments support more individuals, therefore ceteris paribus there will be more mutations, etc. Wiens and Donoghue (2004) suggest that phylogenetic niche conservatism might contribute to tropical diversity; it has been hard for groups that are tropical in origin to adapt to seasonal temperate climates (and vice versa). In connection with this hypothesis, absence of seasonality, widespread in the Palaeocene-Eocene, but now found mostly in tropical and to a certain extent south temperate areas, may be important (Janzen 1967; Ghalambor et al. 2006). Indeed, B. T. Smith et al. (2012) refined the niche conservatism hypothesis and proposed that in New World vertebrates, at least, families with southern origins were more likely to show niche conservatism than those of northern origin. Southern families have not penetrated the highly seasonal Nearctic, perhaps not simply because there is a smaller southern temperate zone, but because that zone is temperate in a different way than northern temperate zones, while northern families have experienced greater environmental heterogeneity and are often found in both temperate and tropical areas. Evapo-transpiration, topographical diversity, and related factors are also important (Kreft & Jetz 2007). Related to this, Linder (2008) linked the timing of diversification in particular areas to whether or not the local environment had been climatically and geologically stable during the Tertiary. However, teasing apart historical and ecological signals in patterns of plant diversity is not at all straightforward (Ricklefs 2005), and thinking about these patterns in the context of the global ecological patterns established by current angiosperms and their fungal associates in particular which affect soil fertility, carbon content, etc., may provide another way of approaching the problem (see below). There was no simple replacement of gymnosperms by angiosperms. Divergence within extant gymnosperm clades (i.e. genera) of both Cycadales and Pinales is for the most part dated to the mid to later Tertiary (e.g. Oberprieler 2004; Nagalingum et al. 2011; Crisp & Cook 2011; Davis & Schaefer 2011; Leslie et al. 2012). For example, podocarps with flattened foliage units are often shade tolerant and their diversification occured perhaps slightly after the venation density of angiosperm leaves increased - (94-)64(-38) versus 109-60 m.y.a. (Biffin et al. 2011a; Brodribb & Feild 2009; Biffin & Lowe 2011). Extinction may have been higher in gymnosperms than in angiosperms, hence resulting in lower gymnosperm diversification, certainly, gymnosperm clades have longer stems and shallower crowns (Crisp & Cook 2011). However, Brodribb (2011) and Brodribb et al. (2012) emphasized that some conifers, perhaps Pinaceae in particular, are extremely successful in high light but other than high-nutrient conditions. Some other plants now associated with angiosperms diversified in the Tertiary. Most non-angiosperm epiphytes are ferns. One third (ca 3,000 species) of all leptosporangiate ferns are epiphytic (about 10% of all epiphytes) and they may have diversified around the PETM in the early Tertiary (Schneider et al. 2004a, b; Schuettpelz 2007; esp. Schuettpelz & Pryer 2009: Supplemental Tables 2, 3; Watkins et al. 2010). Epiphytic ferns commonly grow on angiosperms and prefer humid conditions (see Watkins & Cardelús 2012 for adaptations of these ferns), an exception, Trichomanes and relatives, had diversified in the early Cretaceous, but they are commonly epiphytic on tree ferns, a very old clade (Schuettpelz 2007; see also Schuettpelz & Pryer 2009; Rothwell & Stockey 2008: early radiations of leptosporangiate ferns). About half - 190/380 species - of clubmosses, Lycopodium s.l., are also epiphytic, and their diversification may have begun in the Late Cretaceous (Wikström & Kenrick 1997, 2001; Wikström 2001). Mosses and liverworts for the most part seem to have undergone bouts of rapid diversification earlier (see above), and Fiz-Palacios et al. (2011, but c.f. Cooper et al. 2012) suggested that there was a slow-down in diversification rates of mosses - and ferns - in the Tertiary. Indeed, much diversification seems to have occured within liverwort families in the Tertiary (Cooper et al. 2012). 7B. Animal Groups. A major question is, is there any relationship between the diversification of animal groups that are now more or less directly dependent on plants for food, etc., and of the plants themselves? The connection between animal and plant can be indirect: That the diversification of orb-weaving spiders, insect-eating bats, stinging wasps, etc., was more or less contemporaneous with that of angiosperms is interesting - they were eating insects, at least some of which were eating plants - but it was probably of little direct effect on seed plant evolution (see also Hawkins & Porter 2003; Penney 2004; J. S. Wilson et al. 2013). Similarly, the fleshy fruit "niche" was exploited by particular groups of flies, particularly by Drosophilinae, and the relationships between particular fruits and flies may be very close (Ashburner 1998: alcohol dehdrogenase in flies; Harry et al. 1996, 1998: fig-breeding Lissocephala). In the rest of this section I will focus on animal groups that are particularly important for flowering plants and in which the relationship is direct. Plant-feeding insects make up at least one quarter of all described species, and over half the beetles (Janz et al. 2006; Farrell 1998; Hunt et al. 2007). There are well over 100,000 species of extant phytophagous beetles in some five clades that eat angiosperms, but initial beetle diversification occured in the Jurassic (Farrell 1998, but c.f. dates; see also Mayhew 2007; Hunt et al. 2007), perhaps first on monocots and then moving on to broad-leaved angiosperms (Reid 2000). About two thirds of these beetles eat only one or a few species of angiosperms, i.e. they are are mono- or oligophagous. Herbivorous beetles and herbivory in particular and insects in general increased with the warming tend of late Palaeocene-Eocene (Farrell 1998; Wilf & Labandeira 1999; Labandeira et al. 2002b; Wilf et al. 2001; Lopez-Vaamonde et al. 2006, Wilf 2008). Kergoat et al. (2005) suggest that diversification of bruchids and Fabaceae may have occurred more or less together; the association between these two is particularly close, some kind of co-evolution. Ants represent only ca 2% of known insects, but they make up one third of insect biomass, and overwhelmingly dominate in fogging samples of rainforest canopies (Davidson et al. 2003; Pie & Tschá 2009). Unfortunately the relative timing of diversification in ants and angiosperms is unclear. Estimates of beginning of crown-group diversification of ants are 176.4-132.6 (Moreau et al. 2006: depends on calibration used) and 143.2-108.6 m.y. (Brady et al. 2006) respectively, extant members of "basal" ant clades living largely underground (Rabeling et al. 2008). Moreau et al. (2006) thought that ant diversification was dependent on the radiation of angiosperms, which had occured by around 100 m.y., lineage through time plots showing a dramatic accumulation then. On the other hand, Pie and Tschá (2009) suggested that the rate of divergence of the main clades was constant, but within these clades diversification rates had varied greatly. Between 100 and 60 m.y. the rise of angiosperm-dominated forests was tracked by ant diversification (Moreau et al. 2006). Most estimates suggest that the ecological dominance of ants began later in the Eocene, 50-35 m.y.a., ants first becoming common in the fossil amber record then (e.g. Grimaldi & Agosti 2000; Moreau et al. 2006; Dunn et al. 2007; Grimaldi & Engel 2005; LaPolla et al. 2013: over 5% of insects). Although many ground-dwelling ants are carnivores, the tree-loving Formicinae and Dolichoderinae are canopy-dwellers and eat plant materials (Rico-Gray & Oliveira 2007). Plant-ant associations evolved in the late Eocene and afterwards, probably not earlier (Grimaldi & Agosti 2000; Dunn et al. 2007); the commonly encountered associations between ants, plants and sap-sucking homopterans (e.g. Ueda et al. 2008) are mid-Tertiary or later. Sugar obtained either directly from the extra-floral nectaries of plants, or indirectly, for example by way of their homopteran associates, is an important food/energy source for many of these arboreal ants (E. O. Wilson & Holldöbler 2005). (The homopterans involved are Auchenorrhyncha, leaf hoppers and spittle bugs, and Sternorhyncha, scale insects and aphids.) The oldest extra-floral nectaries known are on Populus fossils from the Oligocene (Pemberton 1992). Obligate bacterial endosymbionts are well known from homoptera, and members of Rhizobiales are particularly associated with herbivorous ants (Davidson et al. 2003; Russell et al. 2009). Diversification of the ecologically very important herbivores of the New World tropics, the ca 40 species of leaf-cutting attine ants, occured quite recently - various stem group estimates are (16-)13-9(-7) m.y., crown group estimates are (14-)11-8(-6) m.y. (Schultz & Brady 2008). Ants also disperse the seeds of many angiosperms. Elaiosomes, quite commonly found on small seeds or fruits (Beattie 1985; Rico-Gray & Oliveira 2007), vary considerably in their morphological nature and chemistry (e.g. Kubitzki et al. 2011). They provide food for ants which eat the elaiosomes, but not the seeds themselves (c.f. granivorous ants), and aid in the dispersal of plant disseminules and perhaps in the establishment of the seedling. The fatty acids in the elaiosomes that attract carnivorous ants may mimic those in their animal prey, the elaiosomes being "dead insect analogue[s]" (Carroll & Janzen 1973: p. 235; Hughes et al. 1994). Myrmecochory is particularly common in the ground flora of the east North American and European forests (Sernander 1906; Berg 1975; Orians & Milewski 2007; Lengyel et al. 2009, and references), although Türke et al. (2011) suggest that gastropods may also be involved in the distribution of such seeds. It is also common in the Australian and South African floras (Milewski & Bond 1982; Bond et al. 1991). Conservative estimates are that some 11,500 species are myrmecochorous (Lengyel et al. 2009, 2010) and the trait is highly polyphyletic - caruncles have evolved ca 13 times in Euphorbia alone (Horn et al. 2012). Myrmecochorous clades have about twice as many species as their non-myrmecochorous sister clades (Lengyel et al. 2009). Myrmecochory in clades such as Polygalaceae-Polygaleae seems to be linked to their diversification and is a mid-Tertiary phenomenon (Rico-Gray & Oliveira 2007; Forest et al. 2007b; Lengyel et al. 2009, 2010, see also Fokuhl 2008). In addition, perhaps half the species of stick insects (Phasmatodea) lay eggs that mimic seeds of myrmecochorous plants (Hughes & Westoby 1992). The phytophagous beetle sister taxa, weevils (Curculionoidea) and leaf beetles (Chrysomeloidea), include about half of all herbivorous insects. They may have diversified largely in parallel with angiosperms (Farrell 1998), although initially being associated with gymnosperms, diversification beginning there in the Jurassic (e.g. Labandeira et al. 1994; Farrell 1998; Mckenna et al. 2009). However, given the evidence already mentioned for quite recent diversification in some gymnosperm clades and the questionable association between phytophagy, gymnosperms and diversification (Hunt 2007), the story need to be rethought. Indeed, Chrysomelidae may diversify rather later than angiosperms, perhaps (86-)79–73(-63) m.y.a. in the Late Cretaceous-Eocene (Gómez-Zurita et al. 2007; also Winkler & Mitter 2008), and especially in the early Tertiary. Crown-group diversification of major angiosperm-associated weevil clades may have been underway by the Aptian 125-112 m.y.a., with a a "massive diversification" of Curculionidae - ca 90% of all weevils - 112-93.5 m.y.a. during the Cretaceous terrestrial revolution (McKenna et al. (009). Lepidoptera, with ca 160,000 described and perhaps 500,000 total species, are the biggest insect clade almost exclusively dependent on plants, both as adults and as larvae (Powell et al. 1998; Mutanen et al. 2010). Unfortunately, relationships between the main clades are poorly understood, perhaps reflecting very fast initial evolution (Mutanen et al. 2010). Diversification of lepidoptera may have started on Jurassic gymnosperms (Lanadeira et al. 1997), or rather later (Grimaldi 1999). Papilionoidea (butterflies) are well embedded in monotrysian lepidoptera, and Heikkilä et al. (2011) suggested that the main clades [families] within an expanded Papilionidae diverged quickly in the early Cretaceous; clades that represent current butterfly tribes diverged only after the K/T boundary even if family clades are largely of late Cretaceous origin (Wahlberg et al. 2009). Estimates for diversification within clades representing extant subfamilies are after (e.g. Vane-Wright 2004; Wheat et al. 2007; Heikkilä et al. 2011), more or less at (Simonsen et al. 2011, or before (Michel et al. 2008; Pohl et al. 2009: 113-84 m.y.a., gene duplications) the K/T boundary. A question is, were butterflies quite diverse in the Cretaceous, but only a few clades crossed the K/T boundary, or did ecological conditions suitable for diversification of Papilionoidea, i.e. the development of forests with "modern" ecology and composition, occur only in the Tertiary (Heikkilä et al. 2011)? Butterfly (and other herbivore) clades that survived the K/T boundary may initially have eaten several different food plants, but subsequently they diversified on a more restricted set of plants or they shifted their food preferences (Janz et al. 2006; Nylin & Wahlberg 2008; Fordyce 2010). Turning to individual butterfly groups, diversification of of Nymphalidae-Nymphalinae seems to be a post K/T boundary phenomenon, occurring 65-33 m.y.a. (Wahlberg 2006), and the same is true of Nymphalidae-Papilioninae (Zakharov et al. 2004). Diversification may have begun before, as in Pieridae which began diversifying the the Late Cretaceous ([112-]95[-82] m.y.a.: Braby et al. 2006), but again, much speciation seems to have been in the Tertiary (see Simonsen et al. 2011 for a range of divergence times). Caterpillars of these groups tend to show rather high food-plant specificity. Our understanding of the big picture of lepidopteran phylogeny is insufficent to be able to relate it to angiosperm evolution. Overall, there seems to be no simple connection between the diversification of plants and the insects associated with them. Some bouts of insect diversification may have occurred well after the appropriate angiosperm host clades originated, particularly in herbivores (implicit in Futuyma 1983; see Funk et al. 1995; Percy et al. 2004; Lopez-Vaamonde et al. 2006; leaf-mining Gracillaridae; Winkler & Mitter 2008; McKenna et al. 2009; Janz 2011; Cruaud et al. 2012b). Certainly diversification and overall diversity of phytophagous insect groups may increase after they adopt new hosts (Janz et al. 2006); subsequently the relationship may be reversed. Close co-evolution seems to be the exception (but see Kergoat et al. 2005 below) rather than the rule, and is most evident in shallow rather than deep clades (Berenbaum & Passoa 1999 for references; c.f. Farrell & Mitter 1998); looser "co-evolution", with host shifts associated with taxonomy, may be more common (see Futuyma & Mitter 1996). Different kinds of relationships may tend to show different patterns of (co)diversification, relationships in herbivory and parasitism perhaps differing from plant-pollinator relationships. For the latter, see Ramírez et al. (2011), Althoff et al. (2012) and Schiestl & Dötterl 2012); here diversification of plant clades may occur despite (in the context of some definitions of co-evolution) the low diversity of the pollinator. Currently, vertebrates facilitate the wide dispersal of rather large propagules of rainforest trees and often the (cross) pollination of the rather widely dispersed individuals that produce them (e.g. Regal 1977); mammals in particular are also herbivorous. Mammals have a substantial fossil history before the Cretacous, but their diversification in the early Tertiary is particularly notable (Bininda-Emonds et al. 2007; see also Stadler 2011a). Indeed, a recent comprehensive morphological analysis - over 4,500 characters were scored - suggests that crown-group placental mammals are Tertiary in age, age estimates for particular clades being up to 30 m.y. younger than those in earlier studies (O'Leary et al. 2013). For primates, initially diversifying in the arboreal habitat as omnivores (plants and their associated insects), see Sussman et al. (2013). Phyllostomid and vespertilionid bat diversification and that of angiosperms is associated; insect-eating bats (vespertilionids) may have diversified because there were more insects because of the diversity of plants, and fruit-, pollen- and nectar-eating bats (leaf-nosed bats, the phyllostomids) because there were a greater diversity of fruit types and an abundance of flowers (Jones et al. 2005; Teeling et al. 2005). Both frugivory and nectarivory have arisen in parallel, even in New World bats, and some combination of insectivory with these modes of nutrition is common (Datzmann et al. 2010; Rojas et al. 2011). In general, bat-pollinated flowers probably began evolving in the Miocene (Fleming et al. 2009). Crown-group diversification of phyllostomid bats began some time between 43.1 and 33.4 m.y.a. (probably in the late Eocene), with much diversification 26-16 m.y.a. in the late Oligocene to mid-Miocene (Datzmann et al. 2010; Rojas et al. 2011); adoption of a plant diet seems to have accelerated bat diversification rates (Datzmann et al. 2010). Phyllostomid bats are important frugivores in the Neotropics where they specialize on fruits of genera like Vismia, Solanum, and Ficus (Lobova et al. 2009; Mello et al. 2011); these are particularly epiphytic, understorey and early successional plants (Muscarella & Fleming 2008; c.f. in part Mello et al. 2009). Old World pteropodid bats tend to disperse seeds of later-successsional trees, and they prefer fruits of families like Sapotaceae Meliaceae, Arecaceae and Rubiaceae (Muscarella & Fleming 2008). Bats can be very abundant, and New World Taxa in particular are wide-ranging compared to Old World fruit-eating bats (the pteropodids) (Muscarella & Fleming 2008) and their ecological importance in terms of the services they provide plants is considerable (Freeman 2000; Muscarella & Fleming 2008). There are some 39 species of nectar-eating phyllostomid bats, and the ages of crown-group diversification in the two clades to which they belong are in line with those just mentioned (Datzmann et al. 2010). For a comprehensive phylogeny of all birds (Jetz et al. 2012). Radiation of important seed-dispersing birds such as Columbiformes (pigeons) occurred some (63.6-)54.4(-46.1) m.y.a. (95% CI), also in the earlier Tertiary (e.g. Tiffney 1986b; Pereira et al. 2007). Bird pollination is also likely to be a Tertiary phenomenon, with three different groups of birds (Trochilidae, Nectariniidae, and Meliphagidae) predominantly being involved (Cronk & Ojeda 2008); hummingbirds diversified only in the Pliocene (Bleiweiss 1998a; McGuire et al. 2007). Overall, our understanding of the ecological-evolutionary connections between animals, in particular insects, and plants remains unclear (e.g. Futuyma 1983; Janz 2011); there is no simple underlying theory to explain the variety of the interactions. Yet, as Grimaldi and Engel (2005: p. 625) note, "Despite the fact that the mechanism is obscure as to how insects diversified with angiosperms, the overall patterns are extremely clear that the angiosperm radiations had a profound impact on insects, and vice versa." We know little about the details of long-term evolutionary-ecological interactions of plants and the organisms associated with them (see above; Fine et al. 2004 for habitat specialization and herbivore activity in the Amazon, also Janzen 1974a). Furthermore, the sheer complexity of the matrix of defensive compounds inside the plant make simple explanations of the evolutionary dynamics of plant-insect relationships difficult. As Berenbaum and Zangerl (2008: p. 806) note, idiosyncracy is central to the nature of chemical co-evolution, a problem that can only be exacerbated by the difficulty of understanding ecological relationships over time. 8. Flowers, Pollination, and Evolution. 8A. Flowers and Pollination. Most narratives of angiosperm evolution focus on the flower and fruit and their influence on speciation, the success of angiosperms being attributed in considerable part to the evolution of flowers (e.g. Eriksson & Bremer 1992; Dilcher 2000). The flower can be considered a key innovation or a group of innovations, thus Frame (2003) emphasized flexibility in construction of the flowers, the speed of the reproductive cycle, the closure of the carpels, and the fact that flowers are edible hence attracting some kinds of potential pollinators. Floral rewards and how they are offered vary: Some - probably including most early angiosperms - offer only pollen, while various kinds of nectaries are found in many other angiosperms, e.g. septal nectaries in many monocots and receptacular nectaries of one sort or another in core eudicots (see above), oils and fragrances are minor rewards; deceit is surprisingly common. Successful pollination entails the pollinator following a more or less complex and specific set of cues. Pollination, especially by insects, but also bats and other mammals as well as birds, and seed dispersal, especially by mammals and birds, may interact, in that both may increase outcrossing and gene flow in general, and hence speciation (Kay et al. 2006; Kay & Sargent 2009 for a summary). Burger (1981) saw insect pollination as a key to the diversification of angiosperms, insects being able to find isolated plants in small populations, and angiosperms were able to subdivide the environment effectively. Schemske and Bradshaw (1999) in a classic paper discuss possible links between pollinator behaviour and pollination preferences of humming birds and bumble bees as drivers of speciation (see also Gegear & Burns 2007, floral features considered more or less separately), while Pauw et al. (2009) described rather diffuse co-evolution between flies with long probosces and and a group of species with long-tubed flowers (see also Bascompte & Jordano 2007). Adoption of syncarpy seems to be an important evolutionary event (e.g. Friis et al. 2006b). It has evolved seventeen or more times independently, while a compitum, allowing pollen tubes from one stigma to pollinate the ovules in more than one carpel, also evolved in three quarters of these cases (Armbruster et al. 2002). Members of the ANITA grade - perhaps not Nymphaeales - quite frequently have an extragynoecial compitum in which pollination of ovules in more than one carpel from pollen landing on a single stigma is possible (e.g. Williams et al. 1993; Lyew et al. 2007; Williams 2009 - see also Igersheim & Endress 1997; Endress & Igersheim 2000). The development of a style allows competition among gametophytes (Mulcahy 1979) and may also be associated by an increase in size of pollen grains (Roulston 2000 for references). Self pollination is hindered by sporophytic and gametophytic incompatibility (see Ingrouille & Chase 2004), and less effectively by protandry or protygyny (the latter is commonest in members of the ANITA grade and the magnoliids). Closed carpels both protect the ovules and may become much elaborated when the seeds are mature, so promoting dispersal. The evolution of the carpel may have allowed control both over fertilization and allocation of resources to the seed (Lord & Westoby 2012 and references). Endosperm, tissue involved in the nutrition of the embryo and with both maternal and paternal genomes (usually with a diploid maternal and a haploid paternal contribution) is unique to angiosperms, although there is controversy over its origin (c.f. e.g. Friedman & Williams 2004 and Nowack et al. 2007). Why there should be variation in embryo sac development at the base of the angiosperm tree (and sporadically elsewhere, too) that affects the balance of maternal and paternal genes in the parent sporophyte-endosperm-seedling system, is not well understood. However, a higher ratio of paternal genes in the endosperm may lead to more "selfish" behaviour of individual endosperm tissues as they scavenge nutrients at the expense of other ovules in the carpel (e.g. Friedman et al. 2008; esp. Friedman & Ryerson 2009) - hence perhaps the rather low ovule number (per carpel) of many ANITA-grade angiosperms which have exactly this higher ratio. The significance of variation of endosperm development is unclear, and as Olsen (2004: p S215) noted, "In spite of recent progress in understanding angiosperm phylogeny, all of the main questions regarding the evolutionary history of the nuclear endosperm remain unresolved." Angiospermy is also associated with a number of changes in the gametophyte phase of the life cycle, which is usually notably shorter than that of extant gymnosperms. Thus the rate of pollen tube growth in angiosperms is much faster than that of extant gymnosperms - 80-600 µm/hour in ANITA-grade angiosperms (overall 60[Fagaceae]-20,000 µm/hour) versus 10-20(Gnetum) µm/hour in gymnosperms (Hoekstra 1983; esp. Williams 2008, 2009; also Rudall & Bateman 2008). Fertilization occurs within about 24 hours in these angiosperms as compared to seven days - often far more - in most extant gymnosperms (Williams 2008). Speedier pollen tube growth may be helped by the evolution of callose plugs in the tube and a wall made up largely of callose, other apomorphies of angiosperms; gymnosperms lack these plugs and have a cellulose-based pollen tube wall (Williams 2008; Parre & Geitmann 2005: mechanical properties of callose). Although only some development of the female gametophyte development occurs after pollination in Gnetum, the ovule still increases appreciably in size between pollination and fertilization, whereas in angiosperms there is little or no increase (Leslie & Boyce 2012). Furthermore, there is little growth of the ovule after fertilization in most gymnosperms, reserves for the developing ovule having already been sequestered in the female gametophyte. In angiosperm ovules, on the other hand, few reserves are committed to the ovules with their tiny female gametophytes, and ovules abort if not fertlized. After fertilization, however, large amounts of resources can be channelled to the developing embryo mediated by the evolutionarily novel endosperm tissue; it is as if growth of the ovule had resumed (Sakai 2013). Overall, angiosperms tend to become mature at a younger age than do gymnosperms (Bond 1989; Verdú 2002). The whole life cycle is speeded up (Stebbins 1965, 1981), the evolution of carpels faciltating maximum seed production, seed dispersal, and seedling survival (Stebbins 1981). Seedlings of angiosperms grow faster than those of gymnosperms; again, time to maturity is reduced (e.g. Bond 1989; Coiffard et al. 2006). Different pollinator groups have different floral preferences. Adult Lepidoptera prefer to visit radiate flowers, that is, polysymmetric flowers with a definite number signal (e.g. three-merous, five-merous flowers) and that have enclosed nectar (e.g. Leppik 1957). In Apidae, bumble bees (Bombini) in particular appear to have an innate preference for monosymmetric flowers (Leppik 1957; Kalisz et al. 2006; Rodríguez et al. (2004) found that bumble bees preferred monosymmetric flowers, the test was only against asymmetric flowers. Honey bees (Apini) frequent polysymmetric (radiate) flowers with relatively accessable nectar (for a review of the cues used, see Horridge 2009). Bumble bees are effective buzz pollinators, honey bees are not (Goulson 2010). Halictidae-Rophitinae (sister to all other halictids) prefer to visit flowers of asterids, especially those of members of the asterid I clade, although other plants are also visited (Patiny et al. 2008). Similarly, some flower types are particularly distinctive. Thus the buzz pollination floral syndrome has evolved many times, perhaps some 4,000 species of angiosperms, mostly core eudicots, being involved (Buchmann & Hurley 1978; Buchmann 1983). Note that polylectic or generalist bees such as bumble bees visit flowers with complex, often monosymmetric corollas which the animal has to learn to work before visits are effective, while more specialist oligolectic bees prefer to visit shallow often polysymmetric flowers with easily accessible rewards (Wcislo & Cane 1996). Similarly, oligolectic basal megachilids pollinate radially symmetric and sometimes rather large flowers, while more polylectic derived members commonly pollinate monosymmetric Fabaceae and Lamiaceae, or monosymmetric Boraginaceae (Litman et al. 2011; Sedivy et al. 2013), often with keel flowers (for their pollination, see Westerkamp 1997). Early angiosperms may have had rather generalized flowers, and the plesiomorphic condition for pollination specificity in bees seems to be oligolecty; this may have facilitated early angiosperm evolution (Danforth et al. 2006; Sipes et al. 2006; Michez et al. 2008). Floral specialization has increased over evolutionary time, "specialized" monosymmetric flowers in which precise interactions between plant and pollinator are needed for effective pollination becoming more common, even as species of Apidae visit over twice as many families of flowering plants as do those of Halictidae and over five times those of Colletidae (Waser et al. 1996). I will return to these issues later. 8B. Major Monosymmetric and Wind-Pollinated Clades. A number of large clades (2,000+ species each) can be characterised by features that seem likely to affect diversification/speciation, although the lack of firm age estimates for and within these clades remains an obstacle in understanding this. Five of these major clades, Orchidaceae, Zingiberales, Lamiales (at the node [[Calceolariaceae + Gesneriaceae] The Rest]), Fabaceae, and Asteraceae, have a preponderance of members with monosymmetric flowers. Of course, reversion to polysymmetric flowers has occurred, most notably in Fabaceae-Mimosoideae. Together with some rather smaller clades, e.g. Campanulaceae-Lobelioideae, Caprifoliaceae s.l., Lecythidaceae-Lecythidoideae and Iridaceae, these few clades comprise almost one third of all angiosperms. Indeed, diversification in many clades with monosymmetric flowers seems to be greater than that in their sister taxa with polysymmetric flowers (Sargent 2004; Kay & Sargent 2009; c.f. Kay et al. 2006), perhaps because pollinator fidelity or nectar protection is increased. However, as we come to know more about floral morphology and development, a clear definition of monosymmetry has become elusive. From a structural point of view, many flowers are monosymmetric at some stage of their development (Endress 2008a, also 1999, 2001b; see also Characters). How the pollinator approaches polysymmetric flowers may lead to quite precise deposition of pollen on it, e.g. humming birds pollinating Aquilegia (Kay et al. 2006; see also Iridaceae below). Melastomataceae are particularly difficult to categorise, some flowers being clearly monosymmetic, others polysymmetric, and there are all intermediates; this is largely why they are not included in the list below. Many highly reduced flowers are also monosymmetric, not only in Poaceae (see below), but also in the speciose Piperaceae, etc. An inflorescences may be a unit from the point of view of the pollinator and be functionally equivalent to a monosymmetric flower, as in Euphorbia-Pedilanthus, some Proteaceae, etc. On the other hand, many more or less compact inflorescences are functionally polysymmetric flowers. Here the monosymmetric peripheral flowers in Asteraceae, some Brassicaceae (e.g. Busch & Zachgo 2007) and Apiaceae accentuate the functional similarity of the whole inflorescence to a single, polysymmetric flower; the strongly monosymmetric peripheral flowers are the visual equivalent of petals. It is unclear what a simple morphological categorisation like "flowers monosymmetric" might mean functionally. Euglossine bees and bumble bees (see below) in particular are attracted to monosymmetric flowers; Westerkamp and Claßen-Bockhoff (2007) consider such flowers to be the "ultimate response" to bees. Birds also visit monosymmetric flowers, and in the gullet-type ornithophilous syndrome stamens in the mouth of the flowers deposit pollen on the head of the pollinator. Kalisz et al. (2006) suggest that the development of monosymmetric flowers may be linked to the evolution of dichogamy (separation of the time of pollen dispersal and stigma receptivity), in particular, to that of protandry. However, dichogamy is widespread, and even polysymmetric or haplomorphic flowers of ANITA grade angiosperms are dichogamous, being protogynous. There are five large clades with monosymmetric flowers. 1. Orchidaceae (ca 20,000 species) are ground-dwelling or epiphytic and in part myco-heterotrophic herbs of small, sometimes moderate size producing as many as millions of tiny seeds per flower. The tepals are more or less free and the flowers, with their distinctive and complex morphologies centred on the gynostemium (stamens and stigma-style all congenitally fused) and labellum (median tepal of the inner whorl), are often inverted. Deceit pollination is particularly common, but pollinators also visit for pollen, fragrance and nectar. Although the diversity of floral form in Orchidaceae is great, it is attained by variation on a rather limited basic floral theme. 2. Zingiberales (2,100 species) are quite large plants, mostly herbs, of the tropics with large flowers. Their fruits usually have only a moderate number of seeds that are mostly animal dispersed. Flowers in Zingiberales vary considerably in orientation, the parts that are petal-like, number of stamens, etc., and from this point of view are more variable than Orchidaceae. (Note that many taxa in Commelinales, sister to Zingiberales, also have monosymmetric flowers, and it is possible the the common ancestor of the two orders had such flowers.) 3. Core Lamiales (21,000 species) are often more or less herbaceous plants perhaps particularly abundant oustide the tropics, although there are many tropical members; woodiness is more common there. Individual flowers are moderate to quite large in size, each usually producing quite many and small seeds. Although clades like Lamiaceae have only four seeds per flower, they are still quite small; in general seed dispersal is by wind. Most of the monosymmetric 4. Fabaceae (19,400 species, of which 3,300 are in the polysymmetric Mimosoideae) have inverted keel flowers with more or less free petals (Stirton 1981). The plants are either trees of more or less tropical forests, especially those of the neotropics, or widely distributed herbs. Dispersal is either autochorous (ballistic) or animal-mediated; there are rather few seeds per fruit. Many Fabaceae are nitrogen-fixers, and the family is noted for the diversity of secondary metabolites that it produces, sometimes in association with endophytic fungi. Of the smaller but still quite large clades in which monosymmetry predominates, 5. Campanulaceae-Lobelioideae include some 1,200 species of laticiferous herbs or shrubs with slit-monosymmetric flowers that have plunger-type secondary pollen presentation devices. Their dehiscent fruits have many small seeds 6. Caprifoliaceae s.l. comprise some 850 species; the flowers are often rather weakly monosymmetric and the indehiscent fruits have at most few seeds. Ericales include 7. The some 200 species ofLecythidaceae-Lecythidoideae are trees that can be a prominent element in neotropical forests. The polystaminate androecium alone is monosymmetric, the fruit is large, and the seeds are few and large. In 8. Iridaceae, monosymmetry of the flowers of the speciose Gladiolus is obvious. However, from the point of view of the pollinator the flowers of Iris, Moraea, etc., are also monosymmetric; a single Iris flower consists of three strongly monosymmetric meranthia or part-flowers (see also Westerkamp & Claßen-Bockhoff 2007). All told some 750+ species have functionally monosymmetric flowers. The fruits have moderately numerous seeds. 9. Polygalaceae, with some 1,050 species the majority of which are monosymmetric, are phylogenetically close to Fabaceae, although the exact relationships of the two are unclear (see Bello et al. 2009). They have keel flowers that are superficially like those of many Fabaceae, although different parts are involved (Westerkamp & Weber 1999). The fruits usually have few seeds and myrmechory is common. The final clade to be mentioned here is the insect-pollinated 10. Asteraceae (23,600 species). These are mostly herbaceous to shrubby plants with small flowers that are aggregated into capitulae; at least some flowers of each capitulum are monosymmetric and secondary pollen presentation is widespread. Only a single usually quite small seed per flower is produced, and dispersal is often by wind. Each capitulum is functionally a single polysymmetric or haplomorphic flower which produces quite numerous seeds. Asteraceae are also noteworthy i.a. for the diversity of secondary metabolites they contain. Diversification as a possible result of the aquisition of monosymmetry can be studied on much finer evolutionary scales. For instance, Stebbins (1974) suggested that monosymmetry had evolved more than 25 times within angiosperm families, Westerkamp and Claßen-Bockhoff (2007) noted that it was found in 38 families, and in fact it has evolved hundreds of times (see also Endress & Matthews 2006a; Endress 2008a). Of course, understanding just how many origins there have been depends critically on the evolutionary assumptions we make (e.g. Endress 1997a; Donoghue et al. 1998; Reeves et al. 2003; Cubas 2004; Jabbour et al. 2008) and the definition of monosymmetry we adopt. Most of the clades just mentioned are more or less herbaceous. In general, rates of molecular evolution (substitution rates) may be correlated with the rate of speciation, with more molecular evolution occurring in speciose clades (Webster et al. 2003, see also Barraclough & Savolainen 2001), although this is not always the case (Müller & Albach 2010: Veronica). There are also long-standing suggestions of a correlation between the rate of molecular evolution and plant habit: Molecular evolution is faster in herbs/annuals (e.g. M. A. Wilson et al. 1990; Bousquet et al. 1992: esp. chloroplast genes; Gaut et al. 1992: chloroplast rbcL gene, grasses evolve notably faster even than other monocot herbs, 1996; Barraclough et al. 1996: rbcL gene; Andreasen & Baldwin 2001; Soria-Hernanz et al. 2008: ITS, correlation not very strong; Rydin et al. 2009b; Barker et al. 2009; Korall et al. 2010 [ferns]; Müller & Albach 2010; Yue et al. 2010; Frajman & Schönswetter 2011; c.f. Whittle & Johnson 2003: comparisons of branch lengths of species pairs, ?sampling; Gaut et al. 2011: summary). Both chloroplast and nuclear genes show an increased rate of molecular evolution (Gaut et al. 2011), but not all genes are equally affected (Yue et al. 2010). In a series of extensive analyses of both monocots and eudicots, Smith and Donoghue (2008) confirmed that there are usually substantial increases in the rate of molecular evolution in herbs as compared to trees, shrubs, or simply to plants with long life cycles. For instance, within commelinids the clades Arecaceae, Bromeliaceae and Rapateaceae, all with long life cycles, showed a low rate of molecular evolution - and none is very diverse, at least using sister-group comparisons. The cause of the correlation between molecular evolution and life history is unclear, but it is perhaps connected with mutation rate or population size and hence to speciation (Gaut et al. 2011 and references). The evolution of herbs, with small seeds, from trees has been linked with a rise in the speciation rate of the former (Dodd et al. 1999), although Verdú (2002) suggested that is was not so much the tree habit per se that was important, but the associated condition, length of time to maturity. Herbs also show an increased rate of climatic niche evolution (Smith & Beaulieu 2009). To summarize: Much angiosperm diversity, but not comparable biomass production or net primary productivity (see below), is concentrated in groups that are annuals or herbaceous or shrubby perennials and that have animal pollinated flowers; disseminules are small, rarely fleshy (Eriksson & Bremer 1991, 1992), any animal dispersal often being by hooks. Several of the large groups with monosymmetric flowers mentioned above (Lamiales, Asteraceae, Fabaceae) include many such plants. Overall diversification rates/species numbers are high in the asterid I and II clades, particularly in Asterales and Lamiales (Magallón & Sanderson 2001; Magallón & Castillo 2009), although these rates are best attached to particular clades within orders or even families (see the [asterid I + asterid II] clade). Clades in which dioecy predominates are not notably speciose (Heilbuth 2000; Vamosi & Otto 2002; Kay et al. 2006, etc.). Dioecious plants tend to be woody, wind pollinated, and to have small flowers (for the wind pollination syndrome, see Linder 1998). If insect pollinated, the floral displays tend to be dimorphic, those of the staminate plants being showier and so more visited; extinction is thus perhaps more likely (but c.f. Amborella!). Clades in which wind pollination predominates are also usually not notably speciose; the adoption of abiotic pollination is often associated with a decrease in speciation rate (e.g. Dodd et al. 1999). A clear exception here is Poaceae, 10,050 or so species of largely herbaceous wind-pollinated plants with single-seeded fruits (in most species the flowers can be categorized as being reduced-monosymmetric). Cyperaceae-Juncaceae, another clade of herbaceous, wind-pollinated plants with more or less reduced flowers and also often with single-seeded fruits, contains about 4,800 species. Fagales include about 1055 species. They are nearly all trees, they are monoecious, the flowers are much reduced, the male flowers being catkinate, the ovary is usually inferior, and the fruits are often quite large and always one-seeded. Kay and Sargent (2009) noted that Poaceae and Cyperaceae/Jumcaceae were exceptions to the rule that animal pollination led to an increase in speciation rate, being about seven times more diverse than their animal-pollinated sister clades; however, the mostly animal-pollinated Cucurbitales, probably sister to Fagales, has ca 2,300 species. In wind-pollinated angiosperms there has been selection for numerous small carpellate flowers, and this to a certain extent incidentally also involves a reduction in ovule number per flower - most wind-pollinated taxa have few to a single ovule per flower and single-seeded fruits (Friedman & Barrett 2008, 2011). However, Taylor et al. (2012) suggest that in Fagales, at least, the evolution of monospermous fruits occurred before the evolution of wind pollination. But what is known about the relationships of the features mentioned to the diversification of the clades that posess them? Using Poaceae as an example, we can see how complex the question can be. Are Poaceae diverse, and why? - or what should the question be? A series of points: 1. The first three clades of Poaceae that are successively sister to the remainder contain some 26 species out of the 11,000+, and these three "basal" clades are forest plants (e.g. Givnish et al. 2010b). 2. Many bamboos are woody and with a distinctive, synchronized monocarpic flowering habit and are arguably ecologically distinct from the rest of the family. 3. Poaceae-Poöideae are noted for their association with endophytes, an association that could be ca 40 m.y. old (Schardl et al. 2004). The presence of these endophytes affects the palatability of foliage to herbivorous mammals and of seeds to granivorous birds, and animals eating the infected material may not thrive. The level of aphid infestation and that of their parasites and parasitoids, and even the pattern and rate of decomposition of dead grass, are also affected (e.g. Madej & Clay 1991 - birds; Omacini et al. 2001 - aphids; Lemmons et al. 2005 - decomposition). A variety of alkaloids, including loliine (pyrrolizidine) and ergot alkaloids, are produced by the fungi; the distinctive loliine alkaloid is primarily active against insects (Schardl et al. 2007). Various aspects of root growth may also be affected (Sasan & Bidochka 2012). 4. Grasses are well known for the diversity of silica bodies in their leaves, and these play a role in protection against herbivory, while silicon concentration itself is correlated with the rate of breakdown of plant tissues, and so nutient cycling (see silica). 5. About 75% of the PACMAD clade, some 4,500 species, has C4 photosynthesis (Sage et al. 1999; Grass Phylogeny Working Group II 2011), and are ecologically very distinctive (see below). C4 plants tend to be less attractive to herbivorous animals because of their lower nitrogen concentration and greater amount of fibrous tissue (Caswell et al. 1973). The rise and spread of C4 grasses with their silica-rich tissues in the early Miocene may have been followed by the radiation of grazing mammals such as horses with hypsodont teeth that could deal with such refactory plant material (Thomasson & Voorhies 1990; Retallack 2001; Keeley & Rundel 2003). However, the relation of tooth morphology and silica content of grasses is questionable (Sanson & Heraud 2010), and although prairie grasses expanded in Nebraska in the Early Miocene ca 23 m.y.a., hypsodont ungulates were already around by then (Strömberg 2004). This leads to two sometimes overlooked issues. First, determining exactly which clades are speciose/diversifying rapidly is critical. Second, we often think of the evolution of angiosperms as being largely the consequence of the evolution of flowers (and fruits), diverse floral and fruit form representing adaptations to pollination and fruit dispersal, ensuring reproductive isolation, etc.; flowers allowed greater speciation rates (e.g. Hickey & Doyle 1977). This may well be true - there are many angiosperms, and floral variation is often important in distinguishing between species - but there have also been more physiological changes that have profoundly affected the climate of the earth and the ecology and evolution of angiosperms. It is not simply species numbers alone that matters, but also what species "do", their roles in the ecosystem (e.g. Bengtsson 1998). Some clades seem to have ecosystem effects far beyond the numbers of species they include; see also "The Eco-Physiological Context of Angiosperm Evolution" and especially "Asymmetries in Evolution". [The rest of this section not integrated] The role of genome duplication (polyploidy), which has ocurred many times and at all levels of the tree (see de Martins et al. 2006; Soltis et al. 2009; Duarte et al. 2010, and others), in faciltating diversification by allowing the subfunctionalisation and neofunctionalisation of genes, the evolution of novel regulatory pathways, and other changes, is unclear (e.g. Mayrose et al. 2011); certainly, duplication occurs in gymnosperms, too, even if the chromosome numbers there are low, and also in other land plants. Species-rich clades and genome duplications have been associated, Soltis et al. (2009: p. 336) linking "a dramatic increase in species richness" in Poaceae, Fabaceae, Brassicaceae and Solanaceae with genome duplications there, although as van de Peer et al. (2009a) and others have pointed out, duplication and diversification may not be particularly closely linked in time. Fawcett et al. (2009) dated a series of genome duplications within angiosperms to about 70-57 m.y.a., around about the time of the bolide impact, suggesting that these palaeopolyploids were at a selective advantage because of their hybrid vigour, also having extra genes/alleles available for selection (see also Crow & Wagner 2006 and references; van de Peer 2009a; Franzke et al. 2011). Genome duplications could reduce the probablity of extinction by increasing environmental tolerance and genetic variation, while individual mutations would be less likely to have an immediate effect. Note that Wood et al. (2009) suggest that polyploidy affects primarily cladogenesis, less the diversification rate of those clades; polyploidy may usually be an evolutionary dead end, with recently-formed polyploid plants speciating less and in particular showing higher extinction rates than diploids (Mayrose et al. 2011). Indeed, immediate connections between gene and/or genome duplication and diversification of angiosperms are unclear (see also Schranz et al. 2012: effects delayed). It has been suggested that trees have a distinctive evolutionary rhythm, speciating rather slowly. In any one species the number of individuals may be quite large, and although they may be rather dispersed they are long-lived, the species themselves also being rather long-lived (Petit & Hampe 2006). However, in the fire-prone Mediterranean ecosystem neither diversification nor molecular evolution differed between seeders and resprouters, two "strategies" allowing plants to survive fires, although seeders under some scenarios should have shown more diversification (Verdú et al. 2007). There is a connection between large seeds, fleshy fruits, and the arboreal habit, although exactly what drives this association is unclear; the ecosystem dynamics of the Cretaceous and Tertiary (Tiffney 2004: see above) provide the context for this. The acquisition of fleshy fruits is not linked with notable increases in diversification of clades with them (Bolmgren & Eriksson 2010 and literature; c.f. Eriksson & Bremer 1991). In general, major shifts in seed mass are rather strongly correlated with changes in life form/plant habit (Eriksson et al. 2000a; Moles et al. 2006a, b). Chanderbali et al. (2009, esp. 2010 and references), promote a fading borders/sliding boundaries model of floral evolution (see also Thiessen & Melzer 2007), and find that the expression of genes that are quite tightly linked to particular floral whorls in eudicots show much less specificity in expression in more basal angiosperms (they studied Lauraceae and Nymphaeaceae). As gene expression is canalized, distinctions between different kinds of floral organs become sharper. Colouring of the corolla in particular, in terms of pigment type, amount, and pattern of deposition, seems to be under the control of a small family of regulatory genes in a diverse set of angiosperms (Schwinn et al. 2006). 9. The Eco-Physiological Context of Angiosperm Evolution. Some of the distinctive vegetative changes that were evident in the leaves of early angiosperms when compared with those of other vascular plants (e.g. Hickey and Doyle 1977) can now be linked with physiological changes that in turn may have facilitated the spread of the l.t.r.f. habitat in which much angiosperm diversity is now to be found and are also implicated in the long-term decline in atmospheric CO2 concentration that characterises the Tertiary. These changes affect the rate of photosynthesis, nutrient cycling and acquisition, silcate breakdown and rock weathering, and the like (e.g. Knoll & James 1987; Volk 1989). There are a number of feedback loops, many positive, implicated in changing climates and CO2 concentration (e.g. Berner 1999; Beerling 2005a; Beerling & Berner 2005). These eco-physiological changes have allowed angiosperms to grow in a great diversity of environments, including large areas of ever-wet forests, and they provide the basic ecological space for features associated with pollination and seed dispersal to interact with aspects of the biotic and abiotic environment (see also Boyce et al. 2010; Marazzi & Sanderson 2010). Despite the far-reaching effects of some of these changes, our understanding of the eco-physiological dimension of angiosperm evolution was for a long time rather poor. However, the situation is now completely changing (Feild & Arens 2007 for a good introduction, see also Internat. J. Plant Sci. 173(6). 2012. for useful articles). Seed plants have changed the global environment (e.g. Feild & Edwards 2012). But this is just the beginning. Add to this the interaction of plants with their fungal associates, both ecto- and endomycorrhizal and endophytic, the bacteria associated with them, the evolution of lignin-decomposing fungi, and the effect of all these on mineral weathering in rocks, soil structure, on carbon sequestration, and on nutrient cycling. Indeed, individual plants being best thought of as composites or chimaeras (e.g. Herre et al 2005; Taylor et al. 2009; see Beerling 2005a for vascular plants in general). The physiological-ecological context of angiosperm evolution is very complex. As background, remember that the climate in the Late Jurassic-Early Cretaceous was dry - certainly Pangea had a notably dry interior - but continents were drifting apart, and sea levels were rising. CO2 concentrations were still high, perhaps 3,500-5,000 ppm in the early Cretaceous 135-100 m.y.a., since when they have declined - with the odd hiccup (Beerling & Franks 2010). There may have been a particularly abrupt decrease in the middle of the Cretacous (Feild et al. 2011b; Barclay et al. 2010), while concentrations briefly spiked at a high of over 1,200 ppm at the PETM (see above). During the recent glaciations they dropped to 180-190 ppm, as low as any during the whole period of land plant evolution (Zachos et al. 2008; Gerhart & Ward 2010; Boyce et al. 2010). 9A. Venation Density, Photosynthesis, and Climate. During the 200+ million year existence of land plants with a dominant sporophytic generation prior to the evolution of flowering plants venation density held largely constant despite considerable fluctuations in atmospheric carbon dioxide concentrations (e.g. Boyce et al. 2010; Lee & Boyce 2010; Boyce & Leslie 2012 for a summary), although stomatal density fluctuated inversely to changes in CO2 concentrations. There seem to have been no major swings in productivity of these plants despite these major changes in CO2 concentration (Boyce & Zwieniecki 2012). Venation density in non-flowering plants continued to hold steady through the Cretaceous (Feild et al. 2011b). Importantly, both extant members of the ANITA grade and Chloranthaceae as well as fossils from the first ca 30 m.y. of the angiosperm record have similar venation densities of around 2.43 mm mm-2 (Feild et al. 2011b: post Hauterivian), and they also show lower CO2 exchange than most magnoliids and basal eudicots (Feild et al. 2011a). These ancestral angiosperms may have had chloranthoid teeth and guttated, but they are likely to have had low drought tolerance (Feild et al. 2011a, c); the leaves also had large and distant stomata, often lacked any palisade mesophyll tissue, and the abaxial surface reflected light back inside (Feild & Arens 2007). The venation density of angiosperms other than the ANITA grade and Chloranthaceae, as well as other shade demanders, doubled at around 108-94 milliion years ago (Feild et al. 2011b), and only with the increase in density did productivity increase (Boyce & Zwieniecki 2012). This increase greatly reduced the main element in the resistance to water flow through the plant, that is, passage through the mesophyll (Sack & Holbrook 2006). Increased vein density came at a cost of increased carbon allocation, although this was partially offset by vein tapering and the high density of minor veins (McKown et al. 2010; Beerling & Franks 2010). These changes allowed an increase in stomatal conductance which in turn can be linked to a higher maximum photosynthetic capacity - with a three-fold increase in venation density, there is a 178% increase in maximum photosynthetic CO2 uptake (e.g. Brodribb et al. 2007; Brodribb & Feild 2010; Feild et al. 2011a; Roth-Nebelsick et al. 2001: vein architecture; McKown et al. 2010: leaf hydraulics). Furthermore, the water potential of angiosperm leaves can decrease 50% before stomatal closure occurs, so allowing maximum leaf hydraulic conductivity to persist in dry conditions, whereas in ferns closure occurs before there is any decrease (Brodribb & Holbrook 2004). Increased transpiration that results from increased stomatal conductance will also promote evaporative leaf cooling (Hetherington & Woodward 2003; Boyce & Lee 2010), perhaps important at times like the PETM when temperatures globally were very high. Interestingly, trees have small, dense stomata when compared with shrubs and herbs (Beaulieu et al. 2008: n = 101). Areas with ever-wet tropical humid climates seem to have been rather restricted in the Cretaceous (e.g. Boyce et al. 2010; Boyce & Lee 2010; Feild et al. 2009a). However, increased transpiration may have helped to drive the spread of widespread tropical forest with reliably high rainfall (e.g. Boyce et al. 2008, 2009, 2010). Thus simulations in which the Amazon rain forest is replaced with non-angiosperm vegetation decreased the extent of ever-wet rainforest there by about 80% (Boyce & Lee 2010; Lee & Boyce 2010). As Boyce et al. (2010) note, the extent of rain forest in other parts of the tropics shows less change in such simulations, but this might have been different under conditions earlier in the Tertiary; the elevation of large areas of continental Africa had not yet occurred, continents were in different positions, etc. The spread of perhumid conditions in which large angiosperms dominate may have selected against drier, rather small stature angiosperm forest subject to frequent fires; fires were widespread in the Cretaceous, but decreased notably in many parts of the world from the mid Palaeocene to the Pliocene (Bond & Scott 2010; Belcher et al. 2010b; Bond & Midgley 2012), although Australia may be an exception (e.g. Crisp et al. 2011). Much woody angiosperm diversification has been in rainforests, and epiphytes, an appreciable component of angiosperm diversity and often herbaceous, are abundant there (Feild et al. 2009a; Boyce et al. 2009, 2010; Boyce & Lee 2010; Boyce & Leslie 2012). Menispermaceae are a family today common in l.t.r.f., and they showed a burst of diversification close to the K/T boundary (Wang et al. 2012). Finally, Boyce and Leslie (2012) suggest that the high assimilation rates facilitated hy high leaf density may also, in conjunction with a shortened life cycle, etc. (e.g. Williams 2012), enabled the evolution of annual herbs, a life form exceedingly uncommon in groups, fossil or extant, other than angiosperms. 9B. Vascular Evolution. Before discussing the evolution of angiosperm vasculature, in which the evolution of vessels plays a large role, it is worth noting that the morphological distinction between vessels and tracheids can be very hard to make (e.g. Carlquist 2012). Early angiosperms were smallish, sympodial trees that were rather tolerant of shaded and disturbed conditions and that grew in humid more or less tropical conditions (Feild & Arens 2005). The ecological context for the early evolution of vessels is provided by living members of the ANITA grade other than the aquatic Nymphaeales (Feild 2005). Of extant angiosperms that are perhaps anatomically and ecologically similar to the first angiosperms, Amborella lacks much in the way of obvious vessels (Feild et al. 2000b; c.f. Carlquist 2012), and the acquisition of vessels in Nymphaeales may be independent of that in other angiosperms (e.g. Schneider & Carlquist 2009). Although individual vessels in both magnoliids and ANITA-grade angiosperms may be more effective in transmitting water than tracheids, on a xylem cross-sectional area basis plants with such vessels may have a hydraulic efficiency similar to that of tracheid-bearing gymnosperms (Sperry et al. 2006; Feild & Holbrook 2001; Hudson et al. 2010). Even although tracheids in conifers are short and have end walls, the overall hydraulic efficiency of plants with such tracheids is higher than might be expected because of the very low resistance to water flow of the margo-torus pits. The central torus may block the pit if needed, yet the fibrils in the margo are widely spaced compared with those in angiosperm pits and so allow water to flow through them more easily (Pittermann et al. 2005; Sperry et al. 2007; Hacke et al. 2007; Hudson et al. 2010). Furthermore, the resistance to water flow of the scalariform perforation plates of early-evolving xylem is higher than had been estimated (e.g. Christman & Sperry 2010). Some palaeozoic medullosan seed ferns, especially taxa like Medullosa, had long, wide tracheids that probably had high water conductivities like those of some angiosperms with vessels (J. P. Wilson & Knoll 2010); ferns in general have wide and long tracheids with surprisingly high transport rates (Pittermann et al. 2011). Indeed, vessels in magnoliids and ANITA-grade angiosperms are rather different from those prevalent in core eudicots (Hacke et al. 2007; Sperry et al. 2007), being short, not very dense, with scalariform perforations, having intertracheidal pit resistance lower than that of intervessel pits, etc. Vessels may have been of functional value initially because heteroxylic wood allows the specialization of cells in the xylem for support, storage, etc., the heteroxylly [sic] hypothesis (e.g. Sperry et al. 2007; Hudson et al. 2010; J. P. Wilson & Knoll 2010). Indeed, the avoidance of cavitation, air bubbles developing in the cells, may have driven the early evolution of vessels (Sperry et al. 2007; Hacke et al. 2007; Philippe et al. 2008; Brodribb et al. 2012: angiosperm:gymnosperm comparisons). Vessel conductance increases substantially when the peforation plates become simple and vessels themselves become long (see e.g. Christman & Sperry 2010; Hudson et al. 2010; Feild et al. 2011c). There were also changes in the Specific Root Length index, a measure of root length/unit biomass. This seems to have increased, i.e. roots got thinner and their hydraulic capacity increased (Comas et al. 2012). Evolution of the whole vascular system, from root to stem to leaf, was slow, but eventually wide vessel elements with simple perforations, the vessels being well over 10 cm long became an integral part of an efficient water transport system; vessels cannot be interpreted simply as a key innovation and their evolution may have been a rather protracted process (Feild & Arens 2007; Feild & Wilson 2012). Less is known about the functional/ecological significance of differences in the phloem of angiosperms and gymnosperms. Even if some differences between sieve tubes (angiosperms) and sieve cells (gymnosperms) may be somewhat over-emphasised - the nucleus in both may be non-functional, even if they differ in how they become non-functional - they do have different sieve plate morphologies, occlusion mechanisms, and ontogenetic/functional associations with neighbouring cells (e.g. see Behnke 1986; Schulz 1992). Other variation in plumbing includes that in the water supply to the flower. The large flowers of at least some magnoliids may obtain their water through the xylem, whereas smaller flowers, as in the core eudicots, may be hydrated primarily via the phloem (Feild et al. 2009a, b, but sampling). There is also substantial variation in phloem pressure and phloem loading in angiosperms, and active phloem loading seems to be most common in the predominantly herbaceous [asterid I + asterid II] clade; a variety of selective advantages for active loading can be suggested (Turgeon 2010b; Fu et al. 2011: see Garryales). Passive loading, with associated high sugar concentrations in leaf cells, may be correlated with the woody habit, and one kind of active loading involving the synthesis of raffinose family oligosaccharides is not connected with plant habit, but perhaps rather with climate (warmer: see Davidson et al. 2010). Interestingly, woody plants that have active phloem loading are usually asterids (e.g. Buddleja, Catalpa, Ilex, Syringa), while herbs with passive transport are members of the predominantly woody rosids (e.g. Rosaceae, Peaonia, Lythrum) - although Saxifraga, an herbaceous rosid, has active phloem transport, while the woody Cercis and Styrax also have active loading (Rennie & Turgeon 2009; Fu et al. 2011). However, the situation is a little confusing since the classifications of phloem transport types in Davison et al. (2011) and Fu et al. (2011) are somewhat different; I have not yet integrated them. 9C. Wood and Litter Decay. Another element to consider is litter and wood breakdown, as well as their loss by burning (Cornwell et al. 2009). About 30% of the organic carbon in the biosphere is currently locked up in lignin (Boerjan et al. 2003). Factors like leaf mass per area (MA, the inverse of specific leaf area [SLA], leaf area to dry mass, cm2 g–1) and primary and secondary venation type have been variously linked with rates of photosynthesis, plant growth, litter decay, nitrogen content, and nutrient cycling. However, there is much within-community variation in such features in angiosperms and any phylogenetic signal in such correlations is not well understood (e.g. Cornwell et al. 2008; Wieder et al. 2009; Walls 2011). Both low MA and high amounts of nutrients in litter, features of angiosperms, are implicated in speedy litter breakdown. Angiosperm floras in the Cretaceous (Potomac, 110-105 m.y.a.: Royer et al. 2007) and Eocene (49-47 m.y.a.: Royer et al. 2010) had a low leaf MA, under 100g/m2; the three gymnosperm plants in the former flora had a mean of 291 g/m2. Even contemporary tropical non-riparian lowland rainforest may have only a moderate MA, e.g. ca 198 g/m2, as on Barro Colorado Island (Royer et al. 2010), and extant gymnosperms, like the extinct gymnosperms just mentioned, have a lower SLA than do angiosperms (Berendse & Scheffer 2009 and references). However, MA per se is unlikely to have been the only factor speeding breakdown of angiosperm remains. Although angiosperm woods are on the whole denser than gymnosperm woods, they, too, decompose faster (Weedon et al. 2009). Brown rot fungi, which can barely degrade lignin, are more common in conifer forests than lignin-decaying white rot fungi (Boddy & Watkinson 1995). Decay is affected by the composition of plant parts. The lignin content of angiosperms is about 20% lower than that of gymnosperms (Robinson 1990); indeed, denser gymnosperm woods have proportionally still more lignin and less nitrogen, while the reverse relationship holds in angiosperms (Weedon et al. 2009). In general, both lignin and polysaccharide content are negatively correlated with the rate of litter breakdown (Cornwell et al. 2008); Martínz et al. 2005: decomposition of lignocellulosic compounds). Furthermore, the syringyl-rich lignins that characterise many angiosperms are more easily decomposed by fungi than the guaiacyl-rich lignins of other seed plants (Ziegler et al. 1985), and angiosperm leaves, litter and wood all have more nitrogen and phosphorous (on a %age basis) than do those of gymnosperms (Cornwell et al. 2008; Weedon et al. 2009). However, overall patterns of wood decomposition vary in detail, and local heterogeneity in decay rates depends on the decay organisms and tree species, and even on the age of the tree (Weedon et al. 2009). The particular factors reponsible are not well understood (Weedon et al. 2009) and the chemistry of woods is complex (e.g. Kögel-Knaber 2002). In any event, litter from extant ferns and fern allies and bryophytes is slow to decompose compared to that of gymnosperms and especially angiosperms (Cornwell et al. 2008). The litter of deciduous angiosperm trees decomposes faster than that of evergreens, angiosperm wood faster than gymnosperm wood, and the litter of angiosperm forbs in particular decomposes faster than that of any other group of land plants (Cornwell et al. 2008; Weedon et al. 2009) - note that these more easily decomposable leaves are likely to be more palatable to insects, too (see below). Graminoid litter - presumably mostly Poaceae and Cyperaceae - decomposes more slowly than that of forbs (Pérez-Harguindeguy et al. 2000; Cornelissen et al. 2001; Cornwell et al. 2008), indeed, graminoid lignin is somewhat different in composition from other lignins, having an appreciable amount of p-hydroxyphenyl units and being low in nitrogen which is removed before the leaf dies (e.g. Cornelissen et al. 2001; Wedin 1995); roots of Poaceae also decompose more slowly than those of other plants (Birouste et al. 2012: sample small, Mediterranean). There is also a negative correlation between litter longevity and silcon concentration in tissues; Poales, and especially Poaceae, have a high silcon concentration, and this is especially high in the annual species (Cooke & Leishman 2011b). UV light also decomposes lignin (Austin & Ballaré 2010). Finally, mean annual precipitation, which, as we have seen, can be affected by angiosperm transpiration, and temperature are also positively correlated with litter and wood turnover and so with the release of the nutrients they contain (Yin 1999; Weedon et al. 2009; Wieder et al. 2009). Low rates of litter decay (accompanied by high MA values) are features of both gymnosperms and angiosperms that are able to grow in stressful, nutrient-poor environments (Berendse & Scheffer 2009). Ferns, gymnosperns and lycophytes tolerate nutrient-poor but mineral-rich conditions, perhaps the ancestral conditions for many of them (Page 2004). The high photosynthetic rates of angiosperms allow high growth rates and the nutrients that they need will be released quickly by the decay of their litter; angiosperms may have been able to utilize any flushes of nutrients produced by litter and wood breakdown, they scavenge nutrients effectively (Berendse & Scheffer 2009). In addition, the disturbed habitats that angiosperms may early have favoured are likely to have had elevated levels of nutrients (Berendse & Scheffer 2009). If early angiosperms were pioneer plants, they might be able to tolerate high herbivory because they had metabolically cheap, rather thin, rapidly expanding leaves with a low amount of fibres and low concentrations of secondary metabolites like terpenoids, phenols, and tannins; their high quality habitat allowed rapid growth and low defence (see e.g. Bond & Scott 2010), and their whole reproductive cycle was relatively short (e.g. Verdú 2002; Williams 2008, 2009). Extant angiosperms with the highest leaf venation densities are woody pioneers (Feild et al. 2011b), while ectomycorrhizal plants have a lower rate of litter decay than endomycorrhizal (see below). It is not only the amount and rate of decay that matters, but its seasonality. In evergreen plants, whether angiosperm or gymnosperm, nutrient cycling is gradual, nutrients being released throughout the year and tending to be taken up by the plants again. In deciduous species, however, nutrients become available in flushes, and some are lost to the ecosystem, and this will increase weathering (Knoll & James 1987). Litter decay results in the release of large amounts of CO2, angiosperm growth removes CO2. CO2 in the soil increases biotic weathering and removes carbon from the terrestrial system (see below). Fire is also very important (Bond et al. 2010). Brener (2003) noted that rocks rich in organic matter derived from plants are particularly prominent in the mid Cretaceous 120-90 m.y.a. to the Palaeocene. Substantial amounts of organic matter may be converted to inertinite, charcoal from fires in mire systems and that is found through the Cretaceous, but less since (Scott & Glasspool 2006). Indeed, the life history characteristics of early angiosperms may have encouraged fires, which, however, were unable to burn closed angiosperm forests when these finally developed (Bond & Midgley 2012). Fires were common through the Cretaceous, but then dropped precipitously, there was a small peak in the Oligocene but considerable increases in the last 10 m.y. (Bond & Scott 2010; Belcher et al. 2010b). Fires cause the release of CO2 into the atmosphere, on the other hand, substances like inertinite are highly resistant to decay, so sequestering carbon. 9D. Ectomycorrhizae and Their Associates. Here the focus is on ectomycorrhizae (ECM) and ericoid mycorrhizae (ERM). There are perhaps 2,500-3,000 species of ECM seed plants, while ERM account for another 4,000 species and orchid mycorrhizae (ORM) over 22,000 more (Brundrett 2009; see also Smith & Read 2008), although Rinaldi et al. (2008) estimate that there are 8,000 ECM species. Ca 7,750 described species of fungi, but probably many more (20-25,000?), are involved (Blackwell 2011; esp. Rinaldi et al. 2008); impressive single-site diversity of such fungi has been documented (Horton & Bruns 2001: examples mostly Pinaceae-dominated forests). There are many more species of ECM fungi than of ECM plants, although the relationship is reversed in Ericaceae and Orchidaceae (Rinaldi 2008). However, ECM-dominated communities are not notably diverse, in part perhaps because of the dearth of readily available nutrients (L. L. Taylor et al. 2009 for literature; see below). ECM taxa have very clumped phylogenetic distributions (e.g. Alexander & Lee 2005), the ecologically most important ECM species being found in perhaps five main clades, Dipterocarpaceae/Sarcolaenaceae/Cistaceae, Fabaceae-Detarieae, Fagales, Pinaceae. These clades, along with the ERM Ericaceae, can all dominate the communities in which they grow, whether tropical or temperate. Such communities are especially prominent in boreal forests and tundra, (cool) temperate and tropical montane habitats, but include West Malesian dipterocarp forests, African Miombo, Mopane and Sudanian forests, parts of the Guineo-Congolian rainforest, etc. (e.g. Hart et al. 1989; Malloch et al. 1980; White 1983; Safer 1987; Sanford & Cuevas 1996). ECM Ericaceae are very common in heathlands world-wide (Read 1996), including alpine and arctic tundra (Jonasson & Michelsen 1996; Michelsen et al. 1998), in montane shrubberies especially in the northern Andes, parts of the eastern Himalayan-Yunnan region, and Malesia, and in heathlands of southern Africa and Australia. Tundra alone occupies ca 8% of the earth's surface and five of the seven most important biomass accumulators there are ECM or ERM (Gardes & Dahlberg 1996). Boreal forests occupy ca 17% of the land surface (Lindahl et al. 2002), and there the trees, predominantly Pinaceae and some Salicaceae and Betulaceae, are all ECM while ERM Ericaceae often dominate in the understory (e.g. Villareal et al. 2004; Vrålstad et al. 2002; Vrålstad 2004; Kranabetter & MacKenzie 2010). Detarieae-dominated forests occupy millions of square kilometres in Africa. The map show areas where ERM Ericaceae (olive), ECM Pinaceae (red), and Fabaceae-Detarieae communities (green) are particularly common (from Specht 1979; White 1983; White et al. 2000; Andersson 2005 - in progress), while biomass estimates for some of these communities are given below. Many ECM plants have a syndrome of ecological characteristics: they are trees, often abundant, mast fruiters, and with large seeds; the soils they grow on are poor, humus accumulates, etc. (e.g. Connell & Dawson 1989; Richards 1996; Torti et al. 2001). Fabaceae-Detarieae also have these features, but not all Fabaceae that do are ectomycorrhizal. ECM/ERM plants from cooler areas like Pinaceae, Ericaceae, Salicaceae, and some Betulaceae, have a different ecological syndrome; although often trees, they have much smaller seeds and do not show mast fruiting, but like other ECM plants, they can dominate in early successional vegetation, they grow on acidic and peaty soils, and they can tolerate soils with toxic metals (e.g. Read & Perez-Moreno 2003; Nara et al. 2003; Cairney & Meharg 2003). However, as discussed above, the distinction between ECM and ERM fungi is not that great, perhaps especially the ECM associated with Salicaceae, Pinaceae and at least some Quercus (e.g. Villareal et al. 2004 for references); tropical ECM should be examined from this point of view. ECM and their seed-plant associates together form soil conditions that both prefer. In Rhododendron, at least, stable protein-tannin complexes formed by the plant are more easily accessed by its own fungus associates than by fungi from plants with other kinds of mycorrhizal associations (Wurzburger & Hendrick (2009). Similarly, Newbery et al. (1997) found that in some forests on poor soil in Cameroon the phosphorous in soil and litter was preferentially accessed by ectomycorrhizal Dialeae (= Fabaceae-Detarieae) that dominated there, the plants effectively making the kind of soil to suit themselves. Although Näsholm et al. (2013) interpret ECM fungal activities in conifer forests somewhat differently, with nitrogen in some circumstances being retained in the mycelium, the consequences are similar; non-ECM plants will be at a disadvantage in the nitrogen-poor conditions that result. Clemmensen et al. (2013), working on Swedish forests, emphasized that in older, less diturbed forests much carbon came from roots and in particular from their fungal associates. Leaves of ECM plants may decompose more slowly than those of other plants, irrespective of whether they are deciduous or evergreen, and litter from ERM plants may be the most recalcitrant (Cornelissen et al. 2001; Alexander & Lee 2005). The leaves are well defended, often long-lived, and the plants are efficient at removing N and P from them when they die, and the result is persistent, nutrient-poor humus unsuitable for often faster-growing endomycorrhizal plants; in addition, ECM and ERM plants can utilize N as complex organic compounds (Cornelissen et al. 2001. see also above). Whether or not the establishment of conspecific seedlings is less affected than might be expected in such forests needs more study, but in temperate forests the regeneration of the more abundant species (not necessarily ectomycorrhizal) show weaker negative density dependence that that of the less common species (Johnson et al. 2012a, b, c.f. Dickie et al. 2012), perhaps enhancing their dominance, furthermore, in more species-rich areas there is a stronger negative density dependence effect (see also Schnitzer et al. 2011: grasslands; Mangan et al. 2010; Johnson et al. 2012a, b). Overall, in higher latitudes negative density dependence is weakest (Johnson et al. 2012a), and it is at these higher latitudes that ECM species tend to dominate. ECM/ERM communities are often found on rather extreme soils, including serpentines (Branco & Ree 2010), that are either poor in nutrients (e.g. Michelsen et al. 1998), and/or rich in organic materials and/or without much other vegetation. In such communities soil pH is, or becomes, low, and the development of sometimes massive amounts of mor humus is common, especially in cooler climates; podzolization may also occur (van Schöll et al. 2008). Even in the t.l.r.f. of West Malesia there are huge peat lenses on which ECM dipterocarps may dominate (Richards 1996). In general, the acid, nutrient-poor conditions that develop are not conducive to the activity of potential decomposers of humus - a self-reinforcing cycle - and there is CO2 sequestration. Siderophores and organic acids produced by the bacterial associates of ECM fungi and the ECM themselves (Frey-Klett et al. 2007; Taylor et al. 2009) all increase the breakdown of silicate minerals and rock weathering (e.g. Knoll & James 1987). CO2 produced by the respiration of the fungus-plant association is used up in this weathering (Beerling 2005a; Taylor et al. 2008) as it reacts with water CaCO3 and silicate minerals and ultimately carried out to sea (e.g. Berner 1999; Beerling 2005a; Taylor et al. 2009). The low molecular weight organic acids can mobilize cations such as Ca++ and Mg++, increase phosphorous availability, etc.; siderophores chelate iron and oxalate forms complexes with aluminium ions, detoxifying the aluminium but also increasing the weathering of aluminium-containing minerals in rocks (Landeweert et al. 2001; van Schöll et al. 2008). It is not for nothing that ECM fungi have been dubbed "rock-eating fungi" (Jongmans et al. 1997; see also Comas et al. 2012; effect of ECM on rock weathering). There were also increases in the Root Length Density index, an estimate of root length/unit soil volume - wchich would be dramatically changed if the mycorrhizal hyphae were factored in - all in all, foraging for nutrients became more efficient (Comas et al. 2012). Thus the importance of ECM fungi for angiosperm evolution is not just because they facilitate the nutrient and water supply of their associates and make life difficult for non-ECM plants, but also because of their direct and indirect effects on the soil, on weathering, on carbon sequestration, and hence on the earth's climate. ECM plants increase mineral weathering, and rainfall, in part from transpiration, also allows more silicate weathering, and this is a principal sink for atmospheric carbon dioxide (Boyce et al. 2010; Berner, 1999); an increase in atmospheric CO2 removed by the weathering of rock has been linked to the decrease in atmospheric CO2 concentration during the Tertiary (Pagani et al. 2009; Taylor et al. 2009). In drier years, there may even be competition between ectomycorrhizal and lignin-decomposing fungi for water, leading to a reduction in the rate of wood decomposition (Koide & Wu 2003). Finally, carbon in non-decomposing biomass may become buried in sediments. All these biogeochemical effects of ectomycorrhizal plants are as much caused by the activity of fungi and bacteria associated with the plant as by any activities of the plant itself (e.g. Landeweert et al. 2001; Taylor et al 2009; Bonfante & Anca 2009). So answering the questions, "how many times did ECM associations develop, and when did they become common?", is important (see also Eastwood et al. 2011). ECM associations have formed perhaps some 35 times in angiosperms, and over 40 families are involved (Bruns & Schefferson 2004, Wang & Qiu 2006; Smith & Read 2008); associations are particularly common in rosids and in members of the N-fixing clade in particular, but, as mentioned above, ECM dominate in a few clades. Estimates of the age of Fagales, in which ECM-formation may be an apomorphy, are a little more than 100 m.y. (e.g. Cook & Crisp 2005; Friis et al. 2006a; Wang et al. 2009; Magallón & Castillo 2009). On the other hand, Pinaceae, also commonly ECM, may be some 200-350 m.y. old (see Eckert & Hall 2006), although the earliest fossil identified as Pinaceae was found in Upper Jurassic deposits ca 150 m.y. old (Rothwell et al. 2012) and some estimates of the age of crown-group Pinaceae are late Cretaceous or even younger (Willyard et al. 2007; Crisp & Cook 2011). Although suggestions that ECM associations in Dipterocarpaceae and Fabaceae-Amherstieae (= Detarieae) developed before the break-up of Gondwana over 130 m.y.a. (Henkel et al. 2002; Moyersoen 2006) may be overly optimistic, there are massive amounts of dipterocarp resin in India in the Early Eocene, some 52-50 m.y.a. (Rust et al. 2010). The basidiomycete clades involved in these associations may be older than the plant clades, the ability to form ECM evolving at least six to eight times (Hibbett et al. 2000; Hibbett & Matheny 2009). In Boletales, at least, ECM associations may have evolved in the ecological context of soils low in nitrogen (and high in organic material) as the result of activities of brown rot fungi, a number of which are also Boletales (and other fungi: Eastwood et al. 2011). More recently, the crown group origins of ten ECM clades of Agaricales were dated, and they were found to be split about equally between the Late Cretaceous and Eocene, which suggests at least some originated at about the same time or rather later than the plant clades on which they are now found (Ryberg & Matheny 2012; see also Bruns et al. 1998; Horton & Bruns 2001). Normapolles-type pollen and macrofossils associated with it have been linked to Fagales (other than Fagaceae and Nothofagaceae). This pollen was abundant and diverse in the Late Cretaceous fossil record in the area from eastern North America to west central Asia (e.g. Friis et al. 2006a, 2010b and references). Elsewhere in the Northern hemisphere Aquilapollenites and Wodehouseia pollen - affinities uncertain - predominated, in tropical Gondwanan areas pollen of Arecaceae was common, while Nothofagites (linked to Nothofagus, also Fagales) pollen is found in southern areas (Nichols & Johnson 2008 for a summary). If the present and past are connected, Normapolles and Nothofagites plants were ectomycorrhizal; if these plants were abundant in the Late Cretaceous, they may have had a transformative effect on the environment. For further details, see Clade Asymmetries below. 9E. C4 Photosynthesis, Grass, and Grasslands. The global distribution of C4 vegetation is ca 18.8 x 106 km2 and that of C3 vegetation, ca 87.4 x 106 km2 (Still et al. 2003: C4 crops factored in). All told C4 photosynthesis accounts for about 23-28% of terrestrial gross primary productivity (35.3 Pg C yr-1, vs 114.7 Pg C yr-1), although the biomass of C4 plants is less than 5% of the global total, 18.6 vs 407.9 Pg C yr-1 (figures from Still et al. 2003: see also Lloyd & Farquhar 1994; Ehleringer et al. 1997; Retallack 2001). Other estimates of total biomass are similar: 15.6 vs 488.5 Pg C (Ito & Oikawa 2004). Most of the difference is in the woody biomass, that of C3 plants being 352.7 PgC and that of C4 plants zero (obviously Caryophyllales not factored in here!); in both cases root and leaf biomass was estimated to be about equal, that of C3 plants being about twice as much as C4 plants, 36.6 vs 18.6 PgC (Still et al. 2003).
C4 photosynthesis is especially common in Poaceae (Sage et al. 2011); about three quarters of the almost 6,000 species of the PACMAD clade of Poaceae alone have C4 photosynthesis. The C4 photosynthesic syndrome has evolved 22-24 times there, and 66-68 times in Angiosperms as a whole (Sage et al. 1999, 2011, 2012; Ludwig 2011b), as in many species of Cyperaceae (ca 1,500 species), Amaranthaceae (ca 500 species) and other core Caryophyllales, Euphorbiaceae (Euphorbia subg. Chamaesyce), etc. (Arakaki et al. 2011; Sage et al. 2012). Origins in monocots and eudicots are roughly contemporaneous, mostly occuring within the last 30 m.y. or so (Christin et al. 2011b, q.v. for a number of dates; Kadereit et al. 2012; c.f. Cowling 2013 for a rather different take on the evolution of C4 photosynthesis - origins perhaps much more ancient). The great expansion of C4 grassland has occurred only within the last 10 m.y., and within the last 2-3 m.y. in particular (e.g. Strömberg & McInerney 2011; McInerney et al. 2011; Sage et al. 2012). Similarly, the extensive and very speciose Brazilian Cerrado savanna vegetation with flammable C4 grasses also developed within the last (10-)5 m.y. (Simon et al. 2009; Simon & Pennington 2012). One estimate of the global extent of grassland, including savanna, is 52.5x106 km2 (Gibson 2009). Root systems in mature grasslands are dense, and the soils are up to 1 m deep with good crumb structure and rich in organic matter (mollisols: Retallack 2001, 2009). The total carbon sequestration in grasslands is greater than that of the forests they replaced, and in particular the proportion of the biomass sequestered in the soil increases. Grassland soils are notably moister than corresponding woodland soils because woodlands have a lower albedo and transpire more, so somewhat paradoxically grasslands support a cooler, drier climate, yet with increased weathering, which consumes carbon (Retallack 2009). Overall, grasslands can be considered a long-term carbon sink so contributing to long-term global cooling (Volk 1989; Retallack 2001); as Retallack (2009: p. 100) noted, "grasslands did not merely adapt to climate change, but were a biological force for global change". In general, erosion from grasslands leads to a loss of organic carbon in sediment that is an order of magnitude larger than the corresponding loss from forests. Nutrients are also rapidly mobilized and ultimately lost in run-off; the lost nutrients support ocean productivity (Volk 1989). See also also below; for more details on the evolution of grasslands, see Poaceae. Although only some 7,500 species, somewhat over 2% of angiosperms, are C4 plants, they account for about 23% of terrestrial gross primary productivity (Lloyd & Farquhar 1994; Ehleringer et al. 1997; Sage et al. 2012). C4 photosynthesis is very efficient, especially in monocots (Braütigam et al. 2008); C4 monocots do better in warmer environments, C4 eudicots also in colder, drier and saline climates. In the rather cold Gobi deserts 15-17% of the species are C4 plants and they contribute 30-90% of the biomass there (Vostokova et al. 1995; Pyankov et al. 2000). Overall, C4 photosynthesis is efficient, highly polyphyletic, and of great importance ecologically, yet at the same time that importance is geologically only rather recent, C4 grasslands at low latitudes finally coming to dominate only 3-2 m.y.a. (Sage et al. 2012 for references). The adoption of fructans as storage polysaccharide in Poaceae-Poöideae, many Asparagales and Asterales, etc., may also be linked with the ability of the plants involved to grow in seasonally dry or frost-prone climates outside the tropics (Hendry 1993; Hendry & Wallace 1993; Vijn & Smeekens 1999).
9F. Other. There are a number of other eco-physiological groups of angiosperms that are also dominated by a few main clades. 1. Succulence of some form, whether of root, stem or leaf, occurs in some 690 genera and 12,500 species (Nyffeler & Eggli 2010b; see also von Willert et al. 1990; Eggli & Nyffeler 2009). Succulents include species which either avoid drought, although they are rarely found in the driest conditions, or are salt tolerant - usually mutually exclusive strategies (Ogburn & Edwards 2010), and include many of the C4 chenopods mentioned above, Cactaceae, Crassulaceae, a number of epiphytes, pethaps particularly orchids, etc. 2. CAM-type photosynthesis is particularly prevalent in clades that either grow in arid terrestrial environments or are epiphytes; succulent epiphytes are quite often CAM-type plants. All told, some 17,000 or more species in Crassulaceae, Bromeliaceae, Cactaceae and Orchidaceae-Epidendroideae in particular have CAM or its variants (Winter & Smith 1996b; Sayed 2001). The origin of CAM clades seems to be largely contemporaneous with that of C4 clades, being largely Miocene and younger, indeed, there seems to have been a "global surge" of succulent CAM plant diversification within the last 10 m.y. like that of C4 grasslands (Edwards & Ogburn 2012: p. 726). 3. Lianes may make up some 25% (10-44%) of both stem density and species richness of woody plants in tropical forests, and they are especially prominent in disturbed forests; stem-twining vines seem to be commoner in old forests, tendril vines in younger forests (Schnitzer & Bongers 2002). Ca 8,700 species of scandent plants are recorded from the New World alone (Gentry 1991). Major clades of lianes include Menispermaceae, Bignoniaceae-Bignonieae, and Sapindaceae-Sapinoidea-Paullinieae. 9G. Summary. We can now return to the issue of when l.t.r.f. as we know it appeared (see above). As with flowers, is not the evolution of angiosperms per se that marks any main changes; these occurred later (Feild & Arens 2007). The venation density of ANITA-grade angiosperms is rather similar to that of non-angiosperm lignophytes and their xylem is in several respects functionally not that different. Early angiosperms may be perhaps distinguished from gymnosperms by their fast seedling growth and overall short reproductive cycles (e.g. Bond 1989; Coiffard et al. 2006). but, as Feild and Arens (2007: 21) noted, "Among basal angiosperms, the initial transitions to higher-light environments are characterized by a high degree of lineage-dependent, functional experimentation, in which fine-tuned performances were assembled piece-by-piece." Venation density showed two marked increases in the Cretaceous, one around the Middle to Late Albian ca 106-100 m.y.a., early in the Cretaceous Terrestrial Revolution, and one around the K/T boundary, when values reached 12-16 mm mm-2 (Feild et al. 2011b). Large trees first appear in the fossil record in the Middle to Late Albian, and wood with scalariform perforation plates was particularly common in the Cretaceous (Wheeler & Baas 1993). Features like vessel length and perforation plate morphology - scalariform perforation plates became less common - that would favour xylem conductance, and wood parenchyma, but not ray morphology, changed across the K/T boundary (Wheeler & Baas 1991). Such changes may be connected with changes in venation density and water conductance needs, but, as Wheeler and Baas (1993) noted, there is conflict between features of Cretaceous fossil woods and paleoclimatic indicators, indicators that are based on our understanding of how wood of extant plants functions (see also Philippe et al. 2008). Increased plant productivity and diversity would also allow animals that ate, pollinated or dispersed angiosperms to diversify (see also Boyce et al. 2010). Light conditions in the closed forest habitat pose a particular challenge. The PHYA/C gene pair duplicated before the origin of crown group angiosperms, and PHYA in particular may have been very important in angiosoperm evolution. PHYA is intimately involved in germination and in etiolation responses of the seedling, especially in shady conditions such as occur on the forest floor, for example, preventing seedling etiolation is response the the far-red light that dominates the spectrum there. Furthermore, it is involved in the germination response of hydrated seeds to very brief pulses of light (the very low fluence response - VLFR) such as sunflecks or in disturbed conditions (Mathews et al. 2003). Unfortunately, how ANITA grade angiosperms might resopond to manipulation of their PHY genes is unknown. When thinking of overall patterns of seed plant diversity and evolution, there are a number of striking examples of what may be called clade asymmetries. There are two rather different kinds of these asymmetries. One includes small (in terms of species numbers) clades of pollinators and seed dispersers that are of particular importance for whole communities or ecosystems. These are quite well known, especially on a fairly local scale (e.g. Johnson 2010). The other includes asymmetries in more physiological-ecological relationships, where relatively small clades of seed plants have a major effect on biome functioning. Both kinds of asymmetries have major implications for species persistence, the ecological structuring of communities, and the way one thinks about diversity. Specifically, we now have the tools to identify and think about the great ecological impact of a few and not notably speciose clades of plants and animals that are either restricted to particular biomes or provide comparable services across biomes (see below for keystone clades and ecosystem engineers). There is the general issue of the relation between diversity and community/ecosystem stability. Thus Petchey and Gaston (2002a, b) suggested that if functional diversity/functional traits in the community were to be conserved, a large proportion of species in that community would also have to be preserved; there was little redundancy in functional diversity. It is easy to ask questions like "How many species of plants are dispersed by a particular group of bats?", and "How many species are pollinated by a particular group of bees?". However, it is very difficult to obtain reliable answers. Estimates of the numbers of species of bees or bats may be fairly accurate, but the same cannot be said of the numbers of species of plants that they service. Many observations in the literature do not allow one to distinguish between a visit of an animal to a plant that is casual or one that is indicative of a close relationship between the two, even aside from the fact that such relationships may change over the season or between seasons (e.g. Ollerton et al. 2003 and references), but, worse, there is an absolute dearth of observations. As Ollerton et al. (2011: p. 321) note, "if a policy-maker or conservation planner were to ask an ecologist the straightforward question, 'How many species of flowering plants are pollinated by animals?' the answer would be: 'We do not know'." In any one community there may be up to 50 species of bees (Roubik & Hanson 2004; Zimmermann et al. 2009); Hentrich recorded ca 23 species of bees visiting ca 48 species of plants in Nouragues, French Guiana. It is estimated that crown group euglossine diversification occurred only 42-27 m.y.a., montane clades diverging only in the last 8-4 m.y. (Ramírez et al. 2010); another estimate of crown group age is (35-)28(-21) m.y.a. (Cardinal & Danforth 2011). Local diversity of bumble bees can be quite high, and one fifth or more of the world's bumblebee species are found in the Sichuan-Chongqing region of China (Williams et al. 2009). Bumble bees seem to have diversified over a similar time frame as did the euglossine bees, i.e. about 40-25 m.y.a. The Eocene-Oligocene boundary of ca 34 m.y.a. was a time of sharp cooling and increase of seasonality, and bumble bees flourish in cooler climates, being facultatively endothermic (Hines 2008 and references). Cardinal and Danforth (2011) suggest a somewhat more recent age for crown-group bumble bees of (31-)21(-12) m.y. The bees moved into South America about 8-6 m.y.a., perhaps along with the plant genera of northern origin that they pollinate (Asmussen & Liston 1998; Hines 2008). The age of crown-group honey bees is estimated at (30-)22(-16) m.y. (Cardinal & Danforth 2011). The evolution of flowers which have oils as their primary reward may have begun in the Eocene (Renner & Schaefer 2010). However, Cardinal and Danforth (2013) estimated that Centradini and Tetrapedia, which take oil from Malpighiaceae, evolved in the Late Cretaceous (87-52 and 92-66 m.y.a. respectively); see also Neff and Simpson (1981) for the bees. In the Andes, the trap-lining hermits, sister to other humming birds (Bleiwiss 1998a), tend to be commoner at lower altitudes, while several clades have independently moved into high altitude habitats (Bleiwiss 1998b; McGuire et al. 2007 and references). Traplining birds may visit fewer species of plants than do territorial birds (Snow & Snow 1980). Local diversity of humming birds can be high, with 25-30 species in a single assemblage (Graham et al. 2012); figures in Fleming et al. (2005) are 3-28 species per site, pollinating 14-51 species of flowers from herbs (commonest), whether epiphytic or not, to trees. Of course, many humming birds eat insects and they also visit quite a variety of flowers usually pollinated by other animals, while animals other than birds may pollinate flowers visited by humming birds (e.g. Snow & Snow 1980; Fleming et al. 2005). Humming birds and swifts probably diverged in the Palaeoecene ca 57 m.y.a. (Bleiweiss 1998a), and rather surprisingly, the earliest humming birds known are from Oligocene Europe in deposits ca 30 m.y. old (Mayr 2004). Crown-group humming bird diversification seems to have begun much later in lowland South America, speciation occurring about 13-12 m.y.a. along with the uplift of the Andes (Bleiweiss 1998a; McGuire et al. 2007). To integrate: About 590 New World species of plants in 180 genera are pollinated by phyllostomid bats, over three times the number of bat-pollinated flowers in the Old World (Dobat & Peikert-Holle 1985); most bat-pollinated plants are often more or less woody or epiphytic (Fleming et al. 2005). In any one site there may be 1-6 species of bats, and these pollinate 4-19 species of flowering plants (Fleming et al. 2005). Only 39 species of bats are involved, and nectarivory has evolved twice; diversification has occured within the last 30 m.y. (Datzmann et al. 2010). Major diversification of fruit-eating phyllostomid bats began (27-)22(-18) m.y.a. in the late Oligocene to mid-Miocene (Datzmann et al. 2010; see also Rojas et al. 2011). This is a long time after the beginning of diversification of Piper, at least, raising the question of how what now seems to be close to an obligate relationship of both sides has evolved (Fleming 2004). Both humming birds and phyllostomid bats, restricted to the New World, are more specialized than their Old World ecological counterparts (African sunbirds show a moderate degree of specialization). Similarly, bird-pollinated flowers, at least, in the New World also seem to be more specialized (Fleming & Muchhala 2008). Humming birds tend to pollinate herbs and epiphytic plants, while in the Old World nectar-eating birds more frequently pollinate larger trees (Stiles 1981; Fleming & Muchhala 2008). Discussion.
Asymmetries in pollinator and fruit dispersal relationships have important implications. Small groups of animals, "generalists" from one point of view, all service a disproportionately large number of plants, and we think of the plants involved as "specialists" (for pollination/dispersal syndromes and guilds, see also characters). Considerable work has been done of pollinator-plant relationships in southern Africa, and there very specialized pollination systems, pollination guilds, have been documented for a variety of pollinators; some 20-30 species of plants, often belonging to quite unrelated families, depend on the services of one species or a small group of pollinators (Johnson 2010). It may be noted that oligolectic bees, bees that visit relatively few flowers, were initially categorized as such based largely on observations on plants visited for pollen, but pollination also occurs when bees are nectaring; add variation in time and space, and characterizing pollination relationships becomes difficult (e.g. Waser et al. 1996). Oligolecty has often been thought of in terms of how many families of plants a bee species visits; it may visit several genera and species within that family (e.g. Waser 1996). Although members of a polylectic bee, or even an individual bee, may visit many species of plants, on any one trip the bee is likely to be much more selective (e.g. Heard 1999; Hagbery & Nieh 2012 for general pollen/nectar constancy), visiting only one or a few species, so being functionally mono- or oligolectic. Several apparent paradoxes are evident. For instance, the morphology of a polylectic pollinator is not necessarily generalized, thus polylectic bees such as Apidae have a well developed sensory system, etc., and the southwest African nemestrinid fly Moegistorhynchus longirostris has a tongue 40-90 mm long (Johnson 2010). Individual interactions of such pollinators may be exquisitely precise, witness the deposition of pollinaria by Catasetum on a visiting euglossine bee by an orchid, and the complex morphologies of the male and female flowers of the orchid (for which, see e.g. Darwin 1862a). Oligolectic bees, on the other hand, may lack specialized morphological adaptations for pollination (Michez et al. 2012). Specialized monosymmetric flowers are usually visited by one or a few species of polylectic pollinators, be they bees (several species of bess visiting one species of Pedicularis - Macior 1982), flies, or humming birds, although a single species of pollinator may visit over a hundred species of flowers; pollination efficacy in such flowers may even be less than that in generalized flowers (Ramirez 2003). Plants with generalist-type flowers are visited more by oligolectic pollinators, and a single species of plant may be visited by several species of oligolectic bees. Thus in arid and semi-arid areas (California, Chile) there are many species of bee, and specialist/oligolectic bees are common and compete for the same resource (see in part Moldenke 1976, 1979a, b; Petanidou & Ellis 1996; Lindberg & Olesen 2001; Stang et al. 2007). Of course, oligolectic bees may also pollinate monosymmetric flowers (e.g. Sedivy et al. 2008) and polylectic bees monosymmetric flowers (Sedivy et al. 2013). Monosymmetric flowers in which precise interactions between plant and pollinator are needed for effective pollination have become more common over evolutionary time, yet simultaneously bees, for example, have increasingly tended to pollinate a greater variety of hosts; polylectic behaviour in bees is often derived (e.g. Müller 1996; Michener 2007; Sedivy et al. 2008; Litman et al. 2011; Danforth et al. 2013; c.f. Moldenke 1979b). It is less that long-tongued euglossine bees pollinating a variety of Zingiberales have specialized on flowers with long tubes, but rather, long-tubed flowers have specialized on long-tongued pollinators (Borrell 2005; see also Johnson 2010). Overall, species of plants with specialized flowers predominate, as do species of bees that visit a relatively few species of plants. The two groups interact relatively little, and pollinator-plant relationships are not nested in any simple fashion; specialists interact with generalists and generalists interact with both specialists and generalists (e.g. James et al. 2012; c.f. Bascompte et al. 2003). Similarly, fruit eating phyllostomid bats that are ecologically specialised may be generalists when looking and bat/plant networks (Mello et al. 2011a). Even in extant communities ecological relationships between species are by no means constant (e.g. Aizen et al. 2012). The asynchrony in timing of the evolution of the two partners in pollination relationships that may now seem to represent an obligate association for at least one of the two (e.g. Fleming 2004; Ramirez et al. 2011; Schiestl & Dötterl 2012) also suggests the fluidity of such relationships. Indeed, many of the asymmetric relationships mentioned above are of relatively recent origin. When thinking about such asymmetric relationships the idea of pollinators being some sort of keystone species and showing phylogenetic niche conservatism (e.g. Fleming et al. 2005; Johnson 2010) readily spring to mind. For a polylectic pollinator that serves as a hub (when diagramming out plant-pollinator relationships) the effect of the extinction of a single species of plant may be slight, but the extinction of such a pollinator may affect some of the plants it pollinates more seriously - of course depending on the overall patterns of modularity and connectedness of the plant-animal relationships (see Waser et al. 1996; Lindberg & Olesen 2001; Rezende et al. 2007; Stang et al. 2007; Olesen at al. 2007; Vamosi & Vamosi 2012; also Vásquez & Simberloff 2002: disturbance and pollination; Colles et al. 2009; Armbruster 2012). For oligolectic pollinators, the relationship may tend in the reverse direction, while specialists or species with low frequencies of interactions are more likely to go extinct than species with more diverse sets of interactions (Aizen et al. 2012; James et al 2012). New World phyllostomid fruit bats have networks that are more highly nested and have higher connectance than fruit:bird networks, but were less robust to extinctions, perhaps because of the monophyletic origin of fruit bats and the polyphyletic orgin of fruit-eating birds; at the same time, there was low complementary specialization within a network (Mello et al. 2011a, b). [elaborate or delete: Rezende et al. (2007) suggested that extinctions might have some phylogenetic signal, but this is certainly not always true (Ramírez et al. 2011).] Bengtsson (1998) and others have emphasized that species numbers are only one metric of evolutionary importance or success, however, numbers are quite easy to come by so they are usually the metric of choice. Estimates of biomass, productivity, even area occupied, whether for clades or for species, are much harder to obtain, but are other metrics to use, and from the point of view of global ecosystem functioning are of great importance. Here the focus is on particular clades of seed plants, sometimes quite small in size, that have a disproportionately large effect on communities, ecosystems, even the global environment. They dominate the communities in which they occur and fix and/or sequester large amounts of carbon. Of course, in almost any community there are common species; one can almost expect 25% of the species to contribute 50% of the biomass or over 80% of the individuals (Gaston 2011: the slope of biomass accumulation is less than that of species accumulation; Gaston 2010; e.g. M. D. Smith & Knapp 2003), but the asymmetries discussed below are more extreme. Although Pitman et al. (2001) found a surprisingly large number of common (>1 individual/ha) and widespread species in the terra firme forests of western Amazonia, these species are not common by the standards adopted here, interestingly, none of the 42 species they mentioned is known to be ectomycorrhizal, a group that figures largely in the discussion below. Furthermore, species that are dominant only in early successional phases (Type II transitional dominance: Connell & Lowman 1989) are not considered here. Indeed, a complicating factor is the extent to which some of the vegetation types discussed here reflect human activities (see below), indeed, the impact of human activities may affect biomass estimates (Dixon et al. 1994). Although estimates of biomass, primary productivity, etc., are given below, they should be taken with more than a grain of salt. Estimates can vary very widely (e.g. Brown & Lugo 1984; Botkin & Simpson 1990; Dixon et al. 1994; Chmura 2011). Not only do different countries have different definitions of "woodland", "grassland", "peat soils", and the like, but the distinction between communities such as sea-grass, marine salt-marsh and mangrove communities are not always clear. It is also easy to forget that there are three different kinds of tons, and which is being used is not always mentioned. Ideally, biomass estimates for both above and below ground are needed, but frequently estimates of only one are given. 2A. C4 photosynthesis, grass, and grasslands together make up a major component of global ecology. Overall only somewhat over 2% of angiosperms - perhaps some 7,500 species - are C4 plants (Sage et al. 2012). They can be divided into three main groups: grasses, sedges, about which little is known ecologically, and core eudicots, particularly chenopods, although in none is the origin of C4 photosynthesis monophyletic. For an entry into the literature, see Sage et al. (2012); drivers of the evolution of this distinctive syndrome are probably the decrease of CO2 in the atmosphere at the beginning and again towards the end of the Oligocene, and increasing temperature, which together would lead to an increase in photorespiration, perhaps the immediate driver in the evolution of the syndrome - but it will be clear that we understand little about details of the origin and spread of the syndrome (see also Cowling 2013). The global distribution of C4 vegetation is ca 18.8 x 106 km2 and that of C3 vegetation, ca 87.4 x 106 km2 (Still et al. 2003, q.v. for map). All told C4 photosynthesis accounts for about 23-28% of terrestrial gross primary productivity (35.3 Pg C yr-1, vs 114.7 Pg C yr-1), although the biomass of C4 plants is less than 5% of the global total, 18.6 vs 407.9 Pg C yr-1 (figures from Still et al. 2003: see also Lloyd & Farquhar 1994; Ehleringer et al. 1997; Retallack 2001). Most of the difference is in the woody biomass, that of C3 plants being 352.7 PgC and that of C4 plants zero (obviously Caryophyllales not factored in); in both cases root and leaf biomass was estimated to be about equal, that of C3 plants being about twice as much as C4 plants, 36.6 vs 18.6 PgC (Still et al. 2003). Other estimates of total biomass are similar: 15.6 vs 488.5 Pg C (Ito & Oikawa 2004). The great expansion of C4 grassland began in the Miocene a mere nine m.y.a. and was completed only 3-2 m.y.a. (e.g. Strömberg & McInerney 2011; McInerney et al. 2011 for North America); for further details, see Poaceae. Grass-rich savannas like the Cerrado in South America developed at about the same time (Simon et al. 2007; Simon & Pennington 2012; map: blue green, more or less pure grassland, olive green, communities with trees and shrubs as well as substantial grass, see endpapers in Coupland 1993a, b; esp. White et al. 2000, Map 1, for details). For good summaries of the ecology of grasses and grasslands, see Coupland (1993a, b), White et al. (2000) and Gibson (2009). The balance of evidence suggests that fire, increased temperature and low CO2 all interacted in the spread of C4 grasses, grasslands and savanna, C4 photosynthesis minimizing photorespiration and grasses being particularly flammable because of the litter they produce (Scheiter et al. 2012; Sage et al. 2012). Although there are some 11,300 species of grasses, only some 600 species dominate ecologically worldwide, and most of these are C4 photosynthesizers (Edwards et al. 2010). Productivity estimates for grasslands in particular, including both C3 and C4 species - are that they currently account for 11-19% of net primary productivity on land and 10-30% of soil C storage (Hall et al. 2000); Gibson (2009) suggests that grasslands store 650-810 GtC, ca 33% of the global total, and 55-95% of that is stored underground, the higher values being in higher-latitude (probably = Arctic) areas. Grasses also have a great effect on soils and weathering (see above). Grassland grasses have dense root systems, and savanna trees allocate relatively more carbon to below-ground biomass than do forest trees (Scheiter et al. 2012). Chenopods. C4 eudicots are often found in some combination of arid, ephemeral, warm to cold (at least in the winter), disturbed and/or saline conditions (Ehleringer et al. 1997; Kadereit et al. 2012). In the rather cold Gobi deserts of Mongolia 15-17% of the species are C4 plants, and over 50% of these are chenopods; chenopods contribute 30-90% of the biomass there. Overall C4 plants are only 3.5% of the total Mongolian flora (Vostokova et al. 1995; Pyankov et al. 2000). In such areas in general Amaranthaceae-Chenopodioideae are over half the C4 species (Pyankov et al. 2000). Similar fast-growing C4 Chenopodioideae (and some Polygonaceae), some of which are arborescent (Haloxylon aphyllum can attain 10 m in height with a trunk 1 m across: Winter 1981), also dominate the halophytic vegetation of the somewhat warmer Central Asian Turanian deserts (Winter 1981). Succulent C3 chenopods are common in the Gobi in true desert conditions, and also in moist, saline soils (Pyankov et al. 2000). Aridification in Australia began early in the Miocene ca 22 m.y.a., and Amaranthaceae-Camphorosmeae (145 of 147 species) radiated there ca 7.5 m.y.a. (Cabrera et al. 2012). C4 taxa like Atriplex also diversified in Australia; the genus was probably a major item in the food of the extinct giant (ca 230 kg) kangaroo Procoptodon goliah (Prideaux et al. 2009; Kadereit et al. 2010). The almost 4,000 species of Ericaceae with ericoid mycorrhizae (ERM) are not included in the totals above. However, Vrålstad (2004) and others have suggested that ECM and ERM form a single ecological guild, one of whose characteristics is being intermediaries in the uptake of organic nitrogen by the plant, and they are included in the discussion below. Orchid mycorrhizae, with ERM often considered to be modified ECM, are not discussed here. ECM/EM plants are especially common in (cool) temperate/montane habitats, but also in West Malesian dipterocarp forests, Australian Eucalyptus woodland (about which little seems to be known) and African Miombo, Mopane, and Sudanian woodlands, and considerable areas of the Guineo-Congolian coastal and Ituri rainforests (e.g. Hart et al. 1989; Malloch et al. 1980; White 1983; Safer 1987; Hart et al. 1989; Sanford & Cuevas 1996); Sudanian and Miombo woodlands are biogeographically close (Linder et al. 2012). A very approximate estimate of the number of these dominant species is 1,000. This includes ca 160/388 species of Dipterocarpaceae, 11/13 Nothofagaceae, and 50/165 Fagaceae from Malesia alone (data from Ashton 1981; Soepadmo 1972), however, Ashton (pers. comm. vii.2012) noted that only ca 13 species were major dominants. Ca 20 species of Ericaceae are widespread in boreal forest and tundra habitats, although a number of species of Vaccinium can be very abundant locally in montane forests in Malesia and of Rhododendron in the Himalayas-Yunnan region. Many vegetation types dominated by an ECM species also include a variety of other ECM/ERM plants. Thus in the Mediterranean Maquis, ECM Cistaceae, Fagaceae and Pinaceae are all important components of the vegetation. There are extensive oak-pine ECM forests in the eastern United States, Mexico, and the Mediterranean, forests with ECM Fabaceae, Dipterocarpaceae and Phyllanthaceae are common in tropical Africa, while the understory of boreal forests, dominated by ECM Pinaceae, often includes a notable element of ERM Ericaceae. In western North America the oak-pine forests have a substantial amount of Arbutus menziesii (Waddell & Barrett 2005), an ericaceous tree with arbutoid mycorrhizae. But ECM plants do not simply dominate communities, many are large individuals, each one representing a considerable amount of standing biomass, and large amounts of carbon often accumulate (see also above). Dipterocarps largely dominate Southeast Asian tropical peatlands (most are Malesian, and in particular Indonesian). It has been estimated that Dipterocarpaceae occupy about 3/5 of the total tropical peatland area, close to 250,000 km2, and about 6.2% of the global peatland area (Page et al. 2011). This peat contains about 68.5 Gt carbon, a figure that is some 77% of the tropical and 11-14% of the global totals for peatlands; note that these figures do not include estimates of above-ground biomass (Page et al. 2011). Dipterocarpaceae also grow away from peatlands, but often on rather humus-rich soil, as in Lambir forest, Sarawak. There they make up only 7.4% of the species but 41.6% of the basal area (918.41 m2); the figures for Shorea alone are 4.7%, 21%, and 467.8 m2, Dryobalanops aromatica and Dipterocarpus globosus between them accounted for 13.2% of the basal area, and seven dipterocarps (out of the ten most dominant species) accounted for 23.1% (Davies et al. 2005). Carbon in waters draining from disturbed dipterocarp peat swamps may be as much as ca 4,180 years old (Moore et al. 2013), indicating that carbon storage here can be quite long term. Shorea robusta (sal) is a gregarious tree that grows in monsoon areas from Pakistan to China, especially in the India-Assam-Myanmar area. Sal forests occupy 115,000 to 120,000 km2 (11.5x106 ha) and make up ca 15% of Indian forests (Tewari 1995). In Africa Monotes is a significant component of the rather dry forests and woodland dominated by Fabaceae-Detarieae (see below). Pinaceae are the major component of boreal forests. Estimates of the area occupied by these forests range from 12x106 km2, or ca 17% of the land surface of the earth (Moore 1996; Lindahl et al. 2002), to only 9.2x106 km2, a figure that is 73% of the conifer forests of the world (Kuusela 1992). ECM Pinaceae, along with some Salicaceae and Betulaceae, also ECM, make up the bulk of these forests, while ERM Ericaceae often dominate in the understory (e.g. Villareal et al. 2004; Vrålstad et al. 2002; Vrålstad 2004; Kranabetter & MacKenzie 2010). Botkin and Simpson (1990) estimated above-ground biomass and carbon for boreal forests in North America to be 4.2±1.0 kg/m2 and 1.9±0.4 kg/m2 respectively which, when extrapolated to a total forest area of 5,172,427 km2 gave total biomass and carbon figures of 22.5±5x1015 g and 9.7±2x1015 g respectively. Moore (1996) estimated living above-ground biomass ("phytomass") in North American boreal forests as 12x1015 g, to which could be added 76x1015 g in soils (including dead and fallen trees) and 135x1015 g in peatlands. Extrapolating to a total area of 12x106 km2, this would then give estimates of . suggested that the core area of boreal forests in Eurasia alone to be 12x106 km2, so perhaps the global total is as much as 17.1x106 km2... Carbon burial figures are estimated at 49.3 Tg C y-1 (Chmura et al. 2011: area 13.7x106 km2). Estimates of the current carbon pool for forests in Russia, Canada, and Alaska, roughly boreal forest, are 88x1015 g (vegetation) plus 471x1015 g (soils), the area under forest cover being 13.7x106 km2 (Dixon et al. 1994). Fabaceae are not generally thought of as being ECM plants, but a number of trees, especially members of the Old World Detarieae, have been reported as being mycorrhizal (e.g. Onguene & Kuyper 2001). Some 36 of the ca 82 genera included in Detarieae are reported as being at least locally dominant (e.g. Letouzey 1968; Mackinder 2005), and 11 of these dominants are in a rather small clade (Macrolobieae/the Berlinia clade) with 16 genera, of which 10 are known to be ECM (see also Wieringa & Gervais 2003). Some Detarieae like Cynometra are endomycorrhizal (but this can also be a dominant tree: Eggeling 1947; Makan et al. 2011), while a few other Fabaceae, both ECM and VAM, may also dominate locally. A few species of Fabaceae-Detarieae dominate ca 3.316-3.8 x 106 km2 of Miombo and Mopane forests in the Zambezian region (estimates from White 1983; see also Newbery et al. 2006). In Miombo forests Detarieae represent 20-90% of the trees, 30-96% of the basal area, and with biomass estimates in the range of 35-97 Mg ha-1 (Frost 1996). [More figures waiting to be added.] Isoberlinia is a major component of Sudanian Woodland (White 1983) which forms an interrupted band south of the Sahara from Mali to Uganda (White 1983; upper band of blue in the map above). This forest is biogeographically closest to Miombo woodlands among other African vegetation (Linder et al. 2012). Detarieae are ecologically important elsewhere in Africa. Gilbertiodendron dominates large areas of the eastern Congo Ituri rainforest (Makana et al. 2011). Microberlinia dominates Guineo-Congolian forests in Cameroon, and other Detarieae dominate parts of the coastal forest from Sierra Leone to western Gabon, and again in the periphery of the Zaire basin (White 1983). Indeed, a caesalpinioid Biafran forest subtype has been recognised, and of the 34 important genera recorded from this forest, 28 are Detarieae, and 11 of these are described as being characteristically gregarious (Letouzey 1968). Fagaceae, Nothofagaceae, and many other Fagales are common in forests in the eastern and western parts of Eurasia and North America, and also in the southern temperate regions. They often grow in association with ECM Pinaceae, as in eastern north America (e.g. Abrams 1996). The American chestnut, Castanea dentata, was previously the dominant tree in some 800,000 km2 of forest in eastern North America; although it now persists largely as suckers after its devastation by chestnut blight in the first half of last century (Thompson 2012), it has been largely replaed by other ectomycorrhizal trees (Abrams 1996). Oak trunks may get buried in sediment in flood plains, and the mean age of carbon storage in such conditions is ca 1,960 years, individual trunks being up to 14,000 years old (Guyette et al. 2008). Ericaceae are important components of tundra vegetation, which occupies 8% of the global land surface (Kranabetter & MacKenzie 2010; Gardes & Dahlberg 1996). Such habitats are dominated by "ericoid" plants, Ericaceae, but also Diapensiaceae (e.g. Bliss 1979). The mycorrhizal status of Diapensiaceae needs clarification, and although belonging to Ericales, the family is not immediately related to Ericaceae, however, only one species, Diapensia lapponica, with a circumpolar distribution (see Diapensiaceae, is involved. All other ericoid plants in these habitats are Ericaceae, Vaccinium and Empetrum being two of the dominant biomass accumulators (Kranabetter & MacKenzie 2010; Gardes & Dahlberg 1996). Ericoid plants represent 30-87% of the above-ground biomass and 40-83% of the net annual above ground primary productivity in tundra (figures from Bliss 1979), and ECM and ERM plants together made up more than 95% of the vascular plant biomass in some heath tundra sites (Michelsen et al. 1998). In this context, another area on which to focus is the permafrost region. The northern polar permafrost encompasses the tundra region and also much of the boreal conifer forest above 60o N, if areas of patchy permafrost are included, although only above 70o N in western Asia and even further north in much of Europe. The map here is based on that by Brown et al. (1997, q.v. for detail; c.f. Tarnocai et al. 2009); areas with some, but less than 50%, permafrost are extensive, but are not included. Tarnocai et al. (2009) estimated permafrost to occupy about 18 x 106 km2, about 16% of the global soil area. The total amount of organic carbon in the permafrost area, which includes both extensive bogs dominated by Sphagnum and Cyperaceae as well as deltaic deposits, is estimated to be 1672 Pg, about 50% of the global below-ground organic carbon pool, and of this, 88% is in permanently frozen soils (Tarnocai et al. 2009: estimates of carbon in peatlands are broken out separately). Much of this carbon is stored below 200 cm (Tarnocai et al. 2009). The following three communities, sea-grasses, mangroves and tidal salt marshes, all have carbon burial rates well over 100 g C M2 y-1, which is considerably more than twenty times that in tropical, boreal or temperate forests (usually substantially less than 10 g C M2 y-1: Mcleod et al. 2011; Chmura 2011). All three systems are accretionary, in that they also capture much sediment in which the carbon they produce, but also allochthonous carbon, is stored, the deposits reaching 10 m or more thick (Chapman 1974; McKee et al. 2007; Mcleod et al. 2011; Chmura 2011; Fourqueran et al. 2012); storage may be for thousands of years, well over ten times as long as that in tropical rainforest, for example (Chambers et al. 2001; Mcleod et al. 2011). The divergence of the two main sea-grass clades, one including Hydrocharitaceae and the other Posidoniacaeae, etc., is dated at ca 107 m.y.a., while within the latter group the first split can be dated to ca 73 m.y. (Janssen & Bremer 2004). The sea-grass ecosystem is of great ecological importance: In brief, it is very productive, supports a considerable amount of diversity, does not suffer from much herbivory, captures much sediment, and stores much carbon, both autochthonous and allochthonous (Orth et al. 2006; Kennedy et al. 2010 for summaries). Sea-grasses often form monodominant stands, individual clones of some species being very long-lived. The gross primary productivity of sea-grasses has been estimated at 1903 g C m2y-1, rather like that of mangroves, their global primary productivity is 628 Tg C y-1, while their net ecosystem production (1211 g C m2 y-1 and globally 400 TgCy-1) is substantially higher than that of mangroves because of their relatively low respiration rates. Sea-grasses are responsible for 1.13% of all marine primary productivity, yet they bury as much as an estimated 27-44 Tg C y-1, some 12% of the total C storage in the marine ecosystem (Duarte et al. 2005: area 30x106 ha; Duarte 2011) - this while occupying less than 0.2% of the area of the oceans, and it has recently been suggested that this burial estimate may be only one half the actual amount (Fourqueran et al. 2012). Although the ammout of carbon in the sea-grass plant itself is small, that stored in the soil, which can form mats up to 11 m thick in the Mediterranean, is very great (Fourqueran et al. 2012), larger than that of most forests and comparable with mangrove storage. Indeed, sea grasses trap not only sediment but allochthonous carbon, too, and when thinking about sea-grass communities as carbon sinks, then an estimate of 169-186 g C m-2 yr-1 seems reasonable - net community production of ca 120 g plus 41-66 g of allochthonous C (Kennedy et al. 2010: highest areal estimate below). Importantly, estimates of areas occupied by sea-grass communities range from 22.8x106 (Waycott et al. 2009) to 30 x 106 (Duarte et al. 2005) to 60 x 106 ha (); although the last is an old estimate, it is relevant here where the emphasis is on conditions immediately before human activities became transformative. A substantial amount of sea-grass carbon moves into other marine ecosystems, including the deep sea (Suchanek et al. 1985). Not surprisingly, estimates in Mcleod et al. (2011) vary - they suggest a carbon burial rate of (100-)138(-176) g C m-2 y-1 (range 45-190), total carbon burial of 48-112 Tg C y-1), for a sea-grass area of 17.7-60.0x106 ha). Other estimates of global carbon storage by sea-grasses range from 4.2-8.4 or 9.8-19.8 Pg C, depending on the assumptions made, which is somewhat over 0.5% the global total (Fourqueran et al. 2012; see Charpy-Roubaud & Soumia 1990 for estimates of benthic algal productivity). This carbon may be sequestered for 4,000 years or more in the anoxic soils of sea-grass beds (Orem et al. 1999; Serrano et al. 2011, 2013). By the Eocene, ca 50 m.y.a., many mangrove genera are known from the fossil record, and several, including Pelliciera, are known from both the Old and the New World (but see Martínez-Millán 2010). Pelliciera is now Central American, although growing in Europe in the past (Plaziat et al. 2001; Ricklefs et al. 2006 for some dates). Nypa, today found only in the Indo-Malesian area, appeared in the Upper Cretaceous ca 70 m.y.a. and by the early Palaeocene ca 55 m.y.a. was found in both the Old and New Worlds (Arecaceae, q.v. for fossils). There are fossil hypocotyls identified as Ceriops and preserved with good anatomical detail in the Lower Eocene London Clay (Wilkinson 1981; but c.f. Collinson & van Bergen 2004). Rhizophora is known from the Caribbean in the late Eocene (Graham 2006) and Rhizophoreae from the Early Eocene 55-48.5 m.y.a. in western Tasmania, Australia (Pole 2007). The mangrove ecosystem is very productive and also has high carbon flux rates. Mangroves occupy 13.7-15.2 million hectares, and they store 4-20 PgC globally (Bouillon et al. 2008; Donato et al. 2011 and references; 16.7 m ha in Valiela et al. 2001), although towards the beginning of the last century there may have been 22.0-25.5x106 hectares (figures estimated from Valiela et al 2001, correction of current figures by change in those multiyear records that exist, also with the lower current estimate of Spalding et al. 2010). Other estimates are that they bury 17.0-23.6 TgC y-1, their gross primary productivity is 2087 gCm2y-1, global primary productivity is 417 TgC y-1, but with a rather lower net ecosystem production (221 gC m2 y-1 and globally 44 TgC y-1) because of a relatively high respiration rate, at least when compared with the sea grass community (Duarte et al. 2005: area 0.2 x 1012 m2). Spalding et al. (2010) estimated net primary productivity to be 140-168 tg y-1, of which 10(-30)% was incorporated into sediments, which makes up 15% of the organic carbon accumulating in marine sediments globally. 10% of refractory organic carbon in marine sediments may come from mangroves, which equals the amount of carbon in atmospheric CO2 (Spalding et al. 2010). Estimates in Mcleod et al. (2011) are a carbon burial rate of (187-)226(-265) g C m-2 y-1 (range 20-949), total carbon burial of 25.7-40.3 Tg C y-1), area 13.8-15.2x106 ha). For the reasons just mentioned, estuarine productivity is difficult to estimate. Their overall floristic composition is sometimes not that dissimilar to that of inland salt vegetation, with which they also intergrade; indeed, some European inland salt vegetation may have connections with vegetation that bordered the Tethys Sea (Chapman 1974; see also above). C4 and some C3 Poaceae (Flowers & Colmer 2008; Bennett et al. 2013) and chenopod Amaranthaceae, also often C4 plants, are notably common in salt marshes and inland salt vegetation, but Plumbaginaceae, Caryophyllaceae, Aizoaceae, Frankeniaceae, Nyctaginaceae, Tamaricacaceae (all Caryophyllales), Cyperaceae and Juncaceae, also Restionaceae (all Poales), Juncaginaceae (Alismatales), as well as Primulaceae and some Asteraceae (sometimes prominent in degraded saltmarshes) may also be appreciable elements of the vegetation (Chmura 2011; esp. Chapman 1974). All told there are some 350 species of halophytes (Flowers et al. 2010). Like vegetation dominated by sea-grasses, salt marshes actively trap sediments (Marani et al. 2013 and references). Estimates of carbon burial in salt marshes are given by Mcleod et al. (2011), which, they estimate, occupy 2.2-40x106 ha: the rate of burial is (194-)218(-242) g C m-2 y-1 (range 18-1713) and total carbon burial is 4.3-96.8 Tg C y-1. Duarte et al. (2005) estimated that salt marshes occupied ca 40x106 ha with a gross primary productivity of some 3595 gCm2y-1 and global primary productivity is 1438 TgCy-1, while their net ecosystem production was 1585 gCm2y-1 and globally 634 TgCy-1, substantially higher than either mangrove or seagrasses. They estimated C burial to be 60.4-70.0 TgCy-1. Discussion.
Although grasslands, mangrove vegetation, and the like are treated above as if they are fixed and invariant communities, their extents, and the roles that individual species play in them, change over time. Thus the grassland biome that is now such a prominent feature of the vegetation globally can be dated to the Pliocene, within the last 10 m.y. or so, and especially within the last 3 m.y., even if its inception was considerably earlier in the Tertiary (Sage et al. 2012). Grassland remains a dynamic entity, some projections suggesting the importance of increasing atmospheric CO2 concentrations, with C4 grasses being susceptible to replacement by C3 grasses (e.g. Collatz et al. 1998). Mapping of post-glaciation forest changes shows that some species have been fairly constant in abundance, if not in location, but they are mixed with other species that as it were appear from nowhere and come to be abundant over wide areas (e.g. Webb 1988; Williams et al. 2004; see also Jahn 1991). Plant communities come and go, and the relation between present, past and future is unclear (e.g. Torres et al. 2012). Furthermore, much of the earth's surface has been profoundly modified by the activities of humans, to the extent that the figures given above for the areas occupied by different vegetation types have changed greatly over the last 10,000 years - hence, in part, the differences in some of the estimates above (Dixon et al. 1994). Thus the area occupied by mangroves has decreased greatly because of cutting, yet that of salt marshes may have increased because of land clearance and the resultant increase in sediment in rivers (e.g. Spalding et al. 2010; Kirwan et al. 2011; Chmura 2011 - see also above). Similarly, there was ca 1/3 loss in biomass in primary - but obviously not untouched - forests in Peninsula Malaysia over a single decade late last century (Kerridge et al. 1987; Dixon et al. 1994 and references). The focus here is on pre-agricultural vegetation, although one could well argue that as soon as humans started using fire, they began to instigate profound vegetational changes. Clearly, one has to guard against over-simplification and reification. Thus the relationship between mono- or oligodominant tropical forests in particular and the fungal associations of the trees in them is not simple. As noted above, not all monodominant legumes, for example, are ectomycorrhizal (Torti & Coley 1999; Torti et al. 2001), nevertheless the combination of phylogeny, monodominance and mycorrhizal type in legumes is strong. Of the nine dominant tropical species listed by Hart et al. (1989), five are ectomycorrhizal Detarieae, and two more are "caesalpinioid" legumes, while all the dominants listed by Connell and Lowman (1989) were legumes. Again, although I have separated mangrove and sea grass-dominated communities, members of both are halophytes, that is, plants tolerating at least 200mM salt. They integrade with estuarine and also inland halophytic vegetation, the former with abundant Poales, especially Poaceae, the latter often dominated by Caryophyllales; in both the latter C4 plants are common (Flowers et al. 2010). In the more ecophysiological interactions under discussion here, one or a few clades largely dominate important aspects of community/ecosystem functioning. Although there are suggestions that the total standing biomass of the trees in forests is invariant with respect to species number and composition or to latitude (Enquist & Niklas 2001; Enquist et al. 2007; but c.f. e.g. Dixon et al. 1994), above- and below-ground biomass, nutrient cycling and productivity all vary considerably. The ecosystem functions emphasized are carbon sequestration and primary productivity - the two are of course not necessarily linked. In general, carbon estimates are of above-ground biomass, or that in soils and peats, and in the latter in particular it represents over half the total forest carbon pool (Dixon et al. 1994), with sequestration times being relatively long term. In many speciose tropical lowland rainforests, which have barely been mentioned here, productivity is high, standing carbon biomass is high, below ground biomass is relatively low, and carbon sequestration times are short (e.g. Dixon et al. 1994). Communities dominated by ectomycorrhizal trees, particularly those in the boreal zone (Dixon et al. 1994) all sequester considerable amounts of carbon in their soils. However, the rate of nutrient turnover in mono- or oligo-dominant terrestrial vegetation types varies. It can be very high, particularly in those in the tropics (Torti et al. 2001), and the mono- or oligo-dominant woody vegetation there is not always species-poor, as White (1983) noted for Miombo vegetation and Beard (1946) for the Mora-dominated forests of Trinidad; the dipterocarp-dominated forests at Bukit Lambir, Sarawak, are among the most species-rich tropical forests anywhere (Lee et al. 2002). Interestingly, Mora in particular behaves like some conifers (Enright & Ogden 1995; Aiba et al. 2007) and is almost an add-on to the vegetation, communities with and without Mora being otherwise similar; similarly, emergent dipterocarps may form a separate stratum above the rest of the forest (see Ashton & Hall 1992). As noted above, sea-grass, salt-marsh and mangrove and to a somewhat lesser extent grassland vegetation are all very productive and all sequester considerable amounts of carbon. In many cases, communities in which ECM clades dominate grow under quite extreme environmental conditions, whether of substrate or climate. Thus Brodribb et al. (2012) noted that the ectomycorrhizal Pinaceae (as well as other Pinales, which are endomycorrhizal), successfully competed with angiosperms, but not in the most productive environments, while the marine and estuarine environments inhabited by mangroves and sea-grasses are physiologically quite extreme for angiosperms. The dominance of a relatively few groups of plants, particularly marked as one proceeds polewards, perhaps reflects the relative rarity of successful adaptations to more extreme conditions; that is certainly true of the adaptation of angiosperms to the submerged marine environment, and this may contribute to the obvious but still puzzling (from the causal point of view) latitudinal gradient in diversity (Fischer 1960). Communities growing in more extreme conditions tend not to be species-rich. Of course, as with just about all features of angiosperms, the physiological/ecological traits under discussion have evolved several times, although all have a strong phylogenetic signal. The clusters of origins of C4 photosynthesis in the PACMAD clade of Poaceae, and again in Cyperaceae and in Amaranthaceae (e.g. Kadereit et al. 2012), and the origins of adaptations to life in saline habitats, even submerged in the sea, in the Alismatales, suggest further complexities underlying the evolution of some of the traits. Even ECM clades have originated many times in the N-fixing clade, even if exactly which caesalpinioid legumes in and around Detarieae are ECM plants is unclear. There are a number of independent adaptations to the mangrove habitat, yet both Rhizophoraceae-Rhizophoreae and Arecaceae-Nypa are particularly important here. This compares with the phylogenetic signal in the woody plants adapted to environments in extensive ecosystems like the South American Cerrado vegetation (Simon & Pennington 2012) and the underground forests of Africa (White 1976), which, if present, is small. An analogy with the related ideas of keystone species and ecosystem engineers, species that directly or indirecty disproportionately control resources needed by other organisms (Wright & Jones 2006), may be helpful here. The clades involved have ecological effects much larger than might be expected from the number of species they contain (e.g. Leighton & Leighton 1983; Terborgh 1986; Power et al. 1996; Watson 2001; Watson & Herring 2012). Thus Brodribb et al. (2012; see also Coomes & Bellingham 2011) thought of conifers in general as being ecosystem engineers because of their major effect on the environnment. Whether keystone clades or ecosystem engineers, I do not suggest that the clades being discussed are sharply distinguishable from all other clades in terms of their effects on the environment (for demolition of the simple idea that there are keystone species - species "important for something", see Hurlbert 1997), nevertheless, they have major effects at ecological scales from the local community up to the global ecosystem. These keystone clades are associated with major biomes or ecosystems (Pennington et al. 2004; see other papers in Proc. Roy. Soc. B, 359 (1450). 2004), and it is at this level that the ecological interactions of these clade play out. It is increasingly a matter of comment that a number of clades seem to be more or less restricted to biomes (e.g. Schrire et al. 2004; Pennington et al. 2009; Dick & Pennington 2011; de Nova et al. 2012). In such cases ideas of phylogenetic biome or niche conservatism are invoked: Clades retain niche-related traits or, more generally, have conserved ecological roles (e.g. Wiens & Donoghue 2004; Crisp et al. 2009; Crisp & Cook 2012; B. T. Smith et al. 2012). However, as Mouquet et al. (2012) note, the term "phylogenetic conservatism" has been used in various ways in the literature on phylogenetic community ecology, so, as with keystone species, its use may generate more heat than light. The emphasis on small groups of species with a disproportionately great influence on global ecology raises the issue of how species-poor ecosystems in which they often grow function over time. There may be phylogenetic complementarity if such ecosystems include members of different clades of ECM plants, even if there there is little obvious ecological complementarity (c.f. Cadotte et al. 2012); perhaps Salicaceae, Betulaceae and Pinaceae in Boreal forests interact in this way. Studies suggest that even if dominant species can maintain ecosystem functioning in the face of the loss of rare species, at least for a time (e.g. Smith & Knapp 2003), phylogenetic diversity improves ecosystem functioning, although this also depends on rainfall, temperature, levels of soil nutrients and CO2, etc. (see e.g. Chapin et al. 1997; Zavaleta et al. 2003; Maestre et al. 2012; Cadotte et al. 2012). Indeed, experiments measuring biomass production find that productivity and diversity become more closely linked over time (Reich et al. 2012); as conditions change, different species may assume importance - and of course the history of the Tertiary is one in which conditions have never been fixed for long. At the same time, although some work suggests that there is evolutionary flexibility in the role that species play (Aizen et al. 2012), other studies suggest that there is conservatism (Maherali & Klironomos 2007; Stouffer et al. 2012: see above). However, it should be emphasized that little of the work on community/ecosystem functioning, other than some on grasslands, has emphasized the kinds of communities that are the focus here, certainly not the species-poor communities like that of sea-grasses. Estimating the long-term ecological importance of the groups under discussion is difficult. Some changes in floristic composition, however caused, may have little effect on community functioning. Although the species of trees growing in eastern deciduous forests in the eastern North America have changed considerably - and continue to change - in response to logging pressure, changing fire regimes, etc., since the advent of Europeans, the dominant species have remained ECM plants (Abrams 1996, 2003). Thus many recent changes in these forests have been in the relative abundance of different ECM species, although with the suppression of fires in the last three hundred years or so replacement of oak-pine forests by largely non-ECM species seems to be under way (Abrams 1996, 2003). Similarly, although the forest dominated by American chestnut, Castanea dentata, disappeared last century, much was replaced by mixed oak or oak-hickory forests (Abrams 1996), so the forests remain dominated by ECM trees. The extent to which the ECM-dominated Mediterrananean Maquis vegetation reflects human activity is unclear, but the major components of the different successional stages are all ECM plants (Comandini et al. 2006). The ages of the clades are usually much more than 10 m.y., and so their ecological conservatism is relatively ancient, but this does not convert in any simple fashion to major ecological effects of comparable antiquity. Thus C4 photosynthesis may have originated in the Oligocene ca 33 m.y.a., but C4 grasses became diverse - and made a corresponding major contribution to overall vegetation biomass - only in the late Miocene 9-8 m.y.a., the process being complete as recently as the late Pliocene 3-2 m.y.a. (e.g. Edwards et al. 2010; Strömberg & McInerney 2011; McInerney et al. 2011; Strömberg et al. 2011; Arakaki et al. 2011; Sage et al. 2012). In the late Eocene mixed deciduous broad-leaved and evergreen and deciduous conifer forests grew within both the Arctic and Antarctic circles (e.g. Collinson 1990; Jahren 2007; Harrington et al. 2011; Collinson et al. 2012; Pross et al. 2012). ECM plants [to add] Normapolles pollen, commonly associated with Fagales, was abundant in the Turonian-Campanian of the
Cretaceous, some 94-80 m.y. before present, peaking in the Coniacian-Santonian ca 88 m.y.a., and occurring in much of the Northern Hemisphere in the area 20-45oN (Cretaceous palaeolatitude: Kedves 1989; Sims et al. 1999; Friis et al. 2003a, esp. 2006a). Nothofagus-like pollen (Nothofagites) characterized southern temperate Gondwanan areas during the later Cretaceous (Nichols & Johnson 2008). When we stop to consider the implications of these asymmetries in relationships between animals, plants, and the environment, we can see that species numbers per se are but one way of thinking about seed plant evolution. By focusing on the construction and maintenance of the ecological scaffolding of community structure over evolutionary time and in a phylogenetic context, angiosperms with dense venation, C4 grasses and ectomycorrhizal plants represent pillars, and ants, bumble bees, fruit bats and the like, arches and spandrels. These groups appear to has/have had a major role in constructing and maintaining the environment, while the bulk of the tens of thousands of species of the [asterid I + asterid II] clade make up the paintings in the spandrels (apologies to Gould & Lewontin 1979). These paintings are forever changing as individual species go extinct, for instance because of the breakdown of plant/pollinator relationships, while other relationships are evolving. Over time the whole biosphere has changed as groups of plants with different eco-physiological capabilities assume prominence, and this helps provide the context for the diversification of seed-plants, and of their associated animals, at all levels. Gorelick (2001) summarized some twenty hypotheses that have been advanced to explain diversification/success of the angiosperms (see also Crepet & Niklas 2009), many having to do with flowers, and all told some 120 or more hypotheses have been advanced to explain the patterns of species richness that are such a distinctive feature of the environment (Palmer 1994). Work has tended to focus on understanding speciation within individual very speciose clades (e.g. Davies et al. 2004c), and much literature emphasizes the acquisition of "key innovations", apomorphic features of often assumed functional and ecological advantage whose development allowed a subsequent increase in the overall speciation/diversification rate of the clade in which it arose (e.g. Marazzi & Sanderson 2010). Thus clades in which latex (Farrell et al. 1991; see also Powell et al. 1999; Agrawal & Konno 2009: survey of laticiferous plants and latex; Konno 2011: chemistry), nectar spurs (Hodges & Arnold 1995; Hodges 1997; Kay et al. 2006), monosymmetric flowers (Sargent 2004; Kay & Sargent 2009; c.f. in part Kay et al. 2006), humming bird pollination (Schmidt-Lebuhn et al. 2007), animal pollination (Eriksson & Bremer 1992; Kay et al. 2006b), self sterility (Ferrer & Good 2012), or the climbing habit (Gianoli 2004) have evolved, are often more diverse in terms of extant species than their sister clades lacking these distinctive features. On the other hand, Malpighiales and Ericales appear to be disproportionately common among the small trees of the understorey of tropical rain forests (Davis et al. 2005a). They include taxa with many kinds of flowers and fruits, and monosymmetric flowers of a variety of morphologies are scattered in both clades. Neither clade can be well characterised either morphologically or chemically, and key innovations for them are hard to identify, although they may become evident if the focus is turned to smaller clades within these two major groups. Indeed, key innovations that cause the more or less immediate diversification of the clade in which they arise may be individually less important than we might like to think, and identifying key innovations is far more than simply linking a feature to a named node (e.g. Sims & McConway 2003; Davies et al. 2004a; Donoghue 2005; Erkens 2007; Crepet & Niklas 2009; Marazzi & Sanderson 2010; c.f. Endress 2011a). Determining that an innovation might be a key innovation is a difficult process (e.g. Cracraft 1990; Sanderson 1998; Ree 2005b; Maddison et al. 2007). There are several related issues. 1. The increase in speciation that results from the acquisition of a key innovation has to be distinguished from simple radiation of a clade when it moves into in a new area, even if allowing the plant with an innovation to move into new ecological space may be part of the definition of a key innovation (Sargent 2004; Marazzi & Sanderson 2010). Thus in Guatteria much speciation may have occurred only subsequent to its entry into South America (Erkens et al. 2007). Although Howarth and Donoghue (2004, esp. 2005) note possible connections between changes in CYC-like genes and changes in floral form in Dipsacales (CYC-like genes are widely involved in symmetry changes, especially in core eudicots (X. Yang et al. 2012; Preston & Hileman 2012, direct links remain to be established - and linking these changes with diversification is yet another issue. Thus crown-group Valerianaceae may be 60-55 m.y. old (Bell & Donoghue 2005a), but diversification in the Andean paramo, which resulted in ca 1/7th of the species currently recognized in the family, happened less than 5 m.y.a. on the arrival of Valerianaceae in South America (Bell & Donoghue 2005b; Moore & Donoghue 2007, see also Viburnum). It is not obviously associated with the evolution of particular floral (or other) key innovations (see also Richardson et al. 2001). Similarly, rapid diversification of Andean species of Lupinus - where most species of the genus are now found - began only some 1.76-1.19 m.y.a. and probably was driven by the ecological opportunities available in the high altitude habitats there (Hughes & Eastwood 2006; Drummond 2008; Drummond et al. 2012); bumble bees, also immigrants to Andean South America, may have been an important factor in the diversification of these plants (Hines 2008). Finally, in Halenia (Gentianaceae) with its "key innovation" of five nectar spurs, diversification and acquisition of these spurs are not simply linked (von Hagen & Kadereit 2003, see also Gentianella, etc.). 2. Key innovations are rarely simple features, rather, they may involve a complex suite of changes, as with the evolution of vessels and dense foliar venation discussed above. Thus Edwards and Donoghue (2006) suggest that several key elements of the cactus ecological niche were established before the evolution of the cactus life form and subsequent diversification of Cactaceae (Ogburn 2007; Ogburn & Edwards 2009; Nyffeler & Eggli 2010 for information), partly because the resolution of paraphyletic groups helped spread what appeared to be phylogenetically linked characters through the tree (Donoghue 2005). TMoreover, the importance of some changes may be less in the changes themselves, but subsequent changes that they make possible and/or their importance in ecological conditions developing long after their origin; it is the combination of traits or the culmination in the development of traits that is important, rather than any one trait itself (Ogburn & Edwards 2008; Horn et al. 2012: Euphorbia subgenus Chamaesyce; Schranz et al. 2012; see also Stebbins 1951). The evolution of flowers, vessels, the effects of genome duplications, C4 photosynthesis, etc., all seem to fit this model. 3. Just as most angiosperm characters are highly homoplastic, arising in parallel and being lost many times, so are features rarely consistently key innovations. Thus the evolution of a feature such as extra-floral nectaries, as in some Senna (Fabaceae), may be a key innovation, but this does not mean that it always is; the loss of such nectaries may equally be a key innovation in related taxa (Marazzi & Sanderson 2010). Similarly, some wind-pollinated clades are very speciose, most are not. 4. Returning to an issue raised above, in many very speciose clades, including angiosperms as a whole, patterns of clade numbers do not suggest any immediate diversification after acquisition of the putative key innovation. Characters that seem to facilitate diversification but that evolve well before the diversification they are supposed to facilitate are best thought of as exaptions (de Queiroz 2002), and at one level it is clear that this interpretation is appropriate for most of the characters considered to be key innovations of angiosperms or of major clades within it - whether flowers, vessels, or C4 photosynthesis. Flowers may become important in facilitating diversification only with the evolution of bees, with bees themselves also diversifying (Cappellari et al. 2013). Pollen is one reward for bees, nectar is another, and the distribution and morphology of nectaries also needs to be factored in to the equation. Note, however, although bees are quite a diverse group, with some 17,500 species (Michener 2007), particular groups of bees, not notably speciose, play a major role in current bee-plant interactions (see above; c.f. Cappellari et al. 2013). Certainly, simply listing clades or, worse, families, orders, etc., and characters may not be very helpful (e.g. S. A. Smith et al. 2011). Thus almost three quarters of Asteraceae are members of the chemically very distinct Asteroideae. Over four out of five Orchidaceae are Epidendroideae (ca 18,000 species), and much diversification occured in the "higher epidendroids" some (64-)59-42(-36)/(49-)39-34(-22) m.y.a. (Ramírez et al. 2007; Gustafsson et al. 2010). Exactly where monosymmetry is an apomorphy in Asterales as a whole is unclear - and so on. Many families have the basic phylogenetic structure of one (or more) very small clades being sister to a very much larger clade. Parallelism and convergence, homoplasy, are everywhere one looks, even in early land plant evolution (e.g. Boyce 2010). As more becomes known about details of molecular evolution, widespread homoplasy is appearing at this level, too. Understanding developmental/regulatory pathways is important. The frequent reaquisition of woodiness in clades that have become herbaceous may be because elements of the cambial regulatory program remain untouched (Groover 2005; see also Blein et al. 2010: vegetative development). There are elements of common developmental mechanisms involved in independent acquisitions of monosymmetry (e.g. Feng et al. 2006: Fabaceae and Plantaginaceae; Zhang et al. 2010, Malpighiaceae), duplication of CYC genes being involved (see also Damerval & Manuel 2003; Rosin & Kramer 2009; Preston et al. 2011b). Irish (2009) suggests that petals may have evolved several times because of the independent cooption of underlying gene regulatory networks. Parallelisms also occur at the amino acid level as in C4 photosynthesis (e.g. Bläsing et al. 2000; Christin et al. 2007b, 2008b, 2009a; Brown et al. 2011). It is a challenge to think about the evolution of the morphological and other novelties that are the focus here. Heterochrony (the male gametophyte of flowering plants is a good case in point - e.g. see Takhtajan 1976), heterotopy (e.g. Baum & Donoghue 2002), and homeosis (e.g. Mathews & Kramer 2012) are all part of this mix. As Preston et al. (2011b) put it as they summarized aspects of the developmental evolution of angiosperm flowers, "reduce, reuse, and recycle" has been the order of the day, and it seems that old dogs can indeed be taught new tricks (Rosin & Kraemer 2009; Mathews & Kramer 2012). We have tended to think of evolution as the modification of pre-existing form: "Are petals in x really modified stamens?". Now we have the tools to think more about the evolution of novelty, elements of developmental pathways that merge and form new regulatory combinations; Mathews and Kramer (2012) review floral and in particular ovule development across seed plants from this point of view. In this context, the often rather sporadic distributions of secondary metabolites has long been difficult to understand. But as with cambia, the ability to synthesise a particular secondary metabolite having been acquired, it may be switched off easily, but not lost, and so the metabolite can be "reacquired" (e.g. Grayer et al. 1999; Wink 2003, 2008; Liscombe et al. 2005; Albach et al. 2005c; Agrawal et al. 2012). However, in other situations pathways may degenerate and change is irreversible (Zufall & Rauscher 2004). Associations between plant and fungus/microbe in both mycorrhizal and endophytic associations, and/or lateral transfer of genes, may also go some way towards understanding the rather unpredictable pattern of distribution of many secondary metabolites (Wink 2008; Lamit et al. 2009); endophytes may synthesize metabolites normally ascribed to the plant partner. The idea of evolutionary "tendencies" persists (e.g. Endress & Matthews 2012), similar discussions recurring periodically in the phylogenetic literature (e.g. Cantino 1985; Sanderson 1991). Indeed, some phenotypes may be the result of parallel mutations that occur only because of a previous change in the larger clade (see Shubin et al. 2009 on deep homology) and Marazzi et al. (2012) attempt to locate such evolutionary precursors - in this case, extrafloral nectaries in Fabaceae - on the tree. The ability of a plant to form an association with nitrogen-fixing bacteria is a good example (see Fabales: e.g. Soltis et al. 1995b), the clustered origins of C4 photosynthesis in grasses and elsewhere invite a aimilar explanation (see e.g. McKown et al. 2004; Christin et al. 2011a, 2013; Grass Phylogeny Working Group II 2011), as does the origins of various symmetries in angiosperm flowers (Irish 2009; Preston et al. 2009). Genes can be transferred via grafts in host-parasite connections, chloroplasts can move via grafts between different free-living organisms - and perhaps genes may be transferred from live pollen that lands on the stigma, germinates, but does little else (Christin et al. 2012: confirmation needed!), and such phenomena may explain clustering of apparently independent origins of features. The idea of co-evolution, reciprocal (mutual) evolution and speciation, often thought of as occurring in associations like those of pollinator/herbivore and plant, also needs revisiting (e.g. Waser et al. 1996). Floral variation, and species numbers, have remained of central interest to biologists. Stebbins (1970, p. 308) noted that in animals major categories might differ in characters related to survival, while in plants the "flower must become a gihly integrated stucture, with all of its parts precisely adjusted to each other" for cross pollination by animals with specialised habits to happen. Fifty years or so ago plant-pollinator relationships were thought of in terms of mutual co-evolution, with an emphasis on lock and key relations between particular flowers and their pollinators implying 1:1 relationships between the two (e.g. Grant & Grant 1965), and Stebbins (1970), although cautious, conveyed this general idea when he noted that euglossine bees obtained fragrances from orchids, extensive speciation in both being the result, and also wghen he discussed intermediates between different pollination syndromes. Even now all too often study of mutualisms, or of plant-animal relationships in general, still focus on only one of the partners, although there is is evidence of widespread asymmetry in the specificity of relationships (Bronstein 1994), e.g. Johnson and Steiner (2000), Mello et al. (2012), etc.. Recent work suggests that some text-book examples of floral co-evolution, the yucca/yucca moth and orchid/orchid bee associations, have other explanations - in the first case the plants diversified notably before the insects and in the second the insects diversified notably before the plants (Althoff et al. 2012; Ramírez et al. 2010, 2011). In the latter case one can think of plants tapping in to pre-existing sensory biases of their pollinators and manipulating their behaviour (Schiestl 2010; Schiestl & Dötterl 2012; Ramírez et al. 2011; see also Dyer et al. 2012; Wright et al. 2013; c.f. Strong et al. 1984). In the less tight association of aroids with scarab beetles, again the beetles diversified well before the plants (Schiestl & Dötterl 2012). The general idea of co-evolution (see Ehrlich & Raven 1964) has been used to describe many different kinds of evolutionary relationships, which is part of the problem. The term has to be defined precisely when used; certainly, in floral evolution there is little evidence of co-speciation (figs may be an exception - Cruaud et al. 2012ab), and even co-evolution in the sense of reciprocal change of both parties is difficult to demonstrate, especially for events early in angiosperm evolution (c.f. Cappellari et al. 2013); that there has been pervasive if less tightly linked co-evolution is incontestable. The rise to dominance of the angiosperms and the diversification of particular angiosperm clades also involves other organisms - plants, animals, fungi, bacteria - as well as changes in the environment itself, and it is a thoroughly ecological process (e.g. Thompson 1998; Harmon et al. 2009). One has to take into account both intrinsic and extrinsic traits of plants. Along these lines, Lavin et al. (2004) and Schrire et al. (2005) suggest that it is more profitable to think of diversification and distribution of Fabaceae in terms of vicariance of biomes rather than of the classic geographical areas. The area a clade inhabits, especially if it is non-contiguous, may affect diversification (Vamosi & Vamosi 2010, 2011; see also Marazzi & Sanderson 2010 above). Under such circumstances diversity may be limited by ecological factors (e.g. Vamosi & Vamosi 2010), although if the assumption that clades increase steadily in diversity with time is unreasonable (Rabosky 2009; Vamosi & Vamosi 2010), so is the implicit assumption that the environment does not change. Initial angiosperm evolution took place under ecological conditions rather different from those under which they prospered later; then continents were drifting apart, there was increasing carbon dioxide concentration and rising sea levels, and ever-wet tropical humid climates, initially rather restricted, were becoming more extensive. Even if "basal" clades that are now species poor were much more diverse in their early history (Magallón & Castillo 2009 and references), they may have been responding to conditions that are not found today. Angiosperm-dominated vegetation is largely of Tertiary age, so the early Tertiary environment - warmer, less seasonal, few fires - may provide another context for thinking about its evolution. Subsequent Tertiary diversification occurred as temperatures and atmospheric carbon dioxide concentration were dropping, seasonality increasing, and, especially towards the end, fires increasing. Climate has been changing dramatically throughout the history of crown-group angiosperms, spurred by angiosperms themselves and their associated fungi (e.g. Knoll & James 1987; Volk 1989; Boyce et al. 2010); see above. In general, the evolution of flowers, vascular systems, and just about all aspects of plants seems a complex, protracted, and clade-dependent process (e.g. Feild & Arens 2007). Flowers and vessels may not have been of immediate evolutionary importance, at least if judged in terms of numbers of extant taxa in early-branching clades with these features. The initial branches of the angiosperm tree are highly asymmetric in terms of species number in extant clades (see e.g. Sanderson & Donoghue 1994; Magallón & Sanderson 2001); Friis et al. (2006b) emphasized that such clades have long fossil records yet include only a few extant species. These clades also differ from other angiosperms in ecophysiological features. Thus ANITA grade angiosperms have low veinlet densities rather like those of other gymnosperms and ferns, so transpiration rates and hence photosynthetic capacities (Pc) are rather low (Brodribb et al. 2007; Boyce et al. 2009; Feild et al. 2009a; Brodribb & Feild 2010); their vascular anatomy is also unlike that of many other angiosperms (e.g. Sperry et al. 2007; Feild & Thomas 2012). Similarly, distinctions between the nature and arrangement of floral parts that are obvious in say, core eudicots are less evident in members of the ANITA grade, endosperm formation is variable, etc. (e.g. Buzgo et al. 2004; Endress 2005c; Taylor et al. 2008; Friedman 2008b); even anatomical typology is questionable (Field et al. 2000b). As Feild and Arens (2005: p. 402) observed, diversification may well depend "on the fortuitous combinations of a large repertoire of traits" rather than on any particular key innovation (see also Crepet & Niklas 2009 and references; Magallón & Castillo 2009). Overall angiosperm success seems to be in considerable part the result of diversification of individual angiosperm clades with various combinations of characters and responding to various ecological/environmental contexts, and establishing an immediate connection between acquisition of an apomorphy or group of apomorphies and diversification is difficult. Angiosperms show bursts of diversification in separate clades, especially in a number of asterids and monocots (e.g. Magallón & Sanderson 2001; Sims & McConway 2003; Crepet & Niklas 2009), and parallelisms from the molecular level up are pervasive (e.g. Endress & Matthews 2012; Mathews & Kramer 2012 and references). Phylogenetic niche conservatism of adaptations to "major ecological niches" mean that some groups will follow these niches when there is an opportunity (Donoghue 2008; especially Lavin et al. 2004; Schrire et al 2005; Marazzi & Sanderson 2010); adaptation to such niches may not occur very frequently. We have to factor in the major climatic changes in the Tertiary, while extinction, although difficult to document, plays an important role. Thus as recently as ca 30 m.y.a. there were humming birds in Europe (Mayr 2004), and Cyclanthaceae are known from European Eocene deposits (Smith et al. 2008). Both groups are now iconically New World, humming birds being involved in the pollination of perhaps ca 2,000 species of flowering plants there. Species number is only one estimate of "success" in evolution, and there is a weak negative correlation between diversity and biomass produced (Wing & Boucher 1998). Biomass production, primary productivity, etc., can be used as more ecological estimates of success, and the possible evolutionary importance of the features just mentioned are to be seen in the context of the eco-physiological evolution of angiosperms and the environmental changes that resulted. From this point of view, venation density and vascular evolution, in association with other ecological features, have helped shape the evolution of biomes within which diversification has occured. Biome change continues, the evolution of grasslands dominated by C4 grasses within the last 10 m.y. being just one example. We have to accept the evolutionary implications of the clade size:importance asymmetries; from this point of view, at one level, species inequality seems the rule. AMBORELLALES
Melikian, A. V. Bobrov
& Zaytzeva Main Tree, Synapomorphies. Nodes 1:1;
plant dioecious; hypanthium +; nectar from base of P?; A sessile, middle layer of anther wall from both secondary parietal cells; pollen anaulcerate [pore-like, operculum endexinous, margin poorly defined], ektexine cupulate [distinctive undulate, columella-less exine]; ovule 1/carpel, outer integument annular [cap-shaped], nucellar cap 0; embryo sac 9-nucleate, with three synergids, bipolar, antipodal cells die very early, polar nuclei in chalazal region [two-modular]; fruit a drupelet; exotesta and exo- and endotegmen thick-walled, lignified; endosperm triploid. - 1 family, 1 genus, 1 species. Note: Possible apomorphies are now being added throughout the site; they are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned
is unclear. This is because there is very considerable homoplasy for many characters, with with variation within and between clades. Furthermore, basic information for all too many characters is very incomplete, often coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there is the not-so-trivial issue of how ancestral states are reconstructed... Of course, putting apomorphies here is a distinctly dubious proposition, given both the position of the clade and the black hole of ignorance immediately basal to angiosperms. Includes Amborellaceae. Synonymy: Amborellineae Shipunov AMBORELLACEAE Pichon, nom. cons. Back to Amborellales Shrub or small tree; alkaloids?;
cork?; axial parenchyma apotracheal diffuse; (some pits in tracheary elements lacking membranes); pericycle with
hippocrepiform sclereids; mucilage cells 0; petiole bundles arcuate; (stomata anomocytic); ?tooth morphology;
inflorescence cymose; flowers small; P spiral, basally connate, 5-8, with a single trace; staminate flowers: A 6-25, outer adnate to the base of T, vascular bundle branched near thecae; pistillode 0; carpellate flowers: staminodes
1-2; G 3-6, whorled; ovule ± median, pendulous, hemianatropous, sessile,
micropyle endostomal; P persistent, stone surface sculpted; seed coat tanniniferous; n = 13; horizontal transfer of atp1 gene. 1[list]/1: Amborella trichopoda. New Caledonia. [Photo - Leaves, Flower.] Evolution. Pollination Biology. Both insects and wind are effective pollinators (Thien et al. 2003). Stigmatic exudate may cover all the stigmas of a single flower together, and pollination of ovules in more than one carpel from pollen landing on a single stigma is possible, i.e. there is an extragynoecial compitum (Williams 2009). Genes & Genomes. The mitochondrial genome of Amborella contains genes from a number of land plants, including at least three different mosses; such "foreign" genes may migrate to the nucleus (Bergthorsson et al. 2004, but c.f. Goremykin et al. 2009, the evidence for these tranfers perhaps questionable on methodological grounds). Although mitochondrial genomes like that of Amborella are as yet unknown from other angiosperms, sampling is very poor. Chemistry, Morphology, etc. For absence of aluminium accumulation, see Thien et al. (2003). There is no reaction wood, the stems of Amborella tending to sprawl, especially when young; in terms of architectural models (Hallé et al. 1978) the plant conforms to Troll's model. Some pits of the tracheary elements lack membranes, so technically they are vessels; open conduits are made up of only two such cells (Feild et al. 2000b), but Carlquist (2012a, p. ; see also 2012c) thought that these were artefacts, noting that "intact porose pits in end walls of Amborella can be found". Stomatal morphology is quite variable, although the brachyparacytic configuration is common (Carlquist & Scnier 2001). The leaves are
described as being spiral at first (Cronquist 1981; Takhtajan 1997), but c.f. Posluszny and Tomlinson (2003). The perianth is spiral and
undifferentiated. There seems to be no agreement on pollen morphology; Sampson (2000) and Hesse (2001) suggest that
the pollen is not really tectate (see also Doyle 2000, 2001; Doyle and Endress 2000), and the aperture is difficult to categorise, as well as not always being present. Williams (2008, 2009) describes pollen tube development and fertilization. The ovule has been described as being orthotropous, anatropous, or intermediate (Tobe et al. 2000). Bobrov et al. (2005) show that the drupe of Amborella differs from a typical drupe in that the bulk of the woody layer is mesocarpial in origin, unlike the drupes of Laurales, etc. The nature of the "resinous" cavities in the mesocarp is unclear; although not observed by Bobrov et al. (2005), they were conspicuous in material I saw and are unlikely to be an artefact caused by re-expansion of dried fruits prior to study. The seed coat appears to have thin, unlignified walls, as might be expected in such a fruit, although some lignification has been reported (Tobe et al. 2000). Friedman (2006; c.f. Tobe et al. 2000) described a very distinctive embryo sac for Amborella; a third synergid cell arises from a cell division that also produces the female gamete. In other angiosperms the polar nuclei are sister to the egg nucleus (at one end) and the central chalazal nucleus (at the other), and the egg is produced by a nuclear division; however, the overall pattern is not necessarily fundamentally different since Amborella has a 9-nucleate embryo sac (c.f. Friedman 2006). Friedman and Ryerson (2009) discuss the evolution of the angiosperm embryo sac in detail. It is unclear how widespread the "other angiosperm" pattern really is, and in part it may rest on the belief that the micropylar and chalazal ends of the embryo sac are identical, each representing a single, highly reduced archegonium. Porsch (1907) took this view, but he had an "Englerian" concept of seed plant evolution, with Amentiferae being primitive. Porsch and others at that time (e.g. Nawaschin 1895) saw chalazogamy in Amentiferae (see Fagales here, also Ulmaceae) as being in some way intermediate between porogamy and non-angiospermy, where the female gametophyte has more than a single archegonium. Additional information is taken from Bailey and Swamy (1948: general), Metcalfe (1987: anatomy),
Philipson (1993), Sampson (1993: pollen), Floyd and Friedman (2001: endosperm development), Carlquist and Schneider (2001: leaf and stem anatomy), Yamada et al. (2001a: ovules), Posluszny and Tomlinson (2003: floral morphology), Field et al. (2003: ecophysiology) and especially Tobe
et al. (2000: embryology). Chemistry? Previous Relationships. Amborellaceae were included in Laurales by Takhtajan (1981) and Takhtajan (1997).
1E. There are about 330 species of humming birds, all from the New World, and their centre of diversity (ca 1/2 the species) is the Colombia-Ecuador region (Snow & Snow 1980). Some 1,000 species of Ericaceae-Vaccinioideae-Vaccinieae and Gesneriaceae-Gesnerioideae may be pollinated by humming birds, and they, too, have their centres of diversity in the Colombian-Ecuadorean region (Luteyn 2002; Weber 2010); some 250 species of Salvia (Wester & Claßen-Bockhoff 2011), 225 species of Heliconia (Pedersen & Kress 1999), 500-600 species of Acanthaceae (E. A. Tripp & L. McDade, pers. comm.; Tripp & Manos 2006), etc., are also bird pollinated. Some humming birds are migratory, and seven species of these humming birds pollinate ca 130 species of plants in western United States alone (Grant 1994; Grant & Grant 1968). The overall imbalance of pollinator species number:numbers of species of plants pollinated is probably similar to that of the euglossine bees just mentioned. (Map: see Bleiweiss 1998b, area occupied by migratory humming birds alone in blue; localities of fossil humming birds in green.)
