ANGIOSPERM PHYLOGENY WEBSITE, version 13.
On classifications in general, and in particular on the classification used here.
On forming clade characterizations (and thinking about apomorphies).
SUMMARY OF THE SYSTEM (AND LINKS TO MAIN PAGES).
On some poorly-known taxa that are in need of study.
On the organization and design of this site.
On the interpretation of the text, etc.
Important - Warning to All Users!
History of the site.
Website developed and maintained by Hilary Davis: email@example.com
Systematics is a profoundly historical discipline, and we forget this at our peril. Only with a phylogeny can we begin to understand diversification, regularities in patterns of evolution, or simply suggest individual evolutionary changes within a clade. Our recovery of that phylogeny is the recovery of evidence of a series of unique events that comprises the history of life. This series of pages is a set of characterizations of all orders and families of extant angiosperms (flowering plants) and gymnosperms, i.e. all seed plants, as well as many clades grouping families and orders and some smaller clades, especially within larger families. They are designed to help in teaching seed plant phylogeny at a time when our knowledge of the major clades of seed plants and the relationships within and between them are still somewhat in a state of flux, even if much of the broad outline seems clear (see A.P.G. III 2009) and there are facilities developing that allow one to see a daily updated Tree of Life based on genome sequences as they appear, for example (Fang et al. 2013). Indeed, as of ix.2014, I estimate that there are still substantial questions about relationships in about twelve orders of seed plants, less serious questions about five more, and four or more internal nodes/areas where there are also substantial problems, not to mention perennial aggravations such as the positions of taxa like Ceratophyllum and Gnetales . The almost routine analysis of massive amounts of data from choroplast genomes is helping to shed light on relationships in some of these areas, but at the same time the results of analyses of more nuclear data question some relationships that we thought we understood. As details of phylogeny are clarified and new findings made in anatomy, morphology, etc. (far fewer that one would like), they can be rapidly integrated into the Angiosperm Phylogeny Group system that is followed here. Books are out-of-date before they appear, furthermore, there is no comprehensive phylogeny-based treatment of angiosperms, out-of-date or not; D. Soltis et al. (2005b) remains the closest. However, there are useful treatments of the main European families in Sitte et al. (2002), and of North American families in Judd et al. (2007, ed. 3) and Simpson (2010, ed. 2), while Neotropikey (Milliken et al. 2009 onwards) - far more than a simple interactive key - is an invaluable resource for all students of the neotropical flora. The following link takes you to a regularly updated and printable Angiosperm Phylogeny Poster while there is a different visualization of the seed plant universe at Botanical Chart.
The focus of this site is on angiosperm families, although treatments of gymnosperm groups were added in 2005. Emphasis is placed on plant families because they are the groups - admittedly partly arbitrary as to circumscription, but now monophyletic (including all and only the known species of a commonn ancestor) - around which many of us organize our understanding of plant diversity. I also pay attention to groupings of families because much progress is being made in sorting them out, while infrafamilial groups in families like Poaceae, Apocynaceae, Malvaceae and Ericaceae are being added as studies become available. In larger families I tend to focus on literature that deals with clades with fifty or more taxa, in smaller families the coverage is more detailed.
Relationships between families, etc., are shown as branching diagrams or trees; Baum and Smith (2012) provide an excellent account of how to interpret and think about such trees. Indeed, trees are a means to an end. For instance, they can depict what makes clades unique, the synapomorphies or shared derived characters of clades that first appeared in their immediate ancestors. Throughout the site, the treatment of variation is as hierarchical as I can make it, with putative apomorphies being mentioned at the appropriate place in the tree, although in the ultimate groupings, whether family or genus, both apomorphies and characters varying within these groups are mentioned.
However, for the most part our knowledge of synapomorphies associated with the taxa characterised here remains poor. Finding out the composition of clades can be easier than finding the synapomorphies for the same clades (see the discussion below). And even knowing about synapomorphies is still only the beginning of understanding the whys and wherefores of the evolution and diversification of seed plants, our ultimate goal. Hence most families include a section on various aspects of their evolution, with sections including "Divergence & Distribution", "Bacterial/Fungal Associations", "Plant-Animal Interactions", "Pollination Biology & Seed Dispersal", and "Ecology & Physiology". There is also a separate and more extended discussion on the evolution and diversification of angiosperms as a whole that is being developed, and here in particular the emphasis is less on species numbers, more on what species/clades "do", how plants play a major role in constructing the environment in which they (and we) live.
Further information about all families mentioned on this page may readily be found by using the "Families" link in the top bar, even if no direct links are provided here (sorry); information about characters mentioned may also be found in the characters page.
ON CLASSIFICATIONS IN GENERAL, AND THIS CLASSIFICATION IN PARTICULAR
On classifications in general
Godfray and Knapp (2004: p. 562) observed that "users want stable, informative and accessible classifications that enable easy identification" - although invoking "users" without specifying those who make up this group rather begs the question. The classification here is for all interested in comparative biology, hence the emphasis on monophyly; there are, as we shall see, many ways of making such a classification accessible to all.
Classifications in the broad sense are box-in-box, group-in-group, or part/whole naming devices that we use to communicate aspects of our knowledge of things in general (see Parsons & Wand 2008 for an introduction). For any classification system to be effective, it must be stable, universal (i.e., be used by a wide range of people), and it must enhance communication of knowledge by helping us to relate things in our minds, and from this point of view biological classification systems are no different from any others (Stevens 2006a for references). The phylogeny-based classification used here conveys aspects of our knowledge about the phylogenetic relationships about land plants. Thus a family is clearly flagged as such and is a monophyletic group that can contain several genera, also flagged as such and also for the most part monophyletic, but a genus can never include families. Generic, family, etc., names are simply words we use to denote appropriate parts of phylogenies and convey some, if rather minimal, information about their relationships. Note that the circumscription of individual taxa may as much reflect the fact that the birthplace of contemporary systematics was Europe and North America, not the Antipodes (e.g. Walters 1961), rather than any philosophical ideas of the authors describing these taxa (some nineteenth century botanists were aware of this local, eurocentric bias).
Here I use what may be called a flagged hierarchy (Stevens 2006a) for naming taxa. The rank terminations used (-ales, -aceae, etc.) suggest relative inclusion relationships of groups of species in the local hierarchy - seed plants. If we are talking about a monophyletic group, say Ericaceae, and Vaccinioideae are mentioned, then the latter must refer to a clade contained within the former, even if neither are automatically comparable with Polemoniaceae and Cobaeoideae, or any other similar family-subfamily combination. All are monophyletic groups, but that is all they have in common. Taxa at the same rank are equivalent only by designation and have nothing necessarily in common other than their monophyly. Rank as used here has no meaning other than signifying a monophyletic group that includes other monophyletic groups with appropriately subordinate rank terminations. Even sister taxa have only age and the fact that they ultimately descend from an immediate common ancestor necessarily in common.
Valentine and May (1996), on the other hand, think of the Linnaean hierarchy as an example of an aggregative hierarchy (close to the class hierarchy of Stevens 2006a); for them such aggregative hierarchies have emergent properties, while they dismiss phylogenies as being simply positional structures lacking emergent properties (for hierarchies, see also Eldredge 1985; Salthe 1985). Indeed, rank terminations have relatively infrequently been used to denote absolute rank, although Linnaeus (at least in theory) at the level of genus and species may be such an example. (Classifications where rank is absolute, taxa at the same rank being comparable entities, are class hierarchies in the strict sense - Stevens 2002, 2006a).
A flagged hierarchy is useful in memory and communication (e.g. Stevens 2006a). It improves memorization by tapping in to the hierarchical structure of language (an extension of the noun-adjective structure of binomials); emphasis on gener, families and orders, as here, is simply a didactic device. Genera (most), families, orders, etc., are monophyletic units useful in communication, units that for the most part include largish monophyletic groups of species and that are used in general conversation by biologists and others world-wide.
The distinction between grouping and ranking is extremely important, as is how we interpret rank. We can both agree that there is a genus Acer, yet disagree as to whether it should be in Aceraceae or submerged in Sapindaceae. Although from one point of view this disagreement is utterly trivial, it can have profound consequences if we misunderstand the nature of the classificatory hierarchy. Taxa at the same rank are unfortunately sometimes treated incorrectly as if they were equivalent by biologists attempting to understand evolutionary or biogeographic problems (e.g. Ricotta et al. 2012), even if those constructing the classifications were explicit about the non-equivalence of such taxa (see Darwin 1859; Stevens 1997; Bertrand et al. 2006).
Turning more specifically to phylogenetic classifications in general, and to the particular classification used here, Backlund and Bremer (1998) provide a very useful discussion on the principles of phylogenetic classification that is applicable at all levels apart from species. The zoologists Vences et al. (2013) list classificatory principles that are largely in agreement with those of Backlund and Bremer (1996) and those followed in this site, although they are rather more favourable to having small genera that I am - but this is perhaps partly because the groups on which they focus are small compared to those under discussion here. See also Stevens (1998), Albach et al. (2004), Entwisle and Weston (2005), Pfeil and Crisp (2005), Pauly et al. (2009), The Legume Phylogeny Working Group (2013b), etc.; many other papers are mentioned in the "Classification" section at the end of each family discussion.
Most importantly, taxa that are recognised formally should be monophyletic, that is, they should include all and only the descendants of a hypothesized common ancestor. However, this does not indicate which particular clades we might wish to name as families, genera, etc., and talk about in general conversation: If a well-supported hypothesis of monophyly is a necessary prerequisite for a group to be named, it is not a sufficent prerequisite (but c.f. the PhyloCode - Cantino & de Queiroz 2006). Additional criteria should be invoked. Other things being equal, it is helpful if 1, taxa recognised formally are easily recognizable, 2, groups that are well-established in the literature are preserved, 3, the size of groups is taken into account, numerous small groups having little to recommend them since individually they summarise little information and tend to clog the memory, while groups that are too big may be amorphous, and 4, nomenclatural changes are minimized (Backlund & Bremer 1998). The broader phylogenetic context should also be taken into account, that is, formal recognition of a taxon may necessitate the recognition of additional taxa at that rank if, for example, there are several pectinations immediately below that taxon that will also have to recognized at the same rank (e.g. Stevens 1998). Examples are the proliferation of small families in Dipsacales if Valerianaceae, Dipsacaceae, etc., are maintained (see the broadly-drawn Caprifoliaceae here), and the proliferation of genera ensuing from the piece-meal dismemberment of Spermacoce (Rubiaceae) are examples. This emphasizes that it is useful/essential to understand the broader phylogenetic background when names are changed.
The accessory principles of Backlund and Bremer (1998) should be used in combination. Thus keeping the monogeneric Platanaceae separate from their sister taxon, Proteaceae, is justifiable: Both are much-used names that signal well supported, well defined and easily recognisable groups that have long been recognised as distinct, and both have several synapomorphies and do indeed look very unlike each other. Combining the two would yield a clade with few obvious apomorphies, not to mention the fact that Nelumbonaceae should by the same logic (it is also monogeneric) also be included in the expanded family. On the other hand, it is difficult to justify the continued recognition of Callitrichaceae or Hippuridaceae, monophyletic and distinctive although they may be. If they were recognised, several poorly characterised clades would also have to be carved out of Plantaginaceae in any classification that aimed to convey a comprehensive view of the world's flora (see also Pfeil & Crisp 2005; Orthia et al. 2005; Albach 2008, etc., for good practical discussions of such matters). But there are no absolute guidelines. Podostemaceae are sister to Hypericaceae, and here some dismemberment of Clusiaceae s.l. allows the continued recognition of the very distinctive Podostemaceae. Hence the recognition of Hypericaceae as well as Calophyllaceae and Clusiaceae below; the families can all be recognized, and the name Podostemaceae in particular is very well established. A somewhat similar situation: If Lemna and its relatives are a clade sister to most other Araceae, "should" they be recognised as a separate family? Gymnostachys, a phenetically fairly distinctive taxon, as well as the less phenetically distinct Orontioideae would have to be recognised as a separate families (or combined as a single family), too, but Araceae in a somewhat restricted sense would be somewhat more morphologically coherent, although not greatly so, yet not so notably distinct... However, it is in the very nature of such decisions that they are ultimately somewhat arbitrary and unsatisfactory. The emphasis here is on consensus classifications, and on classifications as simply being a means to an end, not an end in themselves.
It is sometimes suggested that taxa at the same rank have a similar degree of morphological and/or molecular differences, or are based on similar characters, or are similar in these respects to taxa elsewhere in a larger clade under consideration (Heenan & Smissen 2013 for an example). This can lead to name instability if used in taxa where such criteria had not previously been used, especially if attempts are then made to extend such criteria beyond any local group of interest, and they may also imply that taxa at the same rank are equivalent (for an example, see Fritsch et al. 2008). It has also been suggested that rank could be made to reflect the age of the clade (e.g. Hennig 1966). Dating the times of divergence of clades is still a very difficult enterprise, and if age as a ranking crierion were introduced, huge disruptions to the names that we use would result. In this context, some recent proposals which invoke the use of age in classifications focus more on providing a standardized timeclip, i.e. set of letters referring to a particular geological period, that can be added to a conventional taxon name (Avise & Mitchell 2007; Avise & Liu 2011; see also Vences et al. 2013).
A useful distinction can be drawn between crown groups and stem groups. The former are the monophyletic groups that include the extant members of a clade, their immediate common ancestor (see the figure below), and also any fossils that are to be placed in this part of the tree. The groups characterized in this site are such groups. Thus Proteaceae are crown group Proteaceae, apomorphies like the single carpel, four-merous perianth, etc., being found in this common ancestor. Stem groups, on the other hand, include all the members of a clade below the crown group to immediately after its split from its sister group - and of course, all branches of this part of the tree. Thus stem Proteaceae would include everything after the split from its sister group, Platanaceae, but they would not be the Proteaceae of these pages. Obviously, most of the organisms in that part of the tree are unknown, only a few fossils being placed there, and it is also not known when/where particular apomorphies of crown group Proteaceae evolved along this branch. In the case of the stem group of angiosperms, not only is it largely unknown, but almost certainly most of the organisms to be placed along it will be gymnospermous.
Problems with this emphasis on monophyly may be caused by reticulation events such as endosymbiosis, lateral gene transfer (see e.g. Dunning Hotopp et al. 2007; Boto 2010 for literature; F.-W. Li et al. 2014) and hybridization, but the first two, at least, are unlikely to be common confusing factors here. The major endosymbiotic events that characterize the clade of which flowering plants are a part (and gave rise to chloroplasts and mitochondria) are very ancient and cause no problems for the student of multicellular organisms, indeeed, patterns of subsequent movement of genes from the mitochondrion and chloroplast to the nucleus can be of phylogenetic interest in land plants. Substantial lateral movement of mitochondrial genes in particular can occur in some host-parasite relationships such as Tetrastigma-Rafflesia (Xi et al. 2012a; Yoshida et al. 2010), via chloroplasts in grafts (Stegemann et al. 2012: exchange between Nicotiana), and possibly via the pollen in situations that do not involve hybridization (Christin et al. 2012). Here, too, there are no major problems, providing one is careful, since the genome in such cases seems to be overwhelmingly from one source; such transfers do, however, raise all sorts of interesting biological questions (see Richardson & Palmer 2007 for a summary). Gene transfer also can occur in less well understood situations such as between Amborella and its epiphytes (Rice et al. 2013).
However, hybridization occurs frequently in seed plants. Genome duplications - hybridization is one cause of them - are common, and are a major driver of seed plant evolution. Duplications have occurred at various times during the evolution of seed plants, and also include palaeopolyploidy events within e.g. Lauraceae, Magnoliaceae, and Poaceae (e.g. Soltis et al. 2009; Litt 2013 for a summary). Most of these do not currently pose major problems for either phylogeny reconstruction or the adoption of monophyly as the major criterion for groups to be recognised formally in phylogenetic classifications, certainly for most genera and above.
Indeed, it might seem simplest to peg genera to above the level at which hybridization is at all common, which one generally thinks of as being between species, only very rarely between genera. One might wish that life were so simple. Thus in Poaceae-Pooideae-Triticeae there are some intractable problems where extremely well established common usage and the principle of monophyly are likely to remain at odds. Many genera there are certainly not monophyletic, being allopolyploids, and the genera are ultimately based on different genome combinations (Dewey 1984; Löve 1984; Brassac et al. 2012: Barkworth 2000 for a history of Triticeae classification; Petersen et al. 2006). There is also extensive reticulation reported within Danthonioideae (Pirie et al. 2009) and Bambusoideae (Triplett et al. 2011, 2014; Y.-X. Zhang et al. 2012; H.-M. Yang et al. 2013), as well as increasing evidence of old hybridization events elsewhere in flowering plants that at the very least cause discordance between relationships suggested by different genomic compartments, as in Smedmark and Anderberg (2007: Sapotaceae) and Fehrer et al. (2007: Asteraceae-Lactucoideae), Y. Liu et al. 2013: -Lactucoideae, perhaps Crepidinae x Lactucinae), Pelser et al. (2008, 2010: -Asteroideae), and Tripp et al. (2013b: Acanthaceae-Acanthoideae, Acantheae x Justicieae). Such reports are becoming more common as nuclear genes are used more frequently, and the chloroplast genome, morphology, and the nuclear genome may suggest conflicting relationships.
Even if classifications can follow morphology, the principle of monophyly is infringed. Wheeler (2014) suggests ways of dealing with such situations, at least if they are fairly simple. A taxon A can be recognised that indeeed includes all the descendents of a common ancestor, even if one of these is the result of a hybridization event with a member of its sister clade, clade B (a situation dubbed epiphyly). When recognised formally as taxon B, this sister clade will then necessarily include all descendents of a common ancestor bar the one involved in hybridization with the member of clade A (= periphyly). Another alternative might be to recognise the clade that results from hybridization as a separate taxon at the same level as the remains of clades A and B - both would then be periphyletic and the "hybrid clade" would be polyphyletic. However, scenarios suggested for hybridizations may be very complex, for example, in Bambusoideae hybridizations involve members of fairly deep clades of which there are no extant diploid members (e.g. Triplett et al. 2014 and references).
Species, however, may be somewhat different, furthermore, many would still suggest that they represent some sort of reality in nature. Indeed, in a number of genera like Medicago relationships at the species level are turning out to be highly reticulating (Maureira-Butler et al. 2008), members of the one species of Senecio and Elymus may have more than one origin (Yan & Sun 2012). There are many problems if one tries to apply a concept of strict monophyly to species, and for many - but not all - biologists to invoke strict monophyly would be inappropriate here (e.g. de Queiroz 1998; Funk & Omland 2003; much of the discussion in Hörandl 2006).
Thinking of aspects of number and size of groups recognized, findings in ethnobiology and cognitive psychology can be used to suggest that a moderate number - probably fewer than 500 - of families is a reasonable goal at which to aim, and that groupings of taxa throughout any system should be rather small in size (e.g. Berlin 1992; Stevens 1994, 1997). Major systems such as those of Linnaeus and Bentham and Hooker were constructed explicitly so as to ease the burden on the memory, the latter in particular ensuring that all groups in their classification were relativeley small, often containing three to eight immediately subordinate taxa - but by no means all their groups were formally named (Stevens 1997, 2002; see also Scharf 2007; c.f. in part Vences et al. 2013). Along the same lines, Burtt (1977b) suggested that the number of names at any rank should be at most one third of those at the immediately lower rank - and monotypic taxa might not need formal names (Burtt 1977b). Consistent with such ideas, a fairly broad view of families and orders is taken here whenever the constraints of monophyly and other criteria used when constructing classifications (see above) permit. Indeed, there is a principle from evolutionary classification that is quite useful here: The size of the gap between two groups tends to be inversely proportional to the sizes of the groups involved (Davis & Heywood 1963). In some situations a large group is formally divided even although the distinguishing characters of the two parts are weak, whereas a smaller group that is similarly divisable may be left intact.
Takhtajan (1997) suggested that smaller families are more "natural" than larger families. This is incorrect. Monophyletic groups that include fewer taxa - Takhtajan's smaller families - do not necessarily have more apomorphies than larger groups, although all members of smaller groups are likely to have more features in general in common. They will have more plesiomorphies - features that are apomorphies of the larger clades of which they are parts - in common; and of course, "having more features in common" is one common meaning of "more natural". A group of any size may have apomorphies, and any inverse correlation between size of group and apomorphy number is at best weak - think of all the apomorphies of angiosperms. However, unreversed apomorphies are less common in smaller, more inclusive clades. But by this kind of argument all families should be very small, since then their members will have a great deal in common, and so will be most "natural".
However, the slippery slope ahead is obvious. As families (for example) are split, the relationships evident between the segregates and that were responsible for their being placed in a single family in the first place will seem to necessitate the recognition of a new order, etc., as is evident in Takhtajan's own work - general taxonomic inflation is the result (see also comparable suggestions in a cladistic context for Brassicales in particular - Ronse de Craene & Haston 2006). Such splitting is also questionable when teaching and learning families, since the student needs to understand the system as a whole. Nevertheless, for some genera removed from the families that until now have included them, the phenetic-classificatory-phylogenetic structure in their new home may mandate the recognition of small families. Note that Takhtajan's suggestion that narrowly defined families (better: taxa in general) are more useful for phylogenetic studies may be true, but this is a separate issue. Indeed, I have more than once regretted prematurely combining groups, whether species (in the context of monographic work) or families (in the course of preparing these notes).
Thus there is ultimately no reason other than convention or convenience why any group should not be segregated into several smaller monophyletic groups, or merged to produce a larger unit; we can talk about one large thing, or about several smaller things. Here I follow van Steenis (1978), Philipson (1987b), and others who have questioned the utility of splitting a group when ideas of the relationships of its constituent members have not changed - that is, very good reasons have to be provided for splitting a family if the genera within it remain part of the same clade, rather than belonging to another clade. Thus A.P.G. (2003) broadened the circumscription of Malvaceae because of the para/polyphyly of some of the families that had historically been associated with it (Judd & Manchester 1997; Alverson et al. 1999; Bayer et al. 1999). These families, particularly Tiliaceae and Sterculiaceae, were not at all easy to distinguish, their close relationship had long been conceded (see e.g. Brown 1814), and to some workers, at least, their combination has come as something of a relief. Although most of the larger clades within Malvaceae s.l. remain difficult to distinguish, even with flowers, Cheek (2007) opts for their wholesale and novel dismemberment into ten families; the "very good reasons" for doing this are wanting.
The same principles are of course applicable when it comes to dividing genera. Groups in which there is substantial disagreement over taxon circumscription despite basic agreement over classificatory philosophy include Orchidaceae, Asparagaceae-Scilloideae, Rubiaceae-Spermacoceae. However, little other than a headache is gained by splitting genera such as Drosera and Gnetum as has been proposed (e.g. Doweld 2000). Indeed, if there is well supported phylogenetic structure within a genus, this is not a signal that two or more genera now have to be recognized, even if the new clades are consistent with morphology and have even been recognized as genera in the past. Here it could be argued that the dismemberment of Pterostylis (Jones & Clements 2002b) was somewhat unfortunate (see Janes & Duretto 2010 and Schuitema & Adama 2011 for something close to a reurn to the status quo ante). That a previously unnamed clade is morphologically distinct and has synapomorphies does not necessitate its formal recognition (c. f. Clements et al. 2011). Along the same lines, if a newly-discovered taxon is sister to an existing named genus, this does not mean that a separate genus is needed for the newly described species (c. f. Davis 2002). Humphreys and Linder (2009) provide a well-documented survey of generic concepts in plants which the reader should consult; they note that generic limits (broad versus narrow) have oscillated historically, and that currently larger genera tend to be recognised because studies tend to be on a broader scale than in the past - and broad limits are my preference, too.
Note that invoking "similarity" or "difference" - whether qualified ("considerable similarities", "substantial differences") or not - in a cladistic context as justification for combining or splitting taxa is not a particularly strong argument (see e.g. Cardiopteridaceae/Stemonuraceae - Kårehed 2002c). Similarity and difference can neither be defined precisely, since what may seem to be substantial similarities to me may not to the next person, nor are they likely to be stable as our knowledge of morphology and what might be putative synapomorphies changes.
I might have prefered to merge some families recognised here or split others, but by and large I do not think my own preferences matter very much - and I take the same position with regards to comparable preferences expressed by others. Indeed, the bottom line is that in flagged hierarchies of the kind used here, the limits of any monophyletic unit generally taught and discussed can be established only by convention and consensus (e.g. Stevens 2002, 2006a; Entwisle & Weston 2005; James & Duretto 2010). Given the increasing molecular and morphological support for the outlines of angiosperm phylogeny detailed in these pages, a stable consensus classification based on this phylogeny seems attainable. Indeed, in addition to providing current ideas of relationships of seed plants in a synthesised form, this site is part of an attempt to build such a consensus over taxon circumscription (see A.P.G. 1999, 2003, 2009; Grass Phylogeny Working Group 2001; Mabberley 2008: Hibbett et al. 2007 for a good example in fungi).
Reaching such a consensus is important, since what we know of angiosperm phylogeny allows a very large number of classifications to be based on it, and unfortunately, "nature" does not dictate what the classification should be. All classifications are constructed by humans to communicate particular aspects of groups and relationships, they are means to an end, not an end in themselves, and in this context, the papers by Bob O'Hara (e.g. 1988, 1992, 1993) are still very much to the point. Our goals as systematists are surely to produce robust hypotheses of relationships, to understand the evolution of morphology, and the like - but not to argue ad nauseam whether something "should" be a family or a subfamily, or whether a genus, known to be monophyletic, should be split (or a group of genera, none monotypic but all all monophyletic, should be merged). That way surely lies madness, and worse: The discredit of our discipline.
There are similar issues whatever naming system is used. Thus in phylogenetic naming (Baum et al. 1998 for an example, but c. f. Baum et al. 2004; for the PhyloCode, see Cantino & De Queiroz 2006) an unflagged hierarchy is used in which terminations of names used are uninformative about the relative position of taxa. Unfortunately, this means that such unflagged hierarchies have very serious deficiences as communication devices. They lack one aspect integral to classifications, whether of vehicles, of organisms by local people, or of organisms in the context of a phylogeny - they contain no intrinsic information about the relationships of the group in question to others (e.g. Pfeil & Crisp 2005; Stevens 2006a). Recent suggestions for using prefixes like "Apo-" and "Pan-" to PhyloCode names will, however, allow limited information of this kind to be conveyed, but only as it pertains to individual branches, and current proposals do not even mandate that such prefixes be employed consistently. In any event, such proposals simply prevent the potential tripling of the number of quite different names used to describe different aspects of a phylogenetic tree over those used to name monophyletic groups pure and simple. In general, where n is the number of extant species in a group, the number of clades in such a group = n-1. Other dodges that may help include the use of prefixes and suffixes like Holo-, -formae, -morpha, Eo-, Eu-, and Neo-. (Species will also need names, too; for their names, see e.g. Dayrat et al. 2008; current PhyloCode thought is to leave the naming of species alone for the time being. However, for practitioners of the phylocode the epithet is the only part of the name that must be used.) Of course, if one adopts the principle of phylogenetic naming one indeed does not have to worry about the nomenclatural consequences caused by lumping or splitting; any well-supported clade can be named without affecting the name of more or less inclusive clades.
Importantly, consensus over the clade names commonly learned by students and used in herbaria will always be needed (as in any classification, including evolutionary classifications as well - see Cronquist 1966), otherwise communication will be impeded, yet PhyloCode names in themselves will contain no guidelines as to which should be chosen. The situation is of course more complicated than this. Terminations that convey ideas of rank in a phylogenetic classification can also be used as PhyloCode names - the PhyloCode neither encourages nor discourages the use of such names - however, there they will carry no implications of rank. How they will be used is another matter, of course.
Of course, there are other ways of constructing classifications, and some still prefer evolutionary classifications. There classificatory principles differ substantially from those followed here, e.g. the recognition of paraphyletic taxa is allowed. Evolutionary classifications in general try and combine phylogeny and morphological gaps, although that is no easy thing to do - it is akin to combining chalk and cheese (for an attempt to make this impossible task seem more objective, see Stuessy & König 2008). However, detailed reasons for prefering the taxa that are recognised are rarely given, although "nature" and "natural groups" are often invoked (c. f. Stuessy & König 2008; Stuessy 2010). Some (e.g. Thorne 1976) have suggested that the sizes of gaps between groups at the same rank should be similar, but any principle like this is inherently flawed (see also above) since the sizes of morphological gaps are more unstable than are phylogenetic relationships, and applying the principle across all flowering plants would both be difficult and cause substantial name changes. The basic problem with paraphyletic groups is that users do not generally expect a family to be nested inside another family, a genus within another genus, etc. This flouts the basic principles of classifications of organisms as evident in folk taxonomies and common expectations of language. Thus when I was working on Ericaceae in the early 1970s it was thought that they were very uncommon in Australia, although it was noted that the related Epacridaceae were very common there, and this caused some bemusement. Given that Epacridaceae have been found to be nested well within Ericaceae (see Styphelioideae), the largely language-driven biogeographic problem has vanished.
Note that the meaning of the word "natural" has long been "a group of the kind (usually unspecified) that I think should be recognised", competing classification become ex ipso facto unnatural (e.g. Bather 1927). Its use is rarely helpful, since one has first to find out what its user means; in general, the invocation of "natural" tends to preclude sensible discussion. I prefer not to use the word.
For summaries of commonly used systems, see Brummitt (1992) and Mabberley (2008). New and largely independent systems come out year after year - examples are Takhtajan (1999, 2009), Doweld (2001), Wu et al. (2002), Goldberg (2003), Shipunov (2005 et seq.), Thorne (2007; very elaborate), Heywood et al. (2007), Reveal (2012: also elaborate, devoid of justification), etc. However, even those who allow or promote the recognition of paraphyletic groups (e.g. Grant 2003; Thorne 2007; Heywood et al. 2007) may find a system recognizing only monophyletic groups of some interest; it can provide a rather different understanding of evolution.
The bottom line is that if hypotheses of phylogeny remain stable, we can have a stable classification based on that phylogeny, and then get on with our work, that is, testing the phylogenies we have, elucidating phylogenies in areas where relationships have remained unclear, studying the evolution of morphology, describing species, etc. In this context, the spread of the Angiosperm Phylogeny Group system (see below) and its widespread use in technical literature, also floras (e.g. van der Meijden 2005), dictionaries (Mabberley 2008), more general and popular literature (e.g. Souza & Lorenzi 2012 - the third edition; Spears 2006; Hilger et al. 2010), and in herbaria (Haston et al. 2007, 2009) is gratifying. Returning to Godfray and Knapp's (2004) users of classifications who want a stable, informative and accessible classification that enables easy identification - essentially, they want cake with everything - these pages attempt to satisfy as many of their needs as possible, but without compromising the primary classificatory principle, that of the monophyly of the groups recognized.
On this classification in particular
It would be impossible even to think about a higher-level classification such as this without the advances in our understanding of relationships made by the phylogenetic analyses of molecular data carried out over the last twenty five years. These are coupled with morphological studies that are evaluated in this phylogenetic context. For the dramatic changes in this area, see, for instance, the pessimistic attitude about orders in Davis and Heywood (1963: 107-108); "The most unsatisfactory taxon in Angiosperm classification", they were "indefinable", their circumscription was not fixed, etc. Families, they thought, were likely to be the largest "natural" unit within the mono- or dicotyledons. Indeed, almost three quarters of the orders recognised by Cronquist (1981) are not monophyletic (44/59, monofamilial orders ignored), and most of the orders that are monophyletic are very small (Zingiberales, with eight families, were the largest); for families, the figures are rather different, and only somewhat over one third (81/273) are not monophyletic, although how to treat families in which single genera have been misplaced is difficult. Interestingly, in both cases, non-monophyletic groups were proportionately rather fewer in monocots than "dicots".
Here I very largely follow the Angiosperm Phylogeny Group classification (A.P.G. III 2009). Any differences are not to be interpreted as differences in principle, simply that new phylogenies continue to be published and that this site is designed to provide an overview of current ideas of higher-level relationships of all seed plants. The Angiosperm Phylogeny Group classification is based on relationships evident in the numerous molecular studies that began to appear in the late 1980s, much of it based on analysis of sequences of chloroplast markers (see A.P.G. 1999 for the principles underlying the classification), and much recent phylogenetic work does not contradict the major outlines of the trees used by A.P.G. II (2003) or even A.P.G. I (A.P.G. 1999). Indeed, there have been only minor changes in the composition of the orders, even if the odd genus or even family is turning out to be seriously misplaced - recent examples are Hydatellaceae (from monocots-Poales to Nymphaeales: Saarela et al. 2007), Guamatelaceae (from Rosaceae to Crossosomatales: Oh & Potter 2006), and Perrottetia and Bhesa (from Celastraceae to Huerteales and Malpighiales respectively: Zhang & Simmons 2006). The main changes have been clarification of the relationhips of individual families or groups of families that were of uncertain position, e.g. of Choranthaceae (Moore et al. 2007), Ceratophyllaceae (Jansen et al. 2007), and unplaced asterid II families (Winkworth et al. 2008). However, note that relationships within many of the larger orders are still unclear in part, and as nuclear genes becoime more frequently used, there may be some changes in the very scaffolding of the APG tree (for some intimations of what may be in store, see the study by Sun et al. 2014 on the rosids).
Phylogenies in this site can properly be shown as tree-like representations. Hybridization is being increasingly documented between genera, while there is also evidence for acquisition of host plant genes by parasites (see above), even wider but inexplicable transfer of mitochochondrial genes in plants like Amborella (Rice et al. 2013 and references), and even transfers of nuclear genes (Vallenback et al. 2008). Although these are likely to be exceptions rather than the rule, Sun et al. (2014) suggest that hybridization may be reponsible for incongruent topologies involving major clades of rosids when genomes are analysed separately.
Most trees have been more or less ladderized, which means arbitrarily, but consistently, showing the smaller (in terms of numbers of terminals) sister taxon first at every node, and the sequence follows that along the top of these trees. (Since phylogenetic trees are like mobiles, the only fixed points being the nodes, there innumerable other ways to construct a sequence - e.g. Hawthorne & Hughes 2008.) The result is that the trees here tend to be pectinate. The ladderization may be imperfect, for example, one can see that on the Main Tree asterids and relatives, with sixteen order terminals, follow rosids and relatives, which have eighteen. When reading a book or following a herbarium sequence, pectination, interpreted carefully, has its value (see Haston et al. 2007, 2009). As one reads the terminals of a pectinate tree left to right, adjacent terminals will be separated by a minimum number of apomorphies. Nymphaeales and Austrobaileyales are here adjacent on the tree, but they could be separated by hundreds of families in the sequence without offending any relationships; if adjacent in a book or herbarium, then it is relatively easy to relate their apomorphic characters, but if separated by hundreds of pages, or two floors in a large building, then it is less easy to get anything from the sequence. (Since all orders on this site are preceded by the apomorphies of the nodes immediately below them in the seed plant phylogeny, and because of the linkages that have been built in, this particular problem does not arise here.) So if one wants to justify a particular herbarium sequence to be based on a well-supported phylogeny, it would be to maximize the number of taxa that are both successive branches of the tree and placed successively in the sequence. Since specimens are generally filed under families, the outline of a new family sequence for arranging herbaria can now be suggested (Haston et al. 2009; Waern et al. 2013). This will further help teaching and learning about plants. There are other cognitive and perceptual issues to think about when drawing trees (e.g. Novick & Catley 2007; Novick et al. 2012); wind-blown trees with all the lines oblique, as in the trees here, may unfortunately be less immediately comprehensible than erect trees with all lines either vertical or horizontal.
In cases where the Angiosperm Phylogeny Group (2003) suggested alternatives as to the limits of families, e.g. Papaveraceae in the broad sense or Papaveraceae, Pteridophyllaceae and Fumariaceae, Proteaceae in the broad sense or Proteaceae and Platanaceae, the choices made in A.P.G. III (2009) largely follow common usage, e.g. as in textbooks like Judd et al. (2007) and Simpson (2006), and particularly in the most recent edition of Mabberley's The Plant Book (Mabberley 2008) - itself an attempt to reflect a consensus, the result of taking the opinions of botanists at several meetings. A.P.G. (2009) thus dispensed with alternative classifications, and reasons are given for the choices that are made there. For many the existence of alternative classifications simply confuses, so reaching an agreement over which names/groupings to use when alternatives are possible seems desirable. Note that the authors of names may not always be correct; these still tend to change. For superordinal names, see Chase and Reveal (2009). Some names may be incorrect according to the latest findings of bibliographic sleuths, but I will wait until activities in this area stop before making changes that may be negated by future findings...
As mentioned above, higher-level relationships in general, and the composition of orders in particular, long presented something of a challenge to systematists (e.g. Davis & Heywood 1963), and the limits of orders have historically shown far more lability than those of families. The composition of clades like Apiales, Crossosomatales and Pandanales is decidedly unexpected, however, these higher level clades are generally accepted even in works with different classificatory philosophies (a good example is Heywood et al. 2007). For some clades like Malpighiales, many of the family groupings within Asparagales, etc., attempts to find distinctive characters have largely failed (but see Endress & Matthews 2006a). Interestingly, as with families, some groupings suggested by molecular studies are supported by morphological and/or chemical characters that have long been known, sometimes for over a hundred years (the relationships betweem Pittosporaceae and Apiaceae/Araliaceae are a case in point - Hegnauer 1969b for references). As our knowledge of morphology and chemistry improves we can hope for improvements in clade characterisations and detection of apomorphies at all levels.
In many cases the "new" family limits of the Angiosperm Phylogeny Group (see A.P.G. 1999, 2003, 2009) are not really controversial, although changes from the limits commonly accepted only a decade ago are sometimes quite dramatic (e.g. Wagenitz 1997). Thus the split of the old Saxifragaceae s.l. is necessitated by its extreme polyphyly, as also with Icacinaceae and Cornaceae. Although such groups had long been considered unsatisfactory, there had been no compelling evidence allowing the user to prefer one circumscription over another; now there is. It is generally accepted that the limits of Lamiaceae and Verbenaceae have to be redrawn, and the content of the two has changed considerably - incidentally they are now easier to identify than before, so the decision to recognise the recircumscribed families is not difficult, and if they were not kept separate, much of Lamiales would collapse into a single family... The same is true for Salicaceae and Achariaceae (Malpighiales), two previously small families that have received the bulk of the old Flacourtiaceae. Clade and hence taxon limits do remain difficult in some Malpighiales, but even there clade support is strengthening (Xi et al. 2012b). Indeed, much of the old Euphorbiaceae remains together (see also Wurdack et al. 2004; Davis et al. 2005), but evidence consistently suggests that Rafflesiaceae are part of this clade (Davis et al. 2007), as are also [Linaceae + Ixonanthaceae]. Hence Euphorbiaceae s.l. have been divided, since maintaining them would i.a. entail reducing the iconic Rafflesiaceae to synonymy and the loss of the well-known Linaceae. Relationships in core Caryophyllales, especially around Phytolaccaceae (perhaps somewhat surprisingly) and Molluginaceae (less surprisingly) are still incompletely understood and refashioning of taxon limits will continue as cladistic relationships become apparent (see e.g. Nyffeler & Eggli 2010; Christin et al. 2011a; Brockington et al. 2011). Some groupings in the old Olacaceae and particularly Icacinaceae areas also remain unclear.
Finding the relationships of parasitic and aquatic groups has presented a particular challenge to systematists. Morphologically, some of these plants are so highly modified that interpretation of the plant body in conventional terms is difficult or even impossible. Thus parasitic groups such as Rafflesiaceae were hard to place since both the vegetative body and even the flowers have changed almost beyond recognition. Furthermore, apparently distinctive character combinations like dioecy, extrose anthers, inferior ovaries, parietal placentation, more or less tenuinucellate ovules, and very small (microspermous) seeds are common in parasitic plants (e.g. Renner & Ricklefs 1995). Similarly, in the aquatic habitat neither vessels in particular nor much xylem in general is needed; leaves are highly modified; and water-mediated pollination, if adopted, is associated with major changes in floral morphology. There are also similar morphological problems with many wind-pollinated plants; again, many characters are affected.
In the past, these and other taxa tended to be assigned to groups using a few or even only a single character that seemed to provide evidence of relationships. Add to this the tendency to weight some characters particularly strongly on a priori grounds, and the result was either the recognition of conglomerate taxa such as Amentiferae, Spadiciflorae, Parietales, and Rafflesiales, all of which have been found be highly polyphyletic, or the segregation of families like Plantaginaceae s. str. (now much expanded) and Leitneriaceae (now in Simaroubaceae).
In molecular analyses of parasitic groups, plastid gene sequences may be difficult or impossible to obtain, the chloroplast DNA in particular experiencing extensive gene loss. Gene loss seems to have occured in parallel, yet a core of functional genes remains, probably because of functional constraints (Delannoy et al. 2011). Indeed, in parasitic plants the rate of molecular change in general often being high (e.g. Duff & Nickrent 1997; Nickrent et al. 1998; Caddick et al. 2002a; G. Petersen et al. 2006b; Barkman et al. 2007; Bromham et al. 2103). The inclusion of parasitic taxa in molecular analyses can cause conniptions (e.g. Nickrent et al. 2004; Davis et al. 2004; Chase et al. 2006; G. Petersen et al. 2006b), not least because there can be horizontal transmission of genes (e.g. Davis & Wurdack 2005: Vitaceae to Rafflesiaceae; Barkman et al. 2007: the mitochondrial atp1 gene commonly moves) including the the invasive cox1 intron (Barkman et al. 2007). Molecular change may also be rapid and morphological change extensive in sapromycotrophic (Leake 1994) and carnivorous groups. In general, such groups may show so much molecular change that the problem of long-branch attraction is serious.
But progress is being made. Placements for Rafflesiaceae, Mitrastemonaceae, and Cytinaceae have been suggested (Barkman et al. 2004; Davis & Wurdack 2004; Nickrent et al. 2004; Davis et al. 2007); it seems likely that Burmanniaceae s.l. are polyphyletic, but all parts are to be located in Dioscoreales (Merckx et al. 2006, 2009a, 2010a); and relationships within the largely hemiparasitic Santalales are also being clarified (Nickrent et al. 2010 and references). see also Naumann et al. (2013) or a comprehensive study of parasitic taxa and their evolution (?often beginning in the Cretaceous). Molecular studies are also suggesting that aquatic groups with hitherto problematic relationships may find homes. Thus Podostemaceae are sister to Hypericaceae (Malpighiales: e.g. Kita & Kato 2001), Hydatellaceae, which used to be in Poales, are part of Nymphaeales (Saarela et al. 2007), and Hydrostachyaceae may be close to [Hydrangeaceae + Loasaceae] (Cornales: Xiang et al. 2011), although they have been placed in Lamiales (Burleigh et al. 2009); in the first two cases in particular there are distinctive morphological and chemical features that support the moves. Ceratophyllaceae seem to be finding a position as sister to eudicots (see Moore et al. 2007), but their morphology is so derived that there is no morphological evidence of which I am aware for this relationship.
Given the suggested relationships of some parasitic and aquatic groups, it can be very difficult to understand how they have evolved from their more morphologically conventional relatives, however, it may well be that our preconceptions as to likely or possible evolutionary change are at fault. If Podostemaceae are indeed sister to Hypericaceae and the combined clade in turn sister to Calophyllaceae, as seems probable, I look forward to seeing hypotheses to explain how the dramatic changes in the vegetative body that have made understanding Podostemaceae so problematic for generations of systematists took place. That conventional wisdom has trouble in understanding or explaining how the morphologies of groups like Hypericaceae and Podostemaceae can be related is largely a problem with conventional wisdom.
We used to assume that features like highly scalariform vessel perforation plates or complete absence of vessels, or a flower with an androecium that had many stamens, a superior ovary, or separate petals, were necessarily plesiomorphic or "primitive", and conversely a simple perforation plate and the presence of vessels, an androecium with few stamens, inferior ovary, or petals that were connnate were almost necessarily apomorphic or "advanced" (but c. f. Stebbins 1951). Such assumptions are incorrect (e.g. Soltis et al. 2005b). Carpels may become secondarily free; carpels may fail to close, the seeds then developing outside the confines of the carpel, as in some Aspagaraceae-Nolinoideae, Violaceae, Berberidaceae, Malvaceae-Sterculioideae, etc.; in Peliosanthes teta, perhaps the only species in Peliosanthes (Asparagaceae-Nolinoideae) the ovary varies from superior to inferior (Jessop 1976: species limits here need close investigation; see also Kuzoff et al. 2001 and Soltis & Hufford 2002: Saxifragaceae; Apiales [esp. Pittosporaceae], Asterales [see Menyanthaceae], Poales, etc.); many-seeded carpels can evolve from few-seeded carpels (Razafimandimbison et al. 2008, but c.f. in part Beaulieu & Donoghue 2013); monoecy may be derived from dioecy (Schaefer & Renner 2010 and references). Classic studies such as those by Babcock (e.g. 1947) on Crepis that assumed that evolution - in this case of the karyotype in particular - was unidirectional have needed comprehensive re-evaluation (Enke & Gemeinholzer 2008). Most if not all characters have reversed and/or evolved in parallel, and parallel evolution may occur even at the level of amino acid substitution, as in the independent acquisition of the phosphoenolpyruvate carboxylase (pepC) gene in C4 photosynthesis in grasses (Christin et al. 2007b; see also Bläsing et al. 2000).
Similar problems have affected generic circumscriptions, with results that are similar to those just discussed above for parasitic and wind-pollinated plants, etc. Thus placing too much emphasis on the value of animal pollination syndromes when drawing generic boundaries has all too often led to taxa that are highly unsatisfactory phylogenetically (see e.g. Acanthaceae, Bignoniaceae, Campanulaceae, Ericaceae, Melastomataceae, Orchidaceae, etc.) while over-reliance on characters of fruit and seed (see particularly Brassicaceae and Apiaceae) has also led to unsatisfactory generic limits. Again, the more general problem is the use of one or a very few characters that have been weighted a priori to structure classifications (see also García et al. 2009). Although it is not surprising that such an approach does sometimes result in the delineation of taxa that have indeed turned out to be quite distinct (c. f. e.g. Burtt: Astragalus versus Oxytropis), there are major changes in generic limits underway.
Many families in these pages are polythetic at the morphological level, that is, they lack unique features characterizing ("defining") all and only members of that family. They can be recognised phenetically only by the unique combinations of characters that they possess. This is the result of evolution; the synapomorphy characterizing a lineage may be lost or modified beyond easy recognition in some of its members, or the synapomorphy may appear to be identical to a feature that has evolved in parallel in a quite unrelated plant. That plant groups are polythetic is almost as much a feature of the paraphyletic taxa common in evolutionary classifications as of monophyletic taxa. Nevertheless, many families recognized here now include substantial variation as phenetically distinct derived groups are placed in their proper phylogenetic position - examples are the erstwhile Empetraceae, a wind-pollinated group, now included in Ericaceae, and the various derived, small-flowered aquatic and wind-pollinated groups that are included in the overwhelmingly large-flowered and animal-pollinated Plantaginaceae.
Thus some families as delimited here may not be easy to recognize, but remember that detecting relationships - use whatever characters you can, even if they are not obvious - and naming a plant - focus on obvious characters that may not reflect relationships - are quite different problems. Taxa, although "natural", may not be readily recognizable, indeed, it was in exactly this context that Lamarck worked out the basic principles of writing dichotomous keys in 1778. Of course, Lamarck's idea of nature was very different from ours - there was some kind of continuum of form between living organisms, with no major gaps anywhere - but this meant that his genera (for example) might well not be sharply distinct from each other, even if each was a part of the continuum that was life. Perhaps the best way of identifying plants at the family level is by well-made multiple access keys, as in Watson and Dallwitz (1992a onwards: family limits there may differ substantially from those adopted here). Multiple access keys free users from the constraints of dichotomous keys in which particular characters are needed at each step of the identification process before there can be further progress. Instead, whatever characters are evident on a specimen can be used in whatever order is convenient; when linked to illustrations, glossaries, etc., their power is enormous (see Dallwitz et al. 2000  for the principles underlying their construction and use). Nevertheless, dichotomous keys such as those of Hutchinson (1973), Franz Thonner (Geesink et al. 1981) and Cullen (2006) have their uses, although even in the last-named, despite its date of publication, the family limits accepted do not reflect much in the way of recent findings. Furthermore, as Mary Barkworth (pers. comm.) pointed out, the structuring of information in keys may mean that their users can acquire general knowledge about plants - although of course taxa coming out adjacent in keys may well not be at all related, a fact that is all too frequently forgotten.
(When identifying large numbers of plants, even more efficient than either style of identification, and certainly lots more fun, is sight identification. However, unless one has a photographic memory, one has to build up a good general knowledge of comparative plant morphology, and it is on this the ability to make accurate identifications depends. When faced with an unknown plant, I always look for leaf teeth and stipules, and check leaf insertion; smelling crushed leaves can also be helpful. The short paragraphs added after most families may help in confirming familial identifications. In this context, nodal anatomy can usually be checked using a razor and a hand lens.)
For the record, and for the little that it is worth, there are 4 orders and 13 families of gymnosperms characterised on these pages, and together they include some 82 genera and 947 species. For angiosperms, comparable figures are 57 orders, 449 families, 13,208 genera, and 261,750 species (of which monocots include 11 orders, 89 families, 2,759 genera and 52,760 species). Note, however, that higher mathematics was never my strong point, and anyway these are pretty meaningless figures; even for species, which many (but not all) might concede smacked slightly more of reality than other taxa, estimates range as high as 422,000 (Govaerts 2001; see Joppa et al. 2010 for literature), and perhaps 10-20% more are currently undescribed (Joppa et al. 2010). Furthermore, numbers of genera and species change daily. Nevertheless, as emphasized here, families are useful in teaching, we as a community can ensure that their limits remain largely stable, and by concentrating on relatively few of them one can gain some familiarity with much of the world's flora.
ON FORMING THE CLADE CHARACTERIZATIONS (AND THINKING ABOUT APOMORPHIES)
The organization of the information throughout is hierarchical, that is, character states constant or almost constant in higher groupings are not mentioned at lower levels. This is in line with a phylogeny- or tree-based system, yet it has, perhaps ironically, long been seen as being an advantage of many so-called natural systems, even those that owe nothing to evolutionary ideas (e.g. Cesalpino 1583; Jussieu 1789). However, there is much to do to make this style of presentation fully effective. In particular, whether character states more or less constant in a group are synapomorphies for it often waits for further clarification of relationships both within the group and between that group and its immediate relatives. For example, although most Annonaceae have stamens with distinctive prolongations of the connective, if taxa like Anaxagorea are sister to the rest of the family, such connectives may not be a synapomorphy of Annonaceae, nor may indehiscent fruits and the absence of staminodes (e.g. Scharaschkin & Doyle 2005, 2006); as more is found out about phylogenies, such examples multiply. Similarly, the dismemberment of the Icacinaceae and association of fragments once in that family with Garryales and Aquifoliales in particular (see also the circumscriptions in A.P.G. 2003, c.f. A.P.G. 1998) has important effects on the characterisations of those taxa (c.f. Bremer et al. 2001).
The character hierarchy was built up by first drawing up lengthy descriptions of families and then fitting the characters in the descriptions to molecular-based trees with rather conservative topologies. I began by using the trees presented by A.P.G. (1998), but there continue to be substantial advances in our understanding of relationships, e.g. at the base of the angiosperm tree, within orders such as Ericales, Caryophyllales and Malpighiales, and in families such as the old Icacinaceae, Escalloniaceae and Boraginaceae. A number of these changes are well supported and have been incorporated in A.P.G. II (2003) and III (2009). Elaborations of the phylogeny continue, and they allow the more accurate placing of characters on the tree.
The states of some characters at the base of the angiosperm tree are fairly obvious, hence the fairly lengthy characterisation (apomorphies and plesiomorphies definitely mixed!) for the angiosperms as a whole. For some characters, I have worked up the tree, placing them as high as the evidence suggested. Otherwise, features in common to each clade, whether order, families within an order, or groups of orders, are those that are as far as is known common to all the family characterizations in that clade; they may also be synapomorphies (but see below), and are placed at the lowest level in the tree for which I have information on the variation. For some features I have used both approaches, but confusion should be minimal. As relationships and our knowledge of the variation within characters improve, the top-down and bottom-up approaches merge.
The validity of an approach that fits morphological variation to a molecular tree may rightly be questioned (but see e.g. Doyle & Endress 2011 and earlier papers). However, I think it rather unlikely that branches that are well supported in molecular analyses will be overturned by morphological data. Analysis of morphological data alone does provide support for many of the clades evident in molecule-only analyses, and in conjunction with molecular data may lead to increased support for clades (e.g. Hufford 1992; Nandi et al. 1998: here adding morphological data reduces support for a number of critical clades, too, a not-uncommon phenomenon; Doyle & Endress 2000), however, in none of these papers is the use of morphology without ambiguity. It is unfortunately clear that the use of morphology alone may not suggest problems in the phylogenetic placement of taxa that later turn out to have been wrongly included (e.g. Zhang et al. 1992, but examples are numerous). Thus I have been wary of putting much weight on clades that have only morphological support, yet at the same time I have treated molecule-based clades with low bootstrap or jacknife values support values (esp. below 70%) or posterior probabilies (below 0.95) likewise. Other reasons for prefering to fit morphological variation to a tree are mentioned below.
Morphological and molecular data are very rarely in irreconcilably strong conflict. However, examples that tend in that direction are the relative positions of the Monimiaceae and Hernandiaceae (Laurales), and there have also been arguments about the position of Hanguanaceae (Commelinales [as here, now very likely] or Zingiberales?), and of Triplostegia (is it in Caprifoliaceae-Dipsacacoideae or -Valerianoideae? - see Dipsacoideae). Although trees based on analyses of morphological data alone rarely command much bootstrap support, Weins et al. (2010 and references) is an example of the integration of morphological and molecular data, and fossils and extant organisms. Both amount and quality of data are important, less so proportion, i.e. the ratio of molecular to morphological characters, and of course it is not simply data that matter, but how they are analysed (Morlon et al. 2011). Fossils are unlikely to affect the topologies of the trees presented here, but see below for their importance in understanding morphological evolution.
Indeed, the general congruence between morphological and molecular data is impressive and heartening, and many clades can be characterised morphologically. It seemed in 1998 that there were no unambiguous morphological synapomorphies for angiosperm orders (K. Bremer 2000), and this is still true if by "unambiguous" is meant "non-homoplasious". However, many orders can be characterised, and many of the features in these characterisations will turn out to be synapomorphies (see below), even if homoplasious and morphologically indistinguishable from synapomorphies elsewhere on the tree, at least at the current level of morphological and developmental observation.
Identifying apomorphies is important because understanding the evolution of characters is one of our major goals. For this, several preconditions must be met. One needs to have an accurate, robust phylogeny, one has to have examined the right taxa both from the point of view of morphology and molecules, one has to have coded the characters correctly (i.e., delimited states appropriately), one has to have used the right model of evolution when fitting the variation to the tree, and finally, and little discussed here (but see e.g. the notes on the diversification and evolution of angiosperms), one has to establish the right temporal context and to factor in other relevant aspects of the environment (see e.g. Omland 1999; Stevens 2006b).
On each order page the features associated with each node leading to the order in question are summarised, and other putative synapomorphies for family groups will then be found in the page itself. I have finally (xii.2011) begun to suggest family- (and lower) level synapomorphies. If the distributions of these features are compared with those in individual studies discussing the evolution of such features (e.g. Turgeon et al. 2001; Bremer et al. 2001; Endress 2001; Albach et al. 2001a; Judd et al. 2003; Judd & Olmstead 2004; D. Soltis et al. 2005b; Zhang et al. 2006), differences may be found. Although such studies have been integrated into the characterisations as far as possible, there are five reasons why there may be differences where features are placed on the trees, and these reasons link to the preconditions just mentioned.
- Firstly, I may not have found all the information about a particular character, there may be disagreement over its interpretation (e.g. Austrobaileyales), or I have added unpublished information (e.g. Primulaceae and their relatives, nodal anatomy, etc.; Diapensiaceae, leaf ptyxis; and Peridiscaceae, Centroplacaceae, etc.).
- Secondly, the sampling of nearly all molecular studies is incomplete (see e.g. Salisbury & Kim 2001 for problems caused by sampling). But if the sampling in molecular studies is less than we might wish - although it is fast improving - that of the morphological and chemical characters whose evolution we are interested in understanding is also often very poor. Here much older literature, especially that from ca 1870-1920, is very valuable, since there we can find surveys, sometimes never improved since, of various aspects of plant anatomy and morphology for individual plant groups. So for many anatomical, chemical and embryological characters that are confidently said to characterise families and other groups, we all too often have no idea if those characters are applicable to the whole clade, or just to a subgroup within that clade. Thus Albach et al. (2001a, see also D. Soltis et al. 2005b) assign possession of iridoids to the base of the asterid I + II clades. However, this feature is placed higher up the tree here, partly because of topological uncertainties, but partly because in Lamiales (for example), the first five clades that are successively sister to the remaining Lamiales that are evident in at least some studies either lack iridoids or (most Oleaceae) have iridoids different from those found in the other members of the clade. Similar problems arise when thinking of the evolution of ellagic acid in Ericales (Stevens 2006b).
- Thirdly, I am fitting characters to conservative tree that may have several polytomies. Polychotomies make optimisation of characters, the assigment of character state change to a particular node on the tree, notably difficult (e.g. Madison & Madison 2002). In nearly all studies of the evolution of characters (D. Soltis et al. 2005b is a good example), the distributions of those characters are optimised on more or less fully resolved trees, and the construction of supertrees may yield much more detailed hypotheses of relationships (for literature on supertrees, see e.g. Cotton & Wilkinson 2007, 2008; Buerki et al. 2010d and literature, see also the supermatrix approach). Of course, some nodes on such fully resolved trees and/or supertrees may have little support, and character optimisations on such trees carry correspondingly little conviction.
- Fourthly, exactly how one goes about optimising a character on a tree is critically important. Thus using either parsimony or maximum likelihood, making apparently reasonable suggestions about weighting gains over losses (or vice versa), or more complex assumptions along similar lines, 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), may greatly affect the position of synapomorphies on trees, and hence our ideas of evolution; Sannier et al. (2007) give a good example concerning where on a tree one might peg changes in microsporogenesis in palms (see also Sannier et al. 2009), while Syme and Oakley (2012) note that some methods allow reversals much more easily than others. Pedersen et al. (2007) discuss the sometimes very substantial effect of node support on the posterior probabilities of ancestral character states. Here I use parsimony optimization, not always as explicit as it might be, but I have tried to indicate where there are particularly important uncertainties as to the positions of particular character changes on the tree.
- Fifthly, I have paid quite a lot of attention, although still far too little, to the delimitation of the character "states" that make up all the characterizations (Stevens 2000 for literature; see Important: Warning below). Although fitting the basic variation - not character states - to a tree in principle allows greater flexibility in understanding morphology in the context of local phylogenies (see also Stevens 2000; Endress 2005c, but c.f. Weins et al. 2010 for problems here), we are some way from being able to do this. Many of the states used here are "conventional", that is, they are descriptors of morphological variation that have been used in botanical literature sometimes for well over a century (see below). They are employed in general descriptions of angiosperms, but not only may delimiting states in this broad context be inappropriate, such states may well have arbitrary limits. Although they may seem to communicate "information", whether they are suitable for either phylogenetic analysis or understanding evolution are separate issues. Thus when interpreting the literature - and this site, too - in which character states are optimised on a tree, one should bear in mind all the problems surrounding the delimitation of states (e.g. Stevens 2000, 2006b). Of course, as character states change, so may our ideas of evolution... (e.g., Lamb Frye & Kron 2003; Hibbett 2004).
One particularly serious problem is the use of morphological features that are divided into "types" - in plant architecture these types are called "models", while variation in leaf venation, pollen, ovule, nucellus, female gametophyte, endosperm, embryo and many other organ systems is also described by terms that represent the same approach. These terms are no more than mental constructs that are our attempts to appreciate the variation of many characters simultaneously - and these characters are in fact varying more or less continuously and independently. Unfortunately, this variation effectively gets "lost" when we use these terms. Thus Blackmore et al. (2009) were able to decompose the pollen types used in Asteraceae into no fewer than 52 separate characters (see also Floyd et al. 1999; Floyd & Friedman 2000; Herendeen & Miller 2000; Acosta et al. 2009). But more than this, we tend to think that evolution is a matter of the morphology represented by one of these terms turning into another. Here I find the approach advocated i.a. by Prusinkiewicz and Barbier de Reuille (2010) as they think about plant form - this is the result of the activity of self-organizing proceses of the plant rather than being under immediate genetic control - very helpful as an antidote; throw in processes like heterochrony (Baum & Donoghue 2002), and our appreciation of morphology can change dramatically. Mathews and Kramer (2012) also help us to think about evolution of form and how novelties might develop over the course of evolutionary history.
There are three more related issues that should be mentioned here. First, we often forget that the 0's and 1's of a morphological data matrix in particular are some degrees removed from the actual structures observed on individual specimens, and that all too often there is no clear link between these states and the structures observed; specimens are prepared, observations/measurements made, and then observations are successively abstracted as statements about species and then of more inclusive groups (Stevens 1996). Since there is nothing that has been functioning as a Genbank for morphological data, it is difficult or even impossible to evaluate whether states have been delimited satisfactorily for any particular study; one can argue that often in phylogenetic studies - as in much of taxonomy as a whole - there are few data in the sense of observations that can be linked to specimens.
Secondly, understanding even current literature can be difficult because terms have no fixed definitions - the term "panicle" can be understood only if one knows how the author of the publication in which you find the term was using it. As Rickett (1954: 2, emphasis in original) noted, "To be uncertain whether "glabrous" means "free from hairs and roughness" or only "free from hairs" is as bad as if p [pi] should stand sometimes for the ratio of a circle to its diameter and sometimes for somthing else; or as if Cu meant sometimes "copper" and sometimes "brass". Yet this is the state of affairs in botany today". Over a half century later, this is still the state of affairs. In this context, an ontology that is generally accepted by botanists is essential (see also Vogt et al. 2010), but see the Plant Ontology Consortium. This ontology will have to deal with the innumerable parallelisms in plants, and again, we have to remember the fact that it is we who have made the terms...
Thirdly, it is an unfortunate fact, but perhaps to be expected, that the delimitation of states and characters does not necessarily become easier with increasing knowledge of development, etc. Thus Buzgo et al. (2004) and Matthews and Endress (2005) show how hard it can be to distinguish between e.g. prophylls and other floral structures, while Penet et al. (2005) find that not all monosulcate pollen in monocots has the same developmental pathway, and suggest that therefore such pollen may not have the same ancestral state. I use Remane's three main criteria of "homology", special properties, position, and intermediates, when determining the basic similarity of structures on different organisms (see Remane 1952; Kaplan 1997: 1 ch. 1; c.f. Endress 2011c, p. 122 - "too limited"). Even these criteria may not yield an unambiguous answer as to what a structure "is", even given a solid phylogeny to provide context for the interpretation of morphology and an improved understanding of development. As Endress (2005c) observed, a number of features - position, function, development, shape, anatomy, histology, gene activity, and relationships to other taxa that clearly have petals - can be used to distinguish a petal (for example) from other floral structures; if a petal does not have one of these features, is it thereby not a petal? For instance, Maturen et al. (2005) found that floral organ diversity genes (B and C) were expressed in the large, white inflorescence bracts of Cornus (see also Costa et al. 2005), while A-class genes can be expressed in the inflorescence, or even in leaves (Champagne et al. 2007: leaf levelopment in Fabaceae-Faboideae [the inverted repeat loss clade]; Prenner et al. 2011: Euphorbia and Asteraceae). There are all intermediates between vessels and tracheids (Schneider & Carlquist 2009; Carlquist & Schneider 2010; Carlquist 2012a), between fully superior and fully inferior ovaries (e.g. Soltis & Hufford 2002), floral phyllotaxis may be very labile, especially in magnoliids and members of the ANITA grade (Staedler & Endress 2009), leaves are not always easily distinguishable from other structures (Rutishauser 1999) - and on it goes.
The take-home message is: Do not be overawed by botanical terms, we made them, not "nature". For me, seeing a plant is forgetting the names its parts are called (with apologies to Weschler 2009); botanical terms are flags that there is variation out there, but little more. As Hesse et al. (2009b: p. 27) observed, "Nature itself neither needs categories nor has any knowledge of categories".
To summarise, given our current understandings of both phylogenies and morphology, evolution of some characters in which we are interested seems very labile (see e.g. D. Soltis et al. 2005b), and I have been cautious when talking about character evolution. Much basic - and unfortunately perhaps unfashionable - work must be carried to clarify the distribution of morphological, anatomical and chemical characters; for excellent examples of what can to be done, see e.g. the work of P. K. Endress and collaborators, P. Leins and C. Erbar, and L.-P. Ronse de Craene and collaborators (floral morphology and development) and S. R. Jensen and collaborators (iridoids). Indeed, acquiring original information about nodal anatomy, cell and tissue distribution, stomatal morphology, seed coat anatomy, and the like is not difficult at all and should be generally encouraged.
There are six final points to remember about the characterisations here, and descriptions in general:
1. I have been much more generally comparative in the ultimate characterisations than is perhaps strictly necessary. That is, the user will be able to find information on the variation of most characters mentioned in the character list as it occurs in all families. An example is leaf ptyxis, which seems to characterise only a few or the terminal groups recognised here, although I have tried to include information about it more generally.
2. More conventional descriptions of a family, for example, as in Cronquist (1981), include a mixture of plesiomorphies and apomorphies at various levels, including apomorphies of groups of genera, or even individual genera, within the family. Although it is difficult to disentangle the importance of the features listed (but typographic conventions, as in Judd et al. 2002, help in part), they better convey a description of the organism as a whole. Nevertheless, by summarizing the relevant part of the character state hierarchy before each ordinal characterization, I perhaps give something of the same effect.
3. Some of the features in the characterisations simply describe the extent of variation within the clade, e.g., "stomata anomocytic or paracytic". This is particularly common when relationships within a family, or between a family and its immediate relatives, are unclear. It is unlikely that features so described will often turn out to be synapomorphies, although elements of the variation they encompass may.
4. A negative feature of the hierarchical approach, at least as presented here, may seem to be the absence of "biology" - all the reader seems to see is lists of characters. In this context, I am reminded of Stebbins's remarks in his review of Cronquist (1981) which read in its entirety "The only material of even peripheral interest to the general evolutionist consists of short commentaries on family relationships placed at the end of the description [sic] of many of the families" (Stebbins 1982, p. 628). However, we know little about the functional or adaptive significance of many synapomorphies. Apart from some wind-pollinated taxa, aquatics and parasites, it is usually difficult to characterise larger groups ecologically, although clades like Ericaceae are exceptions. Indeed, much of the "biology" in more conventional descriptions comes from mention of the pollination biology or other aspects of the biology of particular genera and other small groups within a family, and users will add this emphasis as they focus on the taxa that grow locally. However, I have been adding details of ecophysiology, divergence and/or diversification of clades, particularly striking associations with particular groups of herbivores, fungi, or pollinators, etc., in successive versions of this site.
5. As we find out more about variation we find fewer and fewer features constant throughout a group. Most unqualified statements of presence and absence should properly be qualified as "usually present" or "usually absent" if one is thinking of the characterisations as encompassing the total variation within a clade. Thus Pistia, alone among monocots as so far known, has sieve tube plastids with starch grains, not protein crystals, although the latter is an apomorphy for monocots. Most, if not all, characters that are high-level apomorphies reverse and/or occur in parallel several times on the tree.
6. Hardly surprisingly, fossils in a number of cases suggest character combinations unknown in extant taxa, as may be seen in the discussions of Fagaceae, Platanaceae, Iteaceae, Calycanthaceae, etc. How this will affect characters at interior nodes remains to be seen, but note that there may be questions as to where exactly on the tree a particular fossil is to be placed (e.g., see Nymphaeaceae, Calycanthaceae, Paracryphiaceae, Archaefructus, etc.).
The bottom line is that much effort must continue to be spent in summarizing characters of well-established clades at all levels, providing features by which they may be recognized, and signaling synapomorphies. Remember that (1) our basic morphological, anatomical and chemical knowledge of many critical taxa is woefully incomplete; (2) different assumptions about character evolution may greatly affect the position of synapomorphies on trees; (3) in many cases relationships within and between many groups are too uncertain at present to worry overmuch about synapomorphies; and (4), we must be clear about what we do and do not not know. Nevertheless, it is a relatively easy matter to update notes such as these, and it can be a simple matter to incorporate new data on characters that have never before been considered in the context of a tree.
SUMMARY OF THE SYSTEM
Below is a summary of the relationships within orders of all the families of seed plants. There are a few families that are not recognised, even as options, in A.P.G. III (2009). The families recognised in the most recent edition of Mabberley's The Plant Book (Mabberley 2008) are also largely, but not entirely, consistent with those below. Boraginales have recently (xi.2013) been added. However, all differences are trivial and will - I hope - eventually disappear. Families and orders are directly linked to the main pages where their characterizations appear.
Square brackets - [...] - enclose clades; the plus sign - + - designates terminal sister taxa; a comma - , - denotes part of a polytomy.
[Cycadaceae + Zamiaceae]
[Pinaceae [[Araucariaceae + Podocarpaceae] [Sciadopityaceae [Taxaceae + Cupressaceae]]]]
[Ephedraceae [Gnetaceae + Welwitschiaceae]] ?In Pinales.
Evolution and diversification of the angiosperms
[Hydatellaceae [Cabombaceae + Nymphaeaceae]]Austrobaileyales
[Austrobaileyaceae [Trimeniaceae + Schisandraceae]][Chloranthales + Magnoliids
[Myristicaceae [Magnoliaceae [[Himantandraceae + Degeneriaceae] [Eupomatiaceae + Annonaceae]]]]
[Calycanthaceae [[Siparunaceae [Gomortegaceae + Atherospermataceae]] [Monimiaceae [Hernandiaceae + Lauraceae]]]]Canellales
[Canellaceae + Winteraceae]
[Aristolochiaceae [Piperaceae + Saururaceae]]
[Araceae [Tofieldiaceae [[Alismataceae [Hydrocharitaceae + Butomaceae]] [Scheuchzeriaceae [Aponogetonaceae [Juncaginaceae [Maundiaceae [[Posidoniaceae [Ruppiaceae + Cymodoceaceae]] [Zosteraceae + Potamogetonaceae]]]]]]]]]Petrosaviales
[Nartheciaceae [[Taccaceae + Thismiaceae (limits?)] [Burmanniaceae + Dioscoreaceae]]]
[Velloziaceae, Triuridaceae, Stemonaceae, [Pandanaceae + Cyclanthaceae]]Liliales
[Corsiaceae [Campynemataceae [Petermanniaceae, [Colchicaceae + Alstroemeriaceae], Melanthiaceae, [[Philesiaceae + Rhipogonaceae] [Smilacaceae + Liliaceae]]]]Asparagales
[Orchidaceae [[Boryaceae [Blandfordiaceae [Lanariaceae [Asteliaceae + Hypoxidaceae]]]] [[Ixioliriaceae + Tecophilaeaceae] [Doryanthaceae [Iridaceae [Xeronemataceae [Xanthorrhoeaceae [Amaryllidaceae + Asparagaceae]]]]]]]]
[[Typhaceae + Bromeliaceae] [Rapateaceae [[Mayacaceae [Eriocaulaceae + Xyridaceae]] [Thurniaceae [Juncaceae + Cyperaceae]]] [Anarthriaceae + Restionaceae]] [Ecdeiocoleaceae + Poaceae [Flagellariaceae + Joinvilleaceae]]]]]]]]Commelinales
[[Commelinaceae + Hanguanaceae] [Philydraceae [Haemodoraceae + Pontederiaceae]]]
[Musaceae, [Strelitziaceae + Lowiaceae], Heliconiaceae, [[Cannaceae + Marantaceae] [Costaceae +Zingiberaceae]]]
[Eupteleaceae [Papaveraceae [[Lardizabalaceae + Circaeasteraceae] [Menispermaceae [Berberidaceae + Ranunculaceae]]]]]Proteales
[Sabiaceae [Nelumbonaceae [Platanaceae + Proteaceae]]]Trochodendrales
[Didymelaceae + Buxaceae]
[Gunneraceae + Myrothamnaceae]
[Peridiscaceae [[Paeoniaceae [Altingiaceae [Hamamelidaceae [Cercidiphyllaceae + Daphniphyllaceae]]]] [[Crassulaceae [Aphanopetalaceae [Tetracarpaeaceae [Penthoraceae + Haloragaceae]]]] [Iteaceae [Grossulariaceae + Saxifragaceae]]]]], Cynomoriaceae unplacedVitales
[Krameriaceae + Zygophyllaceae]
[Lepidobotryaceae + Celastraceae]
[Huaceae [[Connaraceae + Oxalidaceae] [Cunoniaceae [Elaeocarpaceae [Brunelliaceae + Cephalotaceae]]]]]
[[Ctenolophonaceae [Erythroxylaceae + Rhizophoraceae]], Irvingiaceae, Pandaceae, [Ochnaceae [[Bonnetiaceae + Clusiaceae] [Calophyllaceae [Hypericaceae + Podostemaceae]]]]] [[[Lophopyxidaceae, Putranjivaceae], Caryocaraceae, Centroplacaceae, [Elatinaceae + Malpighiaceae], [Balanopaceae [[Trigoniaceae + Dichapetalaceae] [Chrysobalanaceae + Euphroniaceae]]]] [[Humiriaceae [[Achariaceae [Goupiaceae + Violaceae] [Passifloraceae [Lacistemataceae + Salicaceae]]]]] [[Peraceae [Rafflesiaceae + Euphorbiaceae]] [[Phyllanthaceae + Picrodendraceae] [Linaceae + Ixonanthaceae]]]]]
[Quillajaceae [Fabaceae [Polygalaceae + Surianaceae]]]
[Rosaceae [[Rhamnaceae [Elaeagnaceae [Barbeyaceae + Dirachmaceae]]] [Ulmaceae [Cannabaceae [Moraceae + Urticaceae]]]]]
[Anisophylleaceae [[Corynocarpaceae + Coriariaceae] [Cucurbitaceae [Tetramelaceae [Datiscaceae + Begoniaceae]]]], Apodanthaceae unplaced
[Nothofagaceae [Fagaceae [[Myricaceae + Juglandaceae] [Casuarinaceae [Ticodendraceae + Betulaceae]]]]]
[Geraniaceae [Melianthaceae [Vivianaceae [Greyiaceae + Francoaceae]]]]
[Combretaceae [[Onagraceae + Lythraceae] [[Vochysiaceae + Myrtaceae] [Melastomataceae [Crypteroniaceae [Alzateaceae + Penaeaceae]]]]]]
[[Staphyleaceae [Guamatelaceae [Crossosomataceae + Stachyuraceae]]] [Aphloiaceae [Geissolomataceae + Strasburgeriaceae]]]
[Biebersteiniaceae, Nitrariaceae, [[Kirkiaceae [Anacardiaceae + Burseraceae]] [Sapindaceae [Simaroubaceae, Rutaceae, Meliaceae]]]]Huerteales
[[Gerrardinaceae + Petenaeaceae] [Tapisciaceae + Dipentodontaceae]]Malvales
[Neuradaceae [Thymelaeaceae [Sphaerosepalaceae, Bixaceae, [Cistaceae [Sarcolaenaceae + Dipterocarpaceae]], [Cytinaceae + Muntingiaceae], Malvaceae]]]Brassicales
[[Akaniaceae + Tropaeolaceae] [[Moringaceae + Caricaceae] Setchellanthaceae[ [Limnanthaceae [Koeberliniaceae[ [Bataceae + Salvadoraceae]] [Emblingiaceae [[Pentadiplandraceae [Borthwickiaceae [Gyrostemonaceae, Resedaceae, Stixis and relatives]]] Tovariaceae [Capparaceae [Cleomaceae + Brassicaceae]]]]]]]]]]Berberidopsidales
[Aextoxicaceae + Berberidopsidaceae]
[Erythropalaceae [Strombosiaceae [Coulaceae [Ximeniaceae, Aptandraceae, Olacaceae [Octonemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]]]]], Balanophoraceae unplaced
[[[Droseraceae [Nepenthaceae [Drosophyllaceae [Ancistrocladaceae + Dioncophylleaceae]]]] [[Frankeniaceae + Tamaricaceae] [Polygonaceae + Plumbaginaceae]]] [Rhabdodendraceae [Simmondsiaceae [[Asteropeiaceae + Physenaceae] [Macarthuria [Microteaceae [[Caryophyllaceae [Achatocarpaceae + Amaranthaceae]] [Stegnospermataceae [Limeaceae [[Lophiocarpaceae [Hypertelis [Barbeuiaceae [Aizoaceae [Gisekiaceae [[Sarcobataceae + Phytolaccaceae] [Rivinaceae + Nyctaginaceae]]]]]]] [Molluginaceae [Montiaceae [[Halophytaceae [Didiereaceae + Basellaceae]] [Talinaceae [Anacampserotaceae [Portulacaceae + Cactaceae]]]]]]]]]]]]]]]]
[[Cornaceae [Grubbiaceae + Curtisiaceae]] [Nyssaceae [Hydrostachyaceae [Hydrangeaceae + Loasaceae]]]]Ericales
[[Balsaminaceae [Marcgraviaceae + Tetrameristaceae]] [[Polemoniaceae + Fouquieraceae], Lecythidaceae, [[Sladeniaceae + Pentaphylacaceae], [Sapotaceae [Ebenaceae + Primulaceae]], [Mitrastemonaceae, Theaceae, [Symplocaceae [Styracaceae + Diapensiaceae]], [[Sarraceniaceae [Roridulaceae + Actinidiaceae]] [Clethraceae [Cyrillaceae + Ericaceae]]]]]]]
[Metteniusaceae, Oncothecaceae], Icacinaceae, and some unplaced ex-IcacinaceaeGarryales
[Garryaceae + Eucommiaceae]
[Rubiaceae [[Loganiaceae + Gelsemiaceae] [Gentianaceae + Apocynaceae]]]Unplaced (?sister to Solanales)
[[Montiniaceae [Sphenocleaceae + Hydroleaceae]] [Convolvulaceae + Solanaceae]]
[[Codonaceae [Wellstediaceae + Boraginaceae]] [Hydrophyllaceae, Nama, etc. [Heliotropiaceae [Cordiaceae + Ehretaceae]]]
[Plocospermataceae [[Carlemanniaceae + Oleaceae] [Tetrachondraceae [[Peltanthera [Calceolariaceae + Gesneriaceae]] [Plantaginaceae [Scrophulariaceae [Stilbaceae [[Byblidaceae + Linderniaceae] [[Lamiaceae [Mazaceae [Phrymaceae [Paulowniaceae + Orobanchaceae]]]] [Thomandersiaceae + Verbenaceae], Pedaliaceae, [Schlegeliaceae + Martyniaceae] Bignoniaceae, Acanthaceae, Lentibulariaceae]]]]]]
[[Cardiopteridaceae + Stemonuraceae] [Aquifoliaceae [Helwingiaceae + Phyllonomaceae]]]
[[Rousseaceae + Campanulaceae] [Pentaphragmataceae [[Alseuosmiaceae [Phellinaceae + Argophyllaceae]] [Stylidiaceae [Menyanthaceae [Goodeniaceae [Calyceraceae + Asteraceae]]]]]]]Escalloniales
[Bruniaceae + Columelliaceae]
[Pennantiaceae (position?) [Torricelliaceae [Griseliniaceae [Pittosporaceae [Araliaceae [Myodocarpaceae + Apiaceae]]]]]]
[Adoxaceae + Caprifoliaceae]
ON POORLY-KNOWN TAXA THAT ARE IN URGENT NEED OF STUDY
There are several areas where more phylogenetic study is needed, since our current (lack of) ideas of phylogenetic relationships there precludes our thinking about evolution. These include Icacinaceae, Oncothecaceae, Metteniusaceae and a number of unplaced ex-Icacinaceous genera. All these are probably somewhere basal in the asterid I/lamiid clade, but whether they are to be included in Garryales is unknown; the topology of the tree around here could considerably affect our understanding of asterid I + II evolution. Core Caryophyllales - the clade with betalain-including taxa - need attention; not only are some nodes still poorly supported, but Phytolaccaceae and the Amarathaceae-Chenopodiaceae areas need particular attention. Phytolaccaceae are probably paraphyletic, and Microtea, which used to be in the family, may even be sister to the rest of Core Caryophyllales (Schaferhoff et al. 2009). Our understanding of relationships in much of Lamiales and Malpighiales is improving, although there is still more to do there. The positions of Dilleniaceae, Vitaceae and Berberidopsidaceae in particular are not fixed, although they will probably be towards the bottom of speciose clades.
Although a vast amount of morphological s.l. information is being developed from question-driven research on model organisms like Zea, Arabidopsis, Antirrhinum, and a few others, it is often difficult to know how far the results can be extrapolated. Indeed, four things have long impressed (or depressed) me about the state of general botanical knowledge.
1. How little we really know when we discuss evolution - for most features, we extrapolate from a miniuscule data base.
2. How little morphological s.l. knowledge is added in most phylogenetic studies (but see below).
3. How much we are dependent on general surveys from the 1880s to the 1930s in particular (for character systems like cytology and plant chemistry the surveys are later, but even here our knowledge base is currently increasing very slowly), although for aspects of floral development a few authors have indeed added substantial amounts of data over the last thirty years.
4. How easy it is to add information about many organ systems.
A more comprehensive understanding of morphology is urgently needed to enable broad evolutionary questions to be answered with a greater degree of confidence, and there is a particular need for targeted surveys of the morphological variation of particular groups. Indeed, given the limits of time and resources, one can profitably focus on small clades an understanding of the morphology of which will have the greatest effect on character reconstructions. In the case of a focus on the inner nodes of the tree, these will be along the spines of the branches, small clades sister to the rest of a very speciose clade, etc. Add to that a judicious sampling of the morphology of these more speciose clades, a preliminary understanding of the basic patterns of evolution should be attainable. Our current basic morphological knowledge is far less extensive than we would like it to be. The bottom line is that neither phylogeny without good comparative morphological knowledge nor comparative morphology without a good phylogeny is of much use.
To help in building up a more extensive information base that will facilitate our thinking about the larger patterns of flowering plant evolution, the list below includes a number of quite small taxa whose phylogenetic position is such that information on embryo sac development, chemistry, seed anatomy, etc., is particularly important for our understanding of the evolution of those features. This is not to say that broad surveys within speciose clades are not needed - they are desperately needed (see also Endress 2011) - but the taxa listed are small and so reasonable subjects for targeted comprehensive studies. Many of the taxa listed may be suitable for study by Masters students. Of course, given the current academic climate, I cannot say that such studies will be highly regarded by tenure and promotion committees (bless their hearts, wherever they might be), but they should nevertheless be integral to all phylogenetic studies that are concerned with character evolution and integral parts of grant proposals.
For the broader studies that are also needed, sampling should be carefully targeted in the context of a phylogeny of the group of interest; untargeted surveys, or surveys of groups whose phylogeny is unclear, may yield less of interest than one might hope (c. f. Schönenberger & von Balthazar 2006).
The taxa listed below come from all over the world except the northern Temperate and Arctic zones. Tropical Africa (even excluding the Cape region and Madagascar), Central and tropical South America, and Australia-New Zealand are particularly well represented, East Asia and Indo-Malesia somewhat less so, then the Cape region, Madagascar, and the southern U.S.A./northern Mexico, and finally New Caledonia, temperate South America, and Europe. Although some of these genera like Triceratella (Commelinaceae) are very rare, others are quite common, or are even in cultivation (Rehmannia, Aextoxicon, Portulaca, etc.). Such a list does not pretend to be exhaustive, indeed, there are some genera that are quite well known, but for which important information is lacking - thus I know of no reports of fertilization from Nothofagus (Nothofagaceae, sister to rest of Fagales). Given our general level of knowledge, there is no shortage of plants for us to look at.
In addition to the taxa listed, many others, especially in Geraniales, practically the whole of Phytolaccaceae and Molluginaceae, Irvingiaceae, Kirkiaceae, Acanthaceae-Nelsonioideae, Escalloniaceae, Bruniaceae, etc., could well have been included. Most holoparasites need developmental and embryological studies, although these taxa are likely to be highly autapomorphic. Furthermore, as phylogenies in Lamiales, Caryophyllales, etc., become better resolved, other clades in urgent need of study will become apparent.
The primary literature should be consulted to see exactly what is known about the individual taxa on the list (the volumes edited by Kubitzki et al. (1993 onwards) are a beginning; for floral morphology in particular, see Ronse de Craene (2010), Leins and Erbar (2010), Endress (2010), Rudall (2010) and the references there. Charcater surveys will also be useful. Although one might like to know all characters for all taxa (a very incomplete list of characters could be generated from the Characters page), in different groups different features will seem more important. Thus in Brasicales, more information about root trichoblasts would be valuable, although the significance of this feature, like so many others, is unknown.
Finally, authors are encouraged to make sure their basic observations are placed in databases like DRYAD that are in the public domain (Rauscher et al. 2010); however, remember that character states with 0s and 1s are often not sufficient (Stevens 1996, 2000) since as data are added or the question is changed the circumscription of states may need to be adjusted.
Note that mention of “basal” in the comments below is relative. It means basal in a tree relative to other more speciose clades; there are no implications that members of such clades are “primitive” or plesiomorphic.
Achatocarpaceae: Caryophyllales - sister to Amaranthaceae s.l. Achatocarpus (Mexico to Argentina) Phaulothamnus (S.W. U.S.A., N. Mexico): 10 and 1 spp. respectively.
Aextoxicaceae: one of two families in Berberidopsidales, along spine below the asterids, see also Berberidopsidaceae. Aextoxicon (Chile): 1 sp.
Akaniaceae: Brassicales - sister to all other Brassicales. Akania (E. Australia), Bretschneidera (S.E. Asia): 1 and 1 spp. respectively.
Alseuosmiaceae: member of small clade in Asterales. Alseuosmia (New Zealand), Crispiloba (N.E. Australia), Periomphale (New Caledonia), Platyspermation (New Caledonia), Wittsteinia (S.E. Australia, New Guinea): 5, 1, 1, 1, and 2 spp. respectively.
Anacampserotaceae: Caryophyllales - sister to Cactaceae. Anacampseros +? (Africa, S.W. U.S.A., Central and South America, Australia, very scattered): 32 spp. in whole clade.
Aphanopetalaceae: Saxifragales. Aphanopetalum (W. and E. Australia): 2 spp.
Aphloiaceae: Crossosomatales - sister to rest of one major clade in the order. Aphloia (E. Africa, Madagascar, Seychelles): 1-several spp.
Asteraceae: Asterales. Corymbium (South Africa); 7 spp. Sister to Asteroideae.
Asteropeiaceae - one family of two in clade sister to core Caryophyllales (see also Physenaceae). Asteropeia (Madagascar): 8 spp.
Barbeuiaceae: base of spine of major clade in core Caryophyllales. Barbeiua (Madagascar): 1 sp.
Barbeyaceae: Rosales, near Rhamnaceae. Barbeya (Horn of Africa, Arabia): 1 sp.
Berberidopsidaceae - one of two families in Berberidopsidales, along spine below the asterids (see also Aextoxicaceae). Berberidopsis (Chile, E. Australia), Streptothamnus (E. Australia): 2 (florally very different) and 1 spp. respectively.
Biebersteiniaceae: Sapindales, perhaps sister to rest of order. Biebersteinia (Greece to C. Asia): 5 spp.
Bixaceae: Malvales, isolated in Bixaceae. Diegodendron (Madagascar): 1 sp.
Boraginaceae s.l. Codon (South Africa), Wellstedia (N.E. Africa, South West Africa): 2 and 6 spp. respectively. Successively sister to Boraginaceae.
Borthwickiaceae - core Brassicales. Borthwickia (S.W. Yunnan, China, and adjacent Burma): 1 sp.
Brassicaceae: Brassicales. Aethionema (Mediterranean to Afghanistan): 70 spp. Sister to all other Brassicaceae.
Carlemanniaceae: Lamiales - small clade sister to Oleaceae, together near basal in order. Carlemannia, Silvianthus (both S.E. Asia to W. Malesia): 3 and 1 spp. respectively.
Campanulaceae: Asterales - basal or near in the family. Cyphioideae: Cyphia (Africa): 60 spp. Cyphocarpoideae: Cyphocarpus (Chile): 2 spp. Nemacladoideae: Nemocladus (S.W. North America): 12 spp.
Campynemataceae: Liliales. Campynema (Tasmania), Campynemanthe (New Caledonia, somewhat known): 1 and 3 spp. respectively.
Caryocaraceae - unplaced in Malpighiales. Anthodiscus (tropical South America), Caryocar (Central America, tropical South America): 8 and 15 spp. respectively.
Centroplacaceae: isolated in Malpighiales. Centroplacus (West Africa), Bhesa (Indomalesia): 1 and 5 spp. respectively.
Codonaceae: see Boraginaceae.
Combretaceae: Myrtales. Strephonema (West Africa): 3 spp. Sister to rest of family.
Commelinaceae: Commelinales. Cartonema (N. and S.W. Australia, New Guinea) and probably Triceratella (Zimbabwe): 11 and 1 spp. respectively. Sister to rest of family.
Convolvulaceae: Solanales. Humbertia (Madagascar): 1 sp. Sister to rest of family.
Cordiaceae: Boraginales. Hoplestigma (West Africa). 1 spp. Strange floral morphology.
Ctenolophonaceaee: Malpighiales - unplaced. Ctenolophon (tropical West Africa, Malesia): 3 spp.
Curtisiaceae: Cornales. Curtisia (Southern Africa): 1 sp.
Cyrillaceae: Ericales, sister to Ericaceae. Cliftonia (S.E. U.S.A), Cyrilla (S. U.S.A. to N. South America): 1 and 1 spp. respectively.
Dasypogonaceae - unplaced commelinid. Baxteria (S.W. Australia), Calectasia (S.E. Australia), Dasypogon (S.W. Australia), Kingia (S.W. Australia): 1, 11, 3, and 1 spp. respectively.
Didymelaceae: Buxales, sister to (or in) Buxaceae. Didmyeles (Madagascar): 2 spp.
Dipentodontaceae - in poorly known Huerteales. Dipentodon (E. Asia), Perrottetia (Central and W. South America, S.E. Asia to Australia): 1 and 15 spp. respectively.
Dirachmaceae: Rosales - near Rhamnaceae. Dirachma (Horn of Africa): 2 spp.
Emblingiaceae - spine of core Brassicales. Emblingia (S.W. Australia): 1 sp.
Euphroniaceae: Malpighiales. Euphronia (N. South America): 3 spp.
Fabaceae: Fabales. Near basal in family - Duparquetia (tropical West Africa): 1 sp.
Geissolomataceae: Crossosomatales. Geissoloma (South Africa): 1 sp.
Gelsemiaceae: Gentianales - ?sister to Apocynaceae. Pteleocarpa (W. Malesia); 1 species, distinctly odd.
Geraniaceae: Geraniales. Hypseocharis (Andean South America): 1-3 spp. Sister to rest of family
Gerrardinaceae - in poorly known Huerteales. Gerrardina (S. and E. Africa): 2 spp.; they look rather different.
Giseckiaceae: core Caryophyllales. Giseckia (Africa to E. Asia): 5 spp.
Goupiaceae: Malpighiales, ?sister to Violaceae. Goupia (Central and N.E. South America): 2 spp.
Griseliniaceae: backbone of Apiales. Griselinia (New Zealand and S. South America): 6 spp.
Grubbiaceae: Cornales, very small clade. Grubbia (South Africa, the Cape): 3 sp.
Guamatelaceae: Crossosomatales. Guamatela (Guatemala): 1 sp.
Helwingiaceae: Aquifoliales. Helwingia (Himalayas to Japan): 3 spp.
Huaceae - perhaps sister to rest of Oxalidales. Afrostyrax, Hua (both tropical W. Africa): 1 and 2 spp. respectively.
Hypertelis - near Aizoaceae, core Caryophyllales. Hypertelis (Africa, Saint Helena): 8 spp.
Icacinaceae, perhaps close to Garryales, Metteniusaceae, Oncothecaceae, are poorly known. There is also a group of genera once included in Icacinaceae and still perhaps to be placed near them, includes Apodytes (Old World tropics, 15 spp.), Calatola (Mexico to Ecuador, 7 spp.), Dendrobangia (tropical South America, 2 spp.), Emmotum (tropical South America, 12 spp.), Cassinopsis (Africa, Madagascar, 6 spp.), Platea (Malesia, 5 spp.), Rhaphiostylis (tropical W. Africa, 6 spp.).
Lacistemataceae: Malpighiales, sister to Salicaceae. Lacistema, Lozania (both Central and South America): 11 and 3 spp. respectively.
Leycthidaceae: Ericales. Foetidioideae, sister to Planchonioideae - Foetidia (centred on Madagascar): 17 spp. Napoleonoideae, sister to rest of family - Crateranthus, Napoleona (both tropical West Africa): 3 and 8 spp. respectively.
Lepidobotryaceae: Celastrales - sister to Celastraceae. Lepidobotrys (tropical W. Africa), Ruptiliocarpon (C. America, W. South America): 1 and 1 spp. respectively.
Limeaceae: Caryophyllales - clade along spine of core Caryophyllales. Limeum (Africa to Pakistan, esp. South Africa), Macarthuria (S.E./S.W. Australia); 26 and 10 spp. respectively.
Lophiocarpaceae - base of spine of major clade in core Caryophyllales. Lophiocarpus (South Africa), Corbichonia (Africa to Asia): 4 and 2 spp. respectively.
Lophopyxidaceae: Malpighiales - sister to Putranjivaceae, small unplaced clade. Lophopyxis (Malesia to W. Pacific): 1 sp.
Macarthuria - ?sister to all other core Caryophyllales. Macarthuria (Australia, the periphery): 10 spp.
Mayacaceae - critical clade in Poales. Mayaca (West Africa, tropical America): 4 spp.
Metteniusaceae, unplaced - near Icacinaceae, Garryales, Oncothecaceae, etc. Metteniusa (Costa Rica to NW South America): 7 spp.
Microteaceae - ?sister to all other core Caryophyllales. Microtea (Central and South America, Antilles): 9 spp.
Montiniaceae: Solanales - rather basal in order. Grevea (E. Africa, Madagascar), Kaliphora (Madagascar), Montinia (S. Africa): 3, 1, and 1 spp. respectively.
Muntingiaceae: Malvales. Dicraspidia (Central to N.W. South America), Muntingia (tropical America, somewhat known): 1 and 1 sp. respectively. Neotessmannia (Peru): 1 sp. Does this belong?
Neuradaceae - ?sister to all other Malvales. Grielium (South Africa), Neurada (E. Mediterranean to India), Neuradopsis (S.W. Africa): 5, 1 and 3 spp. respectively.
Nitrariaceae: Sapindales, near basal. Nitraria (Mediterranean to C. Asia, S. North America), Peganum, Tetradiclis (both E. Europe to C. Asia): 12, 6 and 1 spp. respectively.
Oncothecaceae: unplaced, near Metteniusaceae, Icacinaceae, Garryales, etc. Oncotheca (New Caledonia): 2 spp.
Orobanchaceae: Lamiales. Rehmannia (East Asia), Trianeophora (EastAsia): 6 and 3 spp. respectively. Sister to rest of family.
Paracryphiaceae: Paracryphiales - sister to Apiales. Paracryphia (New Caledonia), Quintinia (Philippines to New Zealand), Sphenostemon (Celebes to N.E. Australia and New Caledonia); 1, 25, and 10 spp. respectively.
Pennantiaceae: sister to all other Apiales. Pennantia (E. Australia to New Zealand): 4 spp.
Pentadiplandraceae, spine of core Brassicales. Pentadiplandra (tropical W. Africa): 1 sp.
Pentaphragmataceae: Asterales, sister to major clade in order. Pentaphragma (S.E. Asia-Malesia): 30 spp.
Peridiscaceae - probably sister to all other Saxifragales. Medusandra, Soyauxia (both tropical W. Africa), Peridiscus (Amazonia), Whittonia (N. South America): 2, 7, 1, and 1 spp. respectively.
Petenaeaceae - in poorly known Huerteales. Petenaea (C. America): 1 sp.
Phellinaceae, small clade in Asterales. Phelline (New Caledonia): 12 spp.
Phyllonomaceae: Aquifoliales. Phyllonoma (Mexico to W. South America): 4 spp.
Picramniaceae: only member of order. Alvaradoa (Florida, Central America, Bahama, esp. the Greater Antilles, Bolivia to Argentina), Nothotalisia (Panama and N.W. South America), Picramnia (Florida, Central and South America): 5, 3, and 41 spp. respectively.
Poaceae: Poales - clades along basal spine of family. Pharoideae: Leptaspis (Old World tropics), Pharus (New World, Florida to Argentina): 4 and 8 spp. respectively. Puelioideae: Guaduella, Puelia (both tropical W. Africa): 6 and 5 spp. respectively.
Physenaceae, one family of two in clade sister to core Caryophyllales (see also Asteropeiaceae). Physena (Madagascar): 2 spp.
Picramniaceae: Picramniales, along spine of malvids. Alvaradoa (S.E. U.S.A. to Argentina, scattered), Picramnia (S.E. U.S.A. to Argentina): 5 and ca 40 spp. respectively.
Plocospermataceae - sister to all other Lamiales. Plocospermum (Central America): 1 sp.
Picrodendraceae: Malpighiales. Podocalyx (Amazonian South America): 1 sp. Sister to rest of family.
Portulacaceae: Caryophyllales - once removed from sister to Cactaceae. Portulaca (pan(sub)tropical): 40-100 spp.
Primulaceae: Ericales. Maesa (Old World Tropics): 160 spp. Sister to rest of family.
Quillajaceae - uncertain position in Fabales. Quillaja (temperate South America); ca 3 spp.
Rhabdodendraceae: spine below core Caryophyllales. Rhabdodendron (tropical South America): 3 spp.
Rhizophoraceae: Malpighiales. Paradrypetes (tropical South America); 2 spp., very odd genus.
Rousseaceae: Asterales - sister to Campanulaceae, basal relationships of which are poorly known. One clade includes Roussea (Mauritius): 1 sp. The other clade includes Abrophyllum (E. Australia), Carpodetus (New Guinea to New Zealand), Cuttsia (E. Australia); 1, 2, and 1 spp. respectively.
Sabiaceae - probably sister to (and to be included in Proteales. Meliosma ((sub)tropics, not Africa), Ophiocaryon (South America), Sabia (Indo-Malesia): 28, 7, and 19 spp. respectively.
Sapindaceae: Sapindales. Xanthoceras (China): 1 sp. Possibly sister to rest of family
Sarcobataceae - in core Caryophyllales. Sarcobatus (S.W. North America): 2 spp.
Setchellanthaceae, along spine of Brassicales. Setchellanthus (S.W. U.S.A., Mexico): 1 sp.
Simmondsiaceae, spine below core Caryophyllales. Simmondsia (S.W. U.S.A., Mexico): 1 sp.
Sladeniaceae: Ericales - sister to Pentaphylacaceae. Ficalhoa (East Africa), Sladenia (S. E. Asia): 1 and ?2 spp. respectively.
Stegnospermataceae: along spine of core Caryophyllales. Stegnospermum (Central America, Antilles): 3 spp.
Stixaceae - unplaced in core Brassicales, ?monophyly. Forchhammeria (S.W. North America), Stixis (E. Himalayas to W. Malesia), Neothorelia (Laos), Tirania (Vietnam): 10, 7, 1 and 1 spp. respectively.
Surianaceae: unresolved in Fabales. Cadelia (N.E. Australia), Guilfoylia (E. Australia), Recchia (Mexico), Stylobasium (W. and N. Australia), Suriana (pantropical, a little known): 1, 1, 3, 2 and 1 spp. respectively.
Tapisciaceae - in poorly known Huerteales. Huertea (Central and South America), Tapiscia (E. Asia): 4 and 1 spp. respectively.
Tetracarpaeaceae: Saxifragales. Tetracarpaea (Tasmania): 1 sp.
Tetrachondraceae - near base of spine of Lamiales. Polypremum (New World), Tetrachondra (New Zealand, Chile): 1 and 2 spp. respectively.
Ticodendraceae: Fagales. Ticodendron (Central America): 1 sp.
Torricelliaceae: sister to all Apiales minus Pennantiaceae. Aralidium (W. Malesia), Melanophylla (Madagascar), Torricellia (Southeast Asia): 1, 7, and 2 spp. respectively.
Vahliaceae: unplaced asterid I. Vahlia (Africa, Madagascar, Indian subcontinent): 8 spp.
Violaceae: Malpighiales. Fusispermum (Costa Rica, Colombia, Peru): 3 spp. Sister to rest of family.
Wellstediaceae: see Boraginaceae.
Xeronemataceae: spine of Asparagales. Xeronema (New Zealand, New Caledonia): 1 sp.
ON THE ORGANIZATION AND DESIGN OF THE SITE
This website is best viewed using the most recent version of your preferred internet browser. You can tell when each page was last updated if you look at the top of each page, or, for the individual order pages, immediately below mention of the order or other major clade first mentioned on that page - thus on the Arecales page the update indication is below the characterization of the commelinid group.
The left pane is designed as a quick reference listing. The default pane includes a reference list of accepted orders and unplaced families as well as a listing of abbreviations, etc., used in the body of the text. There are also direct links to the developing essays on seed plant evolution and also angiosperm evolution and diversification. This left pane can be replaced by a list of the main characters that are described in detail elsewhere - see the "Characters" option in the top pane of the website.
The top pane is designed as a menu:
- "Home" will always return the user to this page.
- "Tree" gets you to the Main Tree that displays a phylogeny of the orders. Clicking once on the name of a terminal taxon will take you to a characterization of that taxon. Clicking on a node will take you to that particular node. Clicking on one of the tree icons next to an ordinal name will usually take you a tree showing relationships within that order. Not all orders have such icons; some are too small. Clicking on "Unplaced Taxa" will send the user to those few families and genera that lack any convincing evidence as to their likely immediate relationships.
- "Orders" provides an alphabetical listing of all accepted ordinal names and also all synonyms. Clicking on a letter at the top of the page will take you to the beginning of names that start with that particular letter. Clicking on a link to an order will take you to its characterization. Note that ordinal and some higher-rank names were for a while proliferating notably more rapidly than those at lower ranks (e.g. see Doweld 2001c).
- "Families" is an alphabetical listing of all accepted family names and commonly-used synonyms. Clicking on a letter at the top of the page will take you to the beginning of names that start with that particular letter. Clicking on a link to a family will take you to its characterization.
- "Characters" provides a textual description of all the characters used to support the recognition and/or monophyly of a particular taxon. General references that are important sources of data for this project are also included. At the beginning of this page is a notice "click here"; this will display a list of the major characters included in the left pane. One can return to the Orders list by choosing the option "Back to Orders" at the beginning of the character list.
- "References" is an alphabetical listing of the references cited here; it has been broken down into six interlinked pages for ease of loading. Clicking on a letter at the top or the bottom of the page will take you to the part of the reference list where surnames with that letter begin. Articles with two authors are listed alphabetically by name of second author and then by date, articles with three or more authors are cited last (e.g. as "Chase [et al. 1993]") and are listed by date. Much of the older literature in which there can be invaluable character surveys is now coming on line, for example, see the Botanicus Digital Library which will soon be approaching 1,700,000 pages scanned while the Biodiversity Heritage Library has almost 30,500,000 pages scanned (as of 17.vi.2010). For a useful device that will provide recent literature, etc., for individual species, see Rod Page's iSpecies, Wikipedia, the Encyclopedia of Life, etc.
- "Search" takes you to a page where you may enter keywords or terms that you are interested in finding within the Angiosperm Phylogeny Website. The search engine is unfortunately not designed to search for wildcards, so if your search is not successful, please try variations of your search terms. We are using PicoSearch.
- "Links" lists some other websites or web utilities that are relevant to general classification, floras (a few), image resources, and phylogeny. These listings are very incomplete. Links to other websites will also be found in the bibliography and in individual ordinal pages.
- The "Glossary" is made up of three separate pages. Clicking on a letter at the top or the bottom of the page will take you to the first definition starting with that particular letter. Within the Glossary, we have built in cross references to characters at the same level. Thus when reading the definition of paracytic stomata, you will find direct links to other types of stomata such as anomocytic, cyclocytic, etc. There are links to definitions at other levels, e.g. to stomata in general, where the basic features of stomata are described, and also to variants of individual stomatal types such as brachyparacytic stomata. We have also built in some synonymy, e.g., Rubiaceous stomata are a synonym of paracytic stomata.
Note that the names on the images of plants may not have been brought up to date - do not worry! Furthermore, we did not chose the most spectacular photographs we could find, rather, I tried to select those that showed at least some features on the plant that help characterize the group to which it belongs. All photographs are copyrighted as is evident from the characterizations or the images or the external websites themselves. For photographs of individual species, or simply for more images of families, use Google or iSpecies.
ON THE INTERPRETATION OF THE TREES, TEXT, ABBREVIATIONS, ETC.
In the trees in this site I have emphasized mostly nodes with substantial support (e.g. ³80% bootstrap support) that appear after analysis of data from more than one gene; by and large there is little conflict between different studies when they overlap. In a few cases I have been somewhat less cautious, but I have always tried to make it clear where I am treading on thin ice; references are always given. In such cases, future studies may lead to slight changes in the topologies of the trees, or they may confirm them, as may be seen when reading the discussions of relationships of Saxifragales and Gunnerales. There are references (not exhaustive) to papers giving support for the relationships suggested here, and these papers often have more resolved trees than those shown, albeit that details of these topologies may on occasion have little support. Chase et al (1993, 2000a), Olmstead et al. (1992, 1993, 2000), Olmstead and Graham (2000a, b), Savolainen et al. (2000a, b), D. Soltis et al. (1997, 1998, 2000, 2003, 2005b), P. Soltis et al. (2000), B. Bremer et al. (2002), Hilu et al. (2003), Jansen et al. (2007), Saarela et al. (2007), Moore et al. (2007, 2010), etc., are invaluable sources for the developing big picture of angiosperm relationships.
If one printed out all the trees in this site and stuck them all together, it might seem as if one had some kind of super tree, however, it is clear from the description of my modus operandi that these trees are hardly a formal super tree. Readers who are interested in the topology of the most parsimonious tree, or relationships suggested by poorly supported nodes, etc., should consult the original literature. PhyloMatic is a another resource to be used. In studies that use Bayesian analysis it must be remembered that posterior probabilities for a particular node are usually substantially higher than its bootstrap or jacknife values.
For an introduction to the interpretation of phylogenetic trees, see Baum and Smith (2012). Krell and Cranston (2004) and Crisp and Cook (2005) and many others have emphasized how careful one must be when interpreting and talking about ladderised trees (see above) in particular and phylogenetic trees in general. The use of the adjective "basal" is especially dangerous (see also D. Soltis et al. 2005b). When I use the term, and the context is not otherwise clear, I am referring to the pectinations at the base of a ladderised tree; note that when talking about sister taxa, one cannot be basal to the other! The word "primitive" should practically never be used, especially when talking about taxa. Amborellaceae and Pinaceae are sister to all other flowering plants and Pinales, respectively, but that does not necessarily mean they are "primitive"; Pinaceae in particular have numerous apomorphies. The words "ancestral" or "plesiomorphic" are far less loaded than primitive, and can be used to talk about individual characters; derived and apomorphic (but not advanced) are their opposites.
In connection with this ladderisation of the trees, comments on particular nodes - whether subtending dichotomies or polytomies - are to be found under the first branch (reading from left to right) on the tree, although there are direct cross-links between pages to other branches in important cases. Thus comments on the relationships of the magnoliid group as a whole, which include relationships between Chloranthales, monocots, Ceratophyllaceae and eudicots, are to be found on the Magnoliales page alone, however, this discussion is cross-linked between the relevant pages. However, comments on relationships within the magnoliid group itself are to be found only on the Magnoliales page, and not on the Laurales, Piperales or Canellales pages.
The information on each page is to be read as if you were following along from the base of the seed plant tree to the point on one of the branches to which you have gone. Thus each page starts off with a characterisation of the common ancestor of all seed plants, then of angiosperms, and then characterisations of all nodes on the branches leading up to the order in question. As you read up the tree, you may find apparent contradictions. These mean that the feature mentioned more basally in the tree (earlier on that page) has changed, perhaps even reversed. Thus at the node [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]] you will find "ethereal oils +" - this part of the tree seems to be where that feature evolved. However, the apomorphies of [CERATOPHYLLALES + EUDICOTS] and of all monocots minus Acorales show "ethereal oils 0". Ethereal oils have also subsequently been reacquired several times, as in Zingiberaceae, within Lamiaceae, etc.
I very largely follow the families and orders recognized by the Angiosperm Phylogeny Group (A.P.G. III 2009), with modifications suggested by more recent work (see individual pages). Families are grouped within orders as far as possible according to their phylogenetic relationships.
Trees showing relationships within many orders - and a few of the larger families - are included. Note that they may have been cobbled together from more than one study. Remember that these trees, too, are conservative; to help the user I usually give some indication of support for the nodes on the trees. Further details of relationships can be found in the papers cited, which should always be consulted.
For the authorities of the names of subfamilies, families, orders, etc., I have relied largely on Reveal's listings (Reveal 2001 onwards) and especially Hoogland and Reveal (2005) and Thorne (with Reveal) 2007. The first should be consulted in case of doubt, since the authors of some names as given here may be incorrect and bibliographic work that affects authority names proceeds apace. Synonymy is as complete as I can get it at the familial level and above; a few family-level synonyms remain unassigned to subfamilies when the latter are mentioned. A few family or generic names may also be used as headers for groups within families; these inconsistencies will be cleared up as phylogenetic patterns become clearer and appropriate nomenclatural proposals are made. Paraphyletic groups are clearly indicated as being such.
Features are mentioned in the characterisations roughly following the order in the discussion of the characters on the "Characters" page. Possible apomorphies are indicated, but it will be abundantly clear that fixing characters to nodes is no easy task. For some characters (an example is leaf ptyxis) there is little easily-accessible basic information and the terms used to describe it in the literature are not used consistently. It is not always recorded in the characterisations below, although its coverage is slowly improving; the same is true for the pattern of petiole vasculature, presence of pericyclic fibers in the stem, etc.; I had initially not considered such characters to be particularly useful (and this indeed may be true of petiole anatomy). Gaps in data are often indicated, but for many features confidently included in a characterisation, e.g. micropyle type, it should not be forgotten that this may be known for very few taxa. The contraction P stands for perianth, T for tepals, K for calyx, C for corolla, A for androecium, and G for gynoecium. "#<" means equal to or more than, "<#" means equal to or fewer than. "Many" means that there are more than fifteen or so parts. Parentheses in characterisations of clades above the level of family denote characters that are scattered throughout that clade, being found in several, but not all, terminal taxa but in no obvious pattern. Examples are septal nectaries and cuticle waxes in monocots, N-fixing in part of the eurosid I clade, and iridoids in asterids. Parentheses in characterizations of terminal taxa refer (as in conventional descriptions) to uncommon features. Square brackets enclose explanations or glosses of the feature described. When a generic name is placed in square brackets after mention of a feature, this emphasized that the feature is known from/I know of it from only that one genus. However, square brackets surrounding carpel number means that the carpels are connate, at least as to their ovule-bearing parts. A line under the number of carpels means that the ovary is superior. A fuller list of abbreviations, etc., used may be found under "Abbreviations" on the top of the left pane.
Following familial and subfamilial characterisations are two figures, the approximate number of accepted genera and species in the group. I mention most genera with 50 or more species and estimate total numbers of species and genera in families; much of this information is taken from Mabberley's excellent The Plant Book (Mabberley 2008) as well as from accounts in Kubitzki (1993 onwards). A list of included genera and their synonyms can often be found by clicking on "list". This will often take the user to a database of Vascular Plant Genera and Families that is maintained by the Royal Botanic Gardens, Kew. However, the genera accepted there may not always be the same as those now accepted, and the family limits there may be different than those adopted here. In other cases the user is taken to lists of accepted genera developed for families recognised by Angiosperm Phylogeny Group by Mark Chase, Dick Olmstead, and many others, however, these do not include synonyms; in yet other cases, the lists are original. Between them the patient user will be able to answer most questions bearing on the authorities of generic names and on commonly-used synonymy. There are also links to images.
General distribution is indicated, and some hundreds of distribution maps have been added; these are amended as more information becomes available, and there are yet others in process. These give only overall indications of natural - i.e. unaffected by recent human activities - distributions, and I have usually made little attempt to plot the distributions of plants on oceanic islands. The best resources for distributions are dot maps, and in many cases the original outline maps on which many maps here are based have had to been amended, for instance, as substantial holes in the distributions of many apparently widely-ranging families have become apparent - indeed, it has proved surprisingly difficult to find/make accurate maps. Major resources include Hultén and Fries (1986: see also Hultén's earlier work), van Steenis (1963), van Steenis and van Balgooy (1966), van Balgooy (1975, 1984, 1993), Meusel and his collaborators (Meusel et al. 1965, 1978, 1992), and Quian and Ricklefs (2004: see electronic appendix, corrections of the often rather vague maps in Heywood ); invaluable maps for tropical Africa are appearing, see Lebrun and Stork (2003 onwards). Some maps in Heywood et al. (2007) have been used as a last resort. There are various online resouces appearing, including the excellent FloraBase, for the flora of West Australia, and Australia's Virtual Herbarium, for the flora of Australia as a whole; BONAP's Taxonomic Data Center for the north American flora, also provides a useful check on the distributions of plants given in general maps. Maps generated by searches on GBIF and Tropicos can be helpful, but there in particular beware of records from cultivated plants, aliens, etc. I have included the distributions of fossils in cases when they clarify the distributions of extant taxa. Sources for the maps are indicated.
Infrafamilial classifications for some of the larger families - and additional trees and maps, where appropriate - are being added as well supported classifications appear.
Following most families and a very few orders are brief paragraphs giving characters that I find to be helpful in recognizing the taxa; the terms used here may not be perfectly "correct" botanically. Some of these features are taken from LaFrankie (2011), while Utteridge and Bramley (2014) suggest how the commoner tropical families can best be recognized.
There are a number of sections with subheadings following the family accounts (and also at higher nodes in the tree when relevant). Most of these sections were introduced starting late 2008. Age refers to crown-group ages, and these are placed at the eppropriate node. However, ages at this stage of our knowledge are unreliable, and in several cases there are substantially different estimates for the same event, so treat these dates with particular caution. Evolution includes discussion on diversification and biogeography (Diversification & Distribution), comments on mycorrhizae and photosynthetic variants, etc. (Ecology & Physiology), on fungal and bacterial associations in general (Bacterial/Fungal Associations), herbivory and galling (Plant/Animal Interactions, information on pollination and disseminule distribution (Pollination Biology & Seed Dispersal), and Genes & Genomes.
In the paragraph Economic Importance is included only a few of the economically globally important taxa, and this part is currently notably incomplete. The section Chemistry, Morphology, etc. summarizes interesting variation within the family and includes referencess to major sources of information that are not mentioned elsewhere. In the Phylogeny section there are summaries of major phylogenetic works bearing on our current ideas of phylogentic relationships in the family. In the section Classification can be found references to the infrafamilial classification followed here, and there is some discussion about generic limits in the family and sometimes mention of important recent monographs of groups in the family. Insofar as there is discussion about earlier ideas of relationships (Previous Relationships), I mention largely some suggestions of Cronquist (1981) and Takhtajan (1997), but only because their work is still used. Finding out who was "first" in suggesting a particular relationship is no goal of these pages, the more so since what is often more interesting is not that a particular suggestion was made, but exactly why it was made. Trivia needs no explanation. There is a complete family-level and above synonymy at the appropriate place on each page.
General referencing has holes in part because of the origin of these notes as a teaching aid and in part because I include very largely references from which I have actually taken information. There are additional references on the "Characters" page to general surveys or other sources of information for particular characters; these may not be mentioned elsewhere. Other references to variation of particular characters within and between families may be found in the discussion after the characterisation of the orders or families. Note that many of the older "family" and "order" references include information about other groups, some of which would not now be considered at all close.
In the "Glossary" pages we attempt to provide accurate definitions of the terms commonly used in the site and some other terms that may be encountered, representative chemical formulae, etc. Definitions as far as possible follow current usage, rather than etymology or original definitions (see, e.g. Rickett 1954-56). Building this glossary has forced me to confront head-on such problems as the plethora of terms used to describe inflorescences (in part resolvable, I think, providing one does not attempt too much detail) and fruits (more difficult). Botany needs a simplified common language, but this can be developed only if the botanical community as a whole agrees on definitions and synonyms. A goal of botanical terminology must be to simplify the terms we use and to try and reduce the number of synonyms in common use.
!!IMPORTANT - WARNING TO ALL USERS!!
All clades are hypotheses of relationships, and as hypotheses they may be overturned. Even though I have for the most part been conservative, changes in our ideas of relationships, and hence in the clades we talk about, are still likely in places like parts of Caryophyllales, etc.. Taxa whose relationships are still largely unknown or only partly known - apparently not many, although we must expect to find a few more seriously misplaced genera - should also not be forgotten. Thus some changes are to be expected, but change is neither a defect of cladistics nor a necessary consequence of the use of molecular data.
A very important issue for all morphological studies, particularly at this level, is the documentation of variation within a character and the justification of the states that are used to describe this variation. As I often mention, the states used have frequently been inadequately justified, explicit criteria for their delimitation not having been presented. Character states that lack justification may or may not compromise a phylogenetic analysis, but there is certainly little reason to talk about their evolution (Stevens 2000 for literature). To quote Heywood (1973: p. 311) slightly out of context, "Systematics can be likened to a mincing machine into which data of all sorts is fed and processed to form a series of sausages ... The basic recipe for the construction of these "sausages" is usually secret, yet it is such encapsulated pieces of information that we have to work with and communicate with." Observations and literature should be directly linked at the level of individual species and specimens, and this would allow the problem of wrongly assigned taxa to be dealt with - remove a taxon from a family, and all information in a database that is linked to that taxon would be removed at the same time. Furthermore, this linkage would most readily allow variation to be understood within the context of developing family phylogenies (see also below) Finally, character states for conventional morphological phylogenetic analyses at the angiosperm-wide level can be delimited only after the inspection of all relevant variation shown by a character. Thus variation in the thickness of the nucellus or the thickness of the integuments should be divided into states only after assembling the data on the number of cell layers in these structures in all angiosperm genera where known. Or not. If variation is fitted to a tree, a preferable course if one is studying morphological change over time, character states in the sense just discussed will not be needed. One of our goals is to understand the evolution of form, and character states as conventionally delimited may not be as helpful to us in this endeavour as we might like or think.
Remember that for many character states included in the characterizations our basic knowledge is often incomplete at the family level, and certainly sampling within the families is inadequate. Also, I have included less information about chemical, wood anatomical, palynological, and embryological characters than I might. This is because for chemical characters (for example), my basic knowledge needs improving, while for some of the other more cryptic characters the sampling may be poor and state delimitation suspect. But equally importantly, these notes began as teaching notes, and I judged that there was more than enough for the student or even the teacher to be going on with. However, an ideal system would include everything(!) of value, and the user could then remove detail that was judged unimportant for the purpose at hand - indeed, I am slowly adding more detail where I feel confident.
Subfamilies or tribes are numbered sequentially within each family. Although many of their characterisations are only imperfectly worked out, they help clarify which family characters really are potential synapomorphies and which simply characterise only parts of the family, speciose though those parts may be, and whether the age for a family is the crown-group age of the family as a whole, or just of part of it. The importance of having infra-familial variation pegged to its correct level is evident in, for example, Annonaceae, Convolvulaceae, and Fabaceae. "Family" apomorphies may turn out to be apomorphies for only part of the family.
That I mention some features as not being known is in many cases simply an expression of my ignorance.
There are still one or two generic groupings in the text that are unassigned to families (see e.g. the Garryales page) and a few families are not placed in orders.
This site is updated on a more or less continuous basis. I teach plant families every other year and this is a particularly good time for finding areas that need attention.
I will be more than grateful if any references in the text that lack citations and any errors of omission or commission are brought to my attention - firstname.lastname@example.org should find me.
Spelling is erratic and somewhat mid-Atlantic; grammar is little better. All errors are mine.
HISTORY OF THE SITE
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These notes began as I taught Biology 103, the basic plant families course, at Harvard, taking over from Carroll E. Wood, Jr. (an impossible task). They became more wide-ranging when I twice taught OTS "Tropical Plant Systematics", and when I attempted to deal with all families in a one-semester, graduate-level course at Harvard. This last was a failure; we did not get to the monocots. However, the time and energy spent in assembling material for each class from all corners of the herbarium convinced me like nothing else could have that the modified Englerian system the herbarium then followed was didactically a disaster. Finally, I have long been interested in sight identification of herbarium material; unidentified specimens have to be brought into the system somehow. I have done this intermittently, but as frequently as I could, over the years, often with students and others, and this has been invaluable both in reviewing characters and also in learning more.
The first version of the website (version 2) that was made generally known included literature that appeared as late as early August, 2001; the Introduction to this version is dated the 13th of July 2001. Version 2 benefited from teaching again in Costa Rica. This time I was with InBio personnel, and I learned perhaps more than I taught; a course given at the University of Campinas, in Brasil, was similarly stimulating.
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What happens with these pages depends on how useful they are found to be, or can be made to be. Their goal is to help in teaching, although I find them also a useful research tool in that they help direct one's attention to interesting characters and to taxa that are poorly understood. They are not intended to compete with other web sites that depict the tree of life, etc.
Filling in gaps in the literature continues to improve family characterisations; three character systems in particular, chemistry, wood anatomy and palynology, clearly need more attention. We will continue to build in more links to photographs and to other web sites, particularly those that focus on families. Adding good diagrams showing the basic floral morphology of each family would be very helpful (see Ronse DeCraene 2010 for recent work on floral diagrams; Eichler 1875-1878 remains invaluable), and simple floral formulae are also to be desired (see Prenner et al. 2010; such diagrams can seem like a new language...; Simpson 2010 suggests other symbols that might be useful). However, as with the three delinquent character systems just mentioned, a substantial effort is involved. The main goal for this next year or so (2010-2012) is to tap in to or develop a system that assigns all generic names to their correct A.P.G. family.
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Last, but certainly not least, I thank Kobinah Abdul-Salim, Stuart Davies, Diane Ferguson, Rick Ree, George Weiblen and Barbara Whitlock for providing the impetus to start this. Students at courses at Harvard University, Massachusetts, InBio, Costa Rica, the University of Campinas, Brasil, and the University of Missouri, St Louis and Missouri Botanical Garden have worked with successive versions of the hierarchy, uncovering flaws as they did do; to them my thanks for their enthusiasm and tolerance. Librarians at Harvard University and the Missouri Botanical Garden have been unfailingly helpful in finding sometimes obscure references. A few sections have been read by colleagues who are thanked individually in the text. Many people have sent in comments and/or noticed mistakes; my thanks to you all, although I have not mentioned you individually unless you have caught particularly egregious errors! Mark Olson, Beth Owen and Bob Magill helped to set up the site. Finally, to say that I am extremely grateful to Hilary Davis for building the site, adding the links to the Gentry photographs of the Missouri Botanical Garden, and generally helping things along, is an understatement.
P. F. Stevens, 13 (Friday) July 2001 - University of Missouri, St Louis, and Missouri Botanical Garden.
I inexcusably forgot to thank Dr Barry Hammel (Costa Rica) and Drs Maria Amaral and Volker Bittrich (Campinas, Brasil) for their invitations to teach/learn from InBio personnel and University of Campinas staff and students respectively. For version 3, many have been kind in either giving us their photographs or allowing us to make direct links to their photographs: Atlas of Florida Vascular Plants, Arizona State University Herbarium, Australian National Botanic Gardens, David Boufford - Biodiversity of the Hengduan Mountains China, Mark Brand - UConn Plant Database, CalPhotos, Connecticut Botanical Society, Michael Dillon - Andean Botanical Information System, Michael A. Dirr, Murray Fagg - Australian National Botanic Gardens, Gardenweek.org, Christine Howells - Australian Plants Society Tasmania, Kelly Irvin - International Bulb Society, Don Les, John Maunder - Provincial Museum of Newfoundland and Labrador, Kate McCombs - Christchurch City Council New Zealand, Andrew Morgan - University of Tasmania, Clinton Morse - University of Connecticut Greenhouse, Mount Tomah Botanic Garden Australia, Lytton J. Musselman, Dan Nickrent - Parasitic Plant Connection, Plant of the Week - Smithsonian Institution, James Reveal, George Schatz - Madagascar Conspectus Website, Thomas Schöpke, Tim Stephens - University of California Santa Cruz, Kurt Stüber, Jim Mann Taylor, Texas A&M Bioinformatics Working Group Vascular Plant Gallery, Brian Walters - Australian Society for Growing Native Australian Plants, Len Webb Ecological Images Collection, Western Australia Seagrass Website, Steven J. Wolf, University of Wisconsin Plant Systematics Collection. Gerald Carr and Heinz Schneider have been particularly generous in making available many magnificent photographs; these are but some that can be found at the sites that the two maintain (Vascular Plant Families Image Gallery and Botanical Image Database, respectively). Dave Boufford has caught many errors throughout the site, as has Paul von Rijckevorsel. I am again grateful to students at the University of Missouri at St Louis, Washington University, and St Louis University, and to staff and visitors at the Missouri Botanical Garden. And once again, my sincere thanks to Hilary Davis, to whom the improvements of the site are due.
P. F. Stevens, 15 May 2002 - University of Missouri, St Louis, and Missouri Botanical Garden.
Once again, the normal list of suspects is to be thanked. Many people have written in with comments that, whether apparently trivial or cosmic, I have tried to take into account. I remain grateful to students at the University of Missouri at St Louis, Washington University, and St Louis University, and to staff and visitors at the Missouri Botanical Garden. Hilary Davis continues to improve the site.
P. F. Stevens, 2 May 2003 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 4 was archived on May 1. I again thank students at the University of Missouri at St Louis, Washington University, and St Louis University, and all who have caught mistakes, suggested additions, etc. Hilary Davis has worked hard on the site, especially the glossary, and she plans further improvements.
P. F. Stevens, 5 May 2004 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 5 is being archived today, Sunday May 22. All those who have caught mistakes and made suggestions are gratefully thanked, and Hilary Davis is particularly thanked for developing the protocol for making the maps. She has also developed a protocol for integrating illustrations of critical characters with the text that we will try and implement this next year.
P. F. Stevens, 22 May 2005 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 6 was archived on Sunday May 21. All those who have caught mistakes and made suggestions are gratefully thanked, and Andrew Ford has been particularly helpful. The library staff at the Missouri Botanical Garden have patiently dealt with a positive barrage of queries this last year, and I thank Victoria McMichael and Mary Stiffler in particular for their tolerance. Hilary Davies continues to help developing the site.
P. F. Stevens, 22 May 2006 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 7 was archived on Sunday, June 3. I am particularly grateful to students in my plant families course for making this last term so stimulating, and spurring the development of a new section of the site, the "Student" section, which Hilary Davis put up just prior to archiving. Again, the library staff have been swamped with requests, and again corrections and additions have been suggested; I thank all who have been involved in this project, no matter how apparently peripherally.
P. F. Stevens, 8 June 2007 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 8 was archived on Friday, May 30th. The "Student" section has occupied my energies for much of this year. I thank Felipe Zapata for bringing literature to my attention, making suggestions, etc., Hilary Davis for continuing to persevere with this project, and all who have suggested additions and corrections.
P. F. Stevens, Monday, May 26th, 2008 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 9 was archived on Friday, June 19th. In connection with suggestions made by Amy Zanne and Cam Webb, I have been working at making the discussion more rational, introducing a number of subheadings which I hope will make it easier to navigate. Felipe Zapata and Hilary Davis have continued to help with this project, and I thank all of you who have sent me additions and corrections.
P. F. Stevens, Sunday, June 21st, 2009 - University of Missouri, St Louis, and Missouri Botanical Garden.
I have just realised that I omitted to say that version 10 was archived on on July 7th; the year has been very hectic. I am not as far along with the reorganization of the site as I wanted to be, but hope springs eternal. Cam Webb, Amy Zanne, Felipe Zapata and Hilary Davis continue with the project, and again I thank all of you who have sent me additions and corrections; the "small" errors often point out larger problems.
P. F. Stevens, Saturday, November 20th(!), 2010 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 11 was archived on May 21st. Unfortunately, this year was no better than the last... Thanks Cam, Amy, Felipe and Hilary for continuing to directly or indirectly prod, and to all for corrections; trees will have to be updated in the very near future!
P. F. Stevens, Saturday, May 28, 2011 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 12 was archived on July 25th. The whole site is in the process of being reworked, and this has exposed the consequences of adding bits of information sporadically over a long period of time... In addition, with the help of Cam the apomorphies - many of which have been added this past year - are being given xml tags, and these will shortly be extended to the discussion, the nodes, etc. Thanks to Amy, Felipe and Hilary for continuing help, the staff of the library at the Garden who have deat with even more of a barrage of requests than usual, and to Volker Bittrich and to all the rest of you for comments and corrections.
P. F. Stevens, Tuesday, August 1, 2012 - University of Missouri, St Louis, and Missouri Botanical Garden.
Version 12 was archived on September 26th. The reworking of the site has continued - apomorphies have now been flagged throughout the site, and dates for clades, which were in a considerable mess, are being cleaned up. Given the reorganisation of the site over the last couple of years, the "Student" section has been removed, as has the "Apmorphies" section (it is now redundant) and the "Statistics" section (that was simply one more area to keep up to date, and anyhow, I had largely ignored it).
P. F. Stevens, Tuesday, September 28, 2013 - University of Missouri, St Louis, and Missouri Botanical Garden.
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