On classifications in general, and this classification in particular.
On forming clade characterizations (and thinking about apomorphies).
On the organization and design of the site.
On the interpretation of the text, abbreviations, etc.
Important - Warning to All Users!
Website developed and maintained by Hilary Davis: hilary.davis@mobot.org
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 is clear (see the Angiosperm Phylogeny Group II 2003). Furthermore, as details of phylogeny are clarified and new findings made in anatomy, morphology, etc., they can be rapidly integrated 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 Books are out-of-date before they appear, furthermore, there is no comprehensive phylogeny-based treatment of angiosperms, out-of-date or not; D. Soltis et al.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) is 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) and Simpson (2005).
The focus of this site is on angiosperms, 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 for the most part monophyletic - around which many of us organize our understanding of plant diversity. I also pay attention to groupings of families because much progress has been made in the last decade in particular in sorting them out. Infrafamilial groups in groups like Poaceae, Malvaceae and Ericaceae are also included in these pages, and these are being added to as studies become available. In larger families I tend to focus on literature that deals with fifty or more taxa, in smaller families the coverage is more detailed.
We don't want to know merely about clades, we want to know what makes clades unique, the synapomorphies or shared derived characters of those clades that first appeared in the immediate ancestors of those clades. However, for the most part our knowledge of synapomorphies associated with the taxa characterised here remains poor. As we will see, finding out the composition of clades can be easier than finding the synapomorphies for the same clades (see the Apomorphies page and discussion below). And of course knowing about synapomorphies is just one aspect of understanding the whys and wherefores of the evolution and diversification of seed plants, our ultimate goal.
ON CLASSIFICATIONS IN GENERAL, AND THIS CLASSIFICATION IN PARTICULAR
On classifications in general
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. For any biological 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 (Stevens 2006a for references). Phylogenetic classifications convey aspects of our knowledge about the phylogenetic relationships. Thus a family is clearly flagged as such and is a monophyletic group that can contain several genera, also flagged as such and also monophyletic, but a genus can never include families. Generic, family, etc., names are simply words we use to denote appropriate parts of phylogenies and minimal aspects of their relationships.
Thus I use a flagged hierarchy here for naming taxa. The rank terminations used (-ales, -aceae, etc.) suggest relative positions of groups in the local hierarchy. If Ericaceae and Vaccinioideae are part of the same monophyletic group, the latter must refer to a clade contained within the former, even if neither can necessarily be directly compared with Polemoniaceae and Cobaeoideae (other than all being monophyletic groups). Taxa at the same rank are equivalent only by designation and have nothing necessarily in common (unless they are sister taxa) 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. Such a flagged hierarchy is useful as a mnemonic and communication device (e.g. Stevens 2006a; see also Valentine & May 1996 for hierarchies). It improves memorization, and emphasis on families and orders, as here, is a didactic device - families are monophyletic units useful in communication, major units learned by biologists and others world-wide.
The distinction between grouping and ranking is extremely important, as is how we interpret the latter. 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 have often been treated incorrectly as if they were equivalent by biologists attempting to understand evolutionary or biogeographic problems (see Bertrand et al. 2006 for detailed discussion), even if those constructing the classifications were explicit about the non-equivalence of taxa at the one rank (see Darwin 1859; Stevens 1997; Bertrand et al. 2006). In fact, rank terminations have relatively infrequently been used to reflect 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 somehow being comparable entities, are class hierarchies in the strict sense - Stevens 2002, 2006a). However, 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 potential problems caused by this eurocentric bias).
It has been suggested that taxon rank be adjusted so that rank somehow reflects the degree of morphological differences between taxa, or that taxa at the same rank be based on similar characters, or show a similar amount of distinctness. This might be possible using phenetic methods of analysis, but is very difficult if one's classification is phylogeny-based, as here. It has also been suggested that group rank could be made to depend on the age of the clade (e.g. Hennig 1966). Apart from the fact that aging times of divergence of clades is still a rather difficult enterprise, huge disruptions to our nomenclature would result, so much so that recent suggestions which invoke the use of age in classifications focus on providing a standardized timeclip, i.e. set of letters referring to a particular geological period, to be added to the conventional taxon name (Avise & Mitchell 2007).
Turning more specifically to phylogenetic classifications in general, and to the particular classification used here, Backlund and Bremer (1998) provide a useful discussion on the principles of phylogenetic classification that is applicable at all levels apart from species (see also Stevens 1998; also Albach et al. 2004; Entwisle & Weston 2005; Pfeil & Crisp 2005, etc., for examples). 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 cf. the PhyloCode - Cantino & de Queiroz 2006). Additional criteria can be invoked. Other things being equal, it is helpful if 1, taxa formally recognised are easily recognizable, 2, groups that are well-established in the literature can be 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 change be minimized. Somewhat similarly, Godfray and Knapp (2004: p. 562) note that "users want stable, informative and accessible classifications that enable easy identification" - although invoking "users" without specifying those who make up this group is not very helpful. This classification 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.
The accessory principles of Backlund and Bremer should be used in combination. Thus keeping the monogeneric Platanaceae separate from its 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, 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. The continued recognition of Valerianaceae and Dipsacaceae also runs into this problem (see also Pfeil & Crisp 2005; Orthia et al. 2005; Albach 2008, etc., for useful practical discussions of such matters). But there are no absolute guidelines. If Podostemaceae turn out to be sister to Clusiaceae - Hypericoideae (for references here and elsewhere in the Introduction, see the relevant order pages), one can imagine a phylogenetic situation in which some dismemberment of Clusiaceae s.l. would not be too high a price to pay for the continued recognition of Podostemaceae. Hence the somewhat provisional recognition of Hypericaceae as well as Clusiaceae below; the families can all be recognized, and the name Podostemaceae in particular is very well established. In 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, might have to be recognised as a family, too, but Araceae in a somewhat restricted sense would be somewhat more morphologically coherent, although not greatly so...
Note that problems with this emphasis on monophyly may be caused by reticulation events such as hybridization, endosymbiosis, and lateral gene transfer, but they are unlikely to be confusing factors here; of course, there are further problems with species, and strict monophyly is a less important criterion there (see much of the discussion in Hörandl 2006). Genera can often be pegged to above the level at which hybridization is at all common, although in Poaceae-Pooideae there are some intractable problems where extremely well established common usage and the principle of monophyly are likely to remain at odds, as around Triticum (Petersen et al. 2006). The endosymbiotic events that characterize the clade of which flowering plants are a part are very ancient and cause no problems for the student of multicellular organisms. Lateral gene transfer has been detected in a number of situations between quite unrelated organisms (e.g. Bergthorsson et al. 2003: Amborella and liverworts; see also below), but it, too, does not seem to present major problems for a systematist, although it raises all sorts of biological questions. Although there is increasing evidence for the importance of genome duplications in the evolution of seed plants and of palaeopolyploidy events within e.g. the Lauraceae and Magnoliaceae clades (see the Characters page for further discussion), this, too, does not currently seem to pose problems for the adoption of monophyly as the sine qua non of groups to be recognised formally in a phylogenetic classification.
Thinking of aspects of size, 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 (Stevens 1997, 2002). 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.
Takhtajan (1997) has suggested that smaller families are more "natural". This is incorrect. Monophyletic groups that include fewer taxa - Takhtajan's smaller families - do not necessarily have more apomorphies than larger groups, even if all members of smaller groups are likely to have more features in general in common. That is, they will have their apomorphies, their unique features, as well as progressively more plesiomorphies, features found both in the small groups and in the larger clades of which they are a part; "having more features in common" is indeed one common meaning of "more natural". (Note that the implication of the word "natural" has long been "a group of the kind [usually unspecified] that I think should be recognised", and so its use is rarely helpful - it is not used here.) Furthermore, if this approach is adopted we will find a slippery slope ahead. By this kind of argument all families should be very small, since their members will have a great deal in common, and so will be most "natural". 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. However, 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. Takhtajan's suggestion that narrowly defined families are more useful for phylogenetic studies may be true. 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). However, this is largely a separate issue.
There is 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 APG (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 applicable when it comes to dividing genera; little other than another headache is gained by splitting genera such as Drosera and Gnetum (Doweld 2000) as has recently been proposed. Thus if an established group divides into two (or more) clades, this is not a signal for recognising two groups at the same level. Along the same lines, if a newly-discovered taxon is sister to an existing named taxon - say a genus - this does not necessitate the description of a separate genus for the newly described species. A principle from evolutionary classification is also relevant here: The size of the gap between two groups tends to be inversely proportional to the sizes of the groups involved (Davis & Heywood 1963), although some have suggested that the sizes of gaps between groups at the same rank should be similar (Thorne 1976).
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 change.
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, particularly other than species, can be established only by convention and consensus (e.g. Stevens 2002, 2006a; Entwisle & Weston 2005). Given the increasing support for the outlines of angiosperm phylogeny, 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; Grass Phylogeny Working Group 2001; Mabberley 2008: Hibbett et al. 2007 for a good example in fungi). Reaching such a consensus is vital, 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. Our goals as systematists are surely to produce robust hypotheses of relationships, to understand the evolution of morphology, and the like - but to argue whether something "should" be a family or a subfamily? 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 cf. Baum et al. 2004; for the PhyloCode, see Cantino & De Queiroz 2006) an unflagged hierarchy is used in which any terminations of names used are uninformative about the relative position of taxa. Here, too, some consensus over the clade names commonly learned by students and used in herbaria is needed, otherwise communication will be impeded. Note that if one adopts the principle of phylogenetic naming one does not have to worry about the nomenclatural consequences caused by lumping or splitting and any well-supported clade can be named without affecting the name of more or less inclusive clades. Unfortunately, unflagged hierarchies have very serious deficiences as communication devices because they lack one aspect essential in language, biological or otherwise - 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 - but only as it pertains to individual branches, and current proposals do not even mandate that the prefixes be employed consistently - to be conveyed.
So if hypotheses of phylogeny remain stable, we should be able to base a stable classification on that phylogeny, and then get on with our work, that is, testing the phylogenies we have, elucidating phylogenies in areas where relationships are 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 utilisation in technical literature, also floras (e.g. van der Meijden 2005), dictionaries (Mabberley 2008), more popular literature (e.g. Souza & Lorenzi 2005; Spears 2006), and as an outline for a new herbarium sequence (Haston et al. 2007) is gratifying. Returning to Godfray and Knapp's (2004) users of classifications who want a stable, informative and accessible classification that enables easy identification - they want cake with everything - these pages attempt to satisfy as many of their needs as possible.
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 years coupled with a number of morphological studies that can be evaluated in a 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. Along the same lines, almost three quarters of the orders recognised by Cronquist (1981) are not monophyletic (44/59, monofamilial orders ignored), i.e. they do not contain all and only the descendents of a common ancestor, and most of the monophyletic orders are very small (Zingiberales, with eight families, were the largest); for families, somewhat over one third are not monophyletic (81/273). Interestingly, in both cases, non-monophyletic groups were proportionately rather fewer in monocots than "dicots", and about one half the families were paraphyletic compared to very few of the orders.
Here I very largely follow the Angiosperm Phylogeny Group classification (APG 2003), although with one or two more orders and with a number of unplaced families in slightly more resolved positions in the tree. These 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 (see APG 1999 for the principles underlying the classification), but recent phylogenetic work does not contradict the major outlines of the trees used by APG II (2003) or even APG I (APG 1999). Indeed, this work does not suggest other than 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). Phylogenies in the area of main interest in this site are overwhelmingly tree-like, although there is evidence for acquisition of host plant genes by parasites (see below), even wider but inexplicable transfer of mitochochondrial genes in plants like Amborella (Bergthorsson et al. 2004), and even transfers of nuclear genes (Vallenback et al. 2008), these are the exception rather than the rule.
Most trees on this site have been more or less ladderized, which in this case means arbitrarily showing the smaller (in terms of numbers of terminals) sister taxon on the same side at every node, thus the trees tend to be pectinate. (The ladderization may be imperfect, for example, one can see that on the Main Tree asterids, with ten order terminals, follow rosids and relatives, which have seventeen, although this is in part because of the unresolved nature of basal relationships within core eudicots.) Of course, the Main Tree could have been drawn with Amborella, Acorus, or a host of other taxa at the far right without offending any relationships; phylogenetic trees are like mobiles, the only fixed points being the nodes. However, pectination, interpreted carefully, has its value. As one reads the terminals of a pectinate tree left to right, adjacent terminals will be separated by a minimum number of apomorphies. When thinking of a book or a herbarium sequence, this would be of some value (see Haston et al. 2007). Nymphaeales and Austrobaileyales are here adjacent on the tree, but they could be separated by hundreds of families in the sequence; 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. (Of course, 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. 2007). This will further help teaching and learning about plants.
In cases where the Angiosperm Phylogeny Group allows alternatives as to the limits of families - Papaveraceae in the broad sense or Papaveraceae plus Pteridophyllaceae + Fumariaceae, Proteaceae in the broad sense or Proteaceae + Platanaceae - the choices made here follow common usage, e.g. as in textbooks like Judd et al. (2002) and Simpson (2006), and particularly in the next edition of Mabberley's The Plant Book (Mabberley 1997) - itself an attempt to reflect a consensus, the result of taking the opinions of botanists at several meetings. For many the existence of alternative classifications will simply confuse, so agreement over which groupings to use when alternatives are permitted seems reasonable. However, I have not yet made all changes that will be needed, e.g. expanding Melastomaceae and Crypteroniaceae.
Higher-level relationships in general, and the composition of orders in particular, have always 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, it is interesting to see that 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, also the "Apomorphies" page here). 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 at all levels.
In many cases the "new" family limits of the Angiosperm Phylogeny Group (see APG 1999, 2003) 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. (Groups like Saxifragaceae s.l., Cornaceae s.l., etc., have long been considered to be unsatisfactory, but until now there has not been compelling evidence to prefer one rearrangement over another.) It is generally accepted that the limits of Lamiaceae and Verbenaceae have to be redrawn, although there is as yet no compelling evidence that the redrawn taxa are not sister taxa (there is no evidence that they are). But whatever their relationships, the content of the clades has changed considerably, and incidentally they are now easier to identify than before; the decision to recognise two families is not difficult. 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 remain difficult around Theaceae (Ericales: see also Sladeniaceae, Pentaphylacaceae) and Euphorbiaceae (Malpighiales: see also Phyllanthaceae, Picrodendraceae, Putranjivaceae, etc.). Here current groupings may not represent quite such dramatic changes in our understanding of relationships. Indeed, parts of the old Euphorbiaceae that were separated may yet go back together (Phyllanthaceae and Picrodendraceae - see Wurdack et al. 2004; Davis et al. 2005), even if recent work (Geuten et al. 2004) suggests that Theaceae indeed should be dismembered. However, given that there is no molecular evidence warranting combining all the Euphorbiaceae segregates, that even if they do come together, the clades the families represent suggest novel groupings not recognised in current classifications, and that Rafflesiaceae appear to be embedded within Euphorbiaceae s. str. (Davis et al. 2007) the family is divided (maintaining a Euphorbiaceae s.l. would entail reducing the iconic Rafflesiaceae to synonymy). Relationships in core Caryophyllales, especially around Phytolaccaceae and Nyctaginaceae and also Cactaceae and Portulacaceae, are incompletely understood and refashioning of taxon limits will doubtless be needed as cladistic relationships become apparent (e.g. see Nyffeler 2007). Some groupings in the old Icacinaceae and Olacaceae remain unclear.
The discovery of the relationships of parasitic and aquatic groups have 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 are hard to place since both the vegetative body and the flowers are changed almost beyond recognition, and plastid gene sequences may be difficult or impossible to obtain, the chloroplast DNA in particular being highly degraded; indeed, rate of molecular change in general may be high (e.g. Duff & Nickrent 1997; Nickrent et al. 1998; Caddick et al. 2002a; G. Petersen et al. 2006b; Barkman et al. 2007). Molecular change may also be rapid and morphological change extensive in sapromycotrophic (Leake 1994) and carnivorous groups. Progress is being made: placements for Rafflesiaceae, Mitrastemonaceae, Cytinaceae and Cynomoriaceae have recently 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 both parts are to be located in Dioscoreales (Merckx et al. 2006), and relationships within the largely hemiparasitic Santalales are also gradually being clarified (Malécot 2002). However, the inclusion of parasitic taxa in general 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). 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, may well be associated with major changes in floral morphology. Here, too, recent molecular studies suggest that aquatic groups with hitherto problematic relationships may find homes. Thus Podostemaceae are in or close to Clusiaceae (Malpighiales: Kita & Kato 2001), Hydatellaceae, which used to be in Poales, are part of Nymphaeales (Saarela et al. 2007), and Hydrostachyaceae have a similar relationship with Hydrangeaceae (Cornales: Xiang et al. 2002); in the first two cases in particular there are morphological and chemical features that support such a move. In general, such groups may show so much molecular change that the problem of long-branch attraction is serious. Unfortunately, given the very different placements of the family, relationships of Ceratophyllaceae remain uncertain. There are also similar morphological problems with many plants pollinated by wind, etc.; again, a variety of characters may be affected.
Given the suggested relationships of such 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. We used to assume that features like highly scalariform vessel perforation plates, a multistaminate androecium or a polypetalous flower were necessarily plesiomorphic, and conversely a simple perforation plate, an oligomerous androecium or a sympetalous corolla were apomorphic. Such assumptions are incorrect. If Podostemaceae are indeed close to Clusiaceae, I look forward to seeing hypotheses to explain how the dramatic changes in the vegetative body that have made Podostemaceae so problematic for generations of systematists took place. That conventional wisdom has trouble in understanding or explaining how the morphologies of groups like Clusiaceae and Podostemaceae can be related is largely a problem with conventional wisdom.
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 [2006] 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 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 means that their users are perhaps more likely to 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. Unless one has a photographic memory, here one has to build up one's knowledge of comparative plant morphology on which 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 56 orders, 445 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 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). 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.
For summaries of apomorphies at all hierarchical levels and of family characterisations, see the Apomorphies page, and for summaries of the sizes of orders and families and of the general arrangement followed in these pages, see the Summary page itself.
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 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). Similarly, the dismemberment of the Icacinaceae and association of fragments once in that family with Aquifoliales and Apiales (see also the circumscriptions in APG 2003, cf. APG 1998) has important effects on the characterisations of those taxa (cf. 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 APG (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 and families such as the old Icacinaceae and Escalloniaceae. A number of these changes seem well supported and have been incorporated in APG II (2003). Elaborations continue, and they are allowing 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 of these characters, I then 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 (reversals excepted) 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. However, I think it rather unlikely that well-supported molecular branches will be overturned by morphological data. Analysis of morphological data alone does suggest 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 [but adding morphological data reduces support for a number of critical clades, too]; Doyle & Endress 2000: however, in none of these papers is the use of morphology without ambiguity - Malcomber & Stevens, ms.). 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). Thus I have been wary of putting much weight on clades that have only morphological support, but note that 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 preferring to fit morphological variation to a tree are mentioned below. Although I may have been mistaken in placing so much emphasis on molecular data in terms of providing the basic phylogenetic framework for angiosperms, morphological data are very rarely in irreconcilably strong conflict with them (Malcomber & Stevens, ms.). However, places where the conflict seems extreme are in the relative positions of the Monimiaceae and Hernandiaceae (Laurales), in the position of Hanguanaceae (Commelinales [as here] or Zingiberales?), and of Triplostegia (is it in Dipsacaceae or Valerianaceae? - see Dipsacales page). 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 extent of the 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), if homoplasious and morphologically indistinguishable from other synapomorphies, at least at the current level of morphological and developmental observation. As mentioned above, orders such as Malpighiales currently have little in the way of morphological support, homoplasious or otherwise, and many nodes with quite strong molecular support within orders like Asparagales lack comparable morphological support.
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 right (i.e., delimited states - or not - 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 Amborellales page), 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 do not suggest family- (or lower) level synapomorphies here, although in the "Apomorphies" page possible synapomorphies at all levels are summarised. If the distributions of these features are compared with those in 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. Myrsinaceae and their relatives, nodal anatomy, etc.; Diapensiaceae, leaf ptyxis; and Peridiscaceae, Centroplacaceae, etc.).
- Secondly, the sampling of nearly all molecular studies is incomplete (see Salisbury & Kim 2001 for problems caused by sampling). But not only is the sampling in molecular studies often less than we might wish, that of the morphological and chemical characters whose evolution we are interested in understanding is also often very poor. So for many anatomical, chemical and embryological characters that are confidently said to characterise families and other groups, we all to 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.
- Thirdly, I am fitting characters to a very conservative tree with many polychotomies, although the nodes that are recognized are for the most part strongly supported with e.g. bootstrap support >80%. 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 state-of-the-art 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 Cotton & Wilson 2007). Of course, some nodes on such fully resolved trees and/or supertrees may have little support, and optimisations based on such trees may carry correspondingly little conviction...
To see the kind of thing that may happen as our knowledge of relationships improves, note the difference between the possible synapomorphies given here for Dipsacales, and those that might remain if [Columelliaceae + Desfontaineaceae] were sister to Dipsacales (see the Dipsacales page). Even in some trees used here for optimisation, parts have poor support, e.g. monocots as sister to eudicots, relationships within aquatic Alismatales, etc.
- 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. 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.
- Finally, 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), we are some way from being able to do this. Many of the states used here are "conventional", descriptors of morphological variation found in the literature sometimes for well over a century, even if in some cases we have since thought about the variation shown by a particular character across all angiosperms. Not only is this inappropriate, but such states often have arbitrary limits, and serve best to communicate "information"; whether they are in fact suitable for either phylogenetic analysis or understanding evolution are separate issues. Thus when interpreting the literature in which character states are optimised on a tree, one should bear in mind all the problems surrounding the delimitation of states. It is not surprising that if the one character is divided into different sets of states, differing ideas of evolution of that character may be the result (e.g., Lamb Frye & Kron 2003; Hibbett 2004).
Unfortunately, but as one might expect, 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). Even these criteria may not yield an unambiguous answer as to what a structure "is", even given a solid phylogeny and an improved understanding of development. As Endress (2005c) recently 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? Maturen et al. (2005) recently 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)...
To summarise, given our current understandings of both phylogenies and characters, 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. Indeed, it has been suggested that for some secondary metabolites in particular there is aquisition of the capability to synthesise a particular metabolite; this is then switched off, but not lost, and so the metabolite is sometimes "reacquired" again (e.g. Wink 2003; Liscombe et al. 2005). Hence the rather spotty distribution of some of these metabolites when considered in the context of phylogenies. In other cases particular phenotypes may be the result of parallel mutations that effect change only because of some previous but as yet undetected change in the larger clade. Whatever the reasons, some characters - and not only those of secondary plant chemistry - seem to come and go on the tree almost willy-nilly.
There are six final caveats about the characterisations:
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 the family, or between the family and its immediate relatives, are unclear. It is unlikely that features so described will turn out to be synapomorphies, although elements of the variation they encompass may. Even in the Apomorphies page some variation is described in this vague fashion.
4. A negative feature of the hierarchical approach, at least as presented here, may seem to be the absence of "biology". 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 groups like Ericaceae are exceptions. Furthermore, much of the "biology" in 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. Indeed, users will add this emphasis as they focus on the biology, morphology, etc., of the taxa that grow locally, although I have been adding details of divergence and/or diversification of clades, particularly striking associations with particular groups of herbivores or pollinators, etc., in succesive versions of this site. In this context, I am reminded of Stebbins's remarks in his dismissive review of Cronquist (1981) which read in their 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).
5. As we find out more about variation we will probably 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.
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 can be questions as to where exactly on the tree a particular fossil is to be placed (e.g., see Nymphaeaceae, Calycanthaceae, 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.
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 mentioned on that page - thus on the Arecales page the update indication is below mention 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. It can be replaced by a reference list of characters that are described under 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" 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.
- "Apomorphies" includes a summary of characters that are possible apomorphies for the various nodes of the phylogenetic trees and for the orders; I am also adding possible family-level synapomorphies. It seemed helpful to include a very brief indication of family size and distribution and also the family characterisations from the order pages. If you click on a family name that is highlighted, you will be taken to that family on the appropriate ordinal page. You can get to the Apomorphies page from any ordinal page by clicking on the highlighted "Apomorphies" immediately after the ordinal name. There is a still much to do on this page (see especially the comments above on the difficulties encountered in delimiting characters and their states and assigning apomorphies to a particular position on the tree), but even in its incomplete state it may be of some help.
- "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 are proliferating notably more than those at lower ranks (Doweld 2001c is a recent example).
- "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 most of the characters used to support the recognition and/or monophyly of a particular taxon; some 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. Once this list is displayed, one can always display the Orders list by choosing the option "Back to Orders" at the beginning of the list.
- "References" is an alphabetical listing of all references cited in this website (it has been broken down into three pages for ease of loading). Clicking on a letter at the top or the bottom of the page will take you to the beginning of those citations whose first author surnames start with that particular letter. 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. This section is made up of three separate, but interlinked, pages. Note that much of the older literature in which there can be invaluable character surveys is coming on line; for example, see the Botanicus Digital Library which will soon be approaching 1,000,000 pages scanned. For a useful device that will provide recent literature, etc., for individual species, see Rod Page's iSpecies.
- "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. Other websites will also be found in the bibliography and in individual ordinal pages.
- "Statistics" is under construction. It has an alphabetical listing of families and their sizes, a list of families with more than 100 species arranged accoding to size, and a summary of the classification used here.
- "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, use Google or iSpecies.
Website Design: The html code and javascript code for the website were generated by hand and by using HomeSite © Allaire/Macromedia Corp. The general design is a three frame set-up, as you can see by looking at the website. The top frame contains the "menu," the side frame contains the "quick reference" lists of orders and characters. The middle frame is the most dynamic and is where most of the pages are displayed. The trees were created by generating a raw dataset in MacClade and drawing the trees in the tree editing window. The tree files were then accessed in PAUP and saved as .pict files to facilitate use in Adobe Illustrator. After polishing the tree images in Illustrator, each tree was saved as a .gif file. Each tree image was made into an image map using a tool in HomeSite, which allows you to select any part of the image (treated as coordinates) and assign a link for those particular coordinates to any place within the website or to any other current website. I imagine there are much faster and much more sophisticated ways of building a website like this, but I am no expert, so I did it the hard way, by trial and error. As the project got more complicated, I figured out how to do each particular feature. If you have any more specific questions regarding design of the website, I can be contacted at hilary.davis@mobot.org.
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 (in Santalales, base of eudicots, base of rosids) 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 topolgies 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), 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 topologies 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. Many studies now use Bayesian analysis; how this will affect our understanding of phylogeny is unclear, but in any event it must be remembered that posterior probabilities for a particular node are usually substantially higher than its bootstrap or jacknife values.
Krell and Cranston (2004) and Crisp and Cook (2005) and others emphasize 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. Furthermore, 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 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.
In connection with this ladderisation of the trees, comments on particular nodes - whether subtending dichotomies or polychotomies - are to be found under the first branch (reading from left to right) on the tree, although there are 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 [CERATOPHYLLALES + CHLORANTHALES + MAGNOLIIDS [MONOCOTS + EUDICOTS]] you will find "ethereal oils +" - this part of the tree seems to be where that feature evolved. However, in the characterisation of Ceratophyllales, of all monocots minus Acorales, and of eudicots you will find "ethereal oils 0". Ethereal oils were subsequently lost several times, as well as being reacquired in Zingiberaceae, within Lamiaceae, etc.
I very largely follow the families and orders recognized by the Angiosperm Phylogeny Group (APG 2003), with modifications suggested by more recent work (see individual pages). Families are grouped within orders as far as possible according to their phylogenetic relationships. I give some ordinal names to families that are unassigned in APG largely for didactic purposes. I have also done things like placing Gunnerales outside the large core eudicot clade to emphasize that they have many characters that may be plesiomorphous and found in taxa both sister to the core eudicots and further basal on the tree, but not the features one usually associates with core eudicots (see D. Soltis et al. 2003).
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 on Reveal's listings (Reveal 2001 onwards) and especially Hoogland and Reveal (2005) and Thorne (with Reveal) 2007. These 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 - indeed, the name of the author of a particular family may dependin on the list consulted. Synonymy is as complete as I can get it at the familial level and above; a few family-level synonyms are unassigned to subfamilies when these are mentioned. A few family or generic names may also be used as headers for groups within families, e.g. Avicenniaceae are within Acanthaceae, and Hydrophyllaceae and Lennoaceae within Boraginaceae; these inconsistencies will be cleared up as phylogenetic patterns become clearer and appropriate nomenclatural proposals are made. Most paraphyletic groups are clearly indicated as being such.
Features are mentioned in the characterisations following the order in the discussion of the characters on the "Characters" page. Possible apomorphies are not indicated, but may be found collected in the "Apomorphies" page. 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 and presence of pericyclic fibers in the stem. In these cases I had initially not considered such characters to be particularly useful (and this indeed may be true of petiole anatomy). Gaps in data are usually indicated, but for many other 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 common in 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, sometimes, as when a generic name is mentioned after a feature, emphasizing that the feature is known from/I know of it from only 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 (some size estimates of infrafamilial taxa have been taken from Thorne 2007). 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 Dictionary (Mabberley 1997) as well as from accounts in Kubitzki (1993 onwards) and Govaerts's checklists (e.g. Govaerts & Frodin 1998). 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 quite 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; some more are still to come. These give only overall indications of natural - i.e. unaffected by recent human activities - distributions, but I have made little attempt to plot the distributions of plants on oceanic islands. In many cases the original maps on which my maps are based have been amended, thus substantial holes in the distributions of many apparently widely-ranging families have become apparent. Indeed, it has proved surprisingly difficult to find accurate maps, although 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 1978, but note that those in Heywood et al. 2007 are more accurate) have been particularly useful. FloraBase (for the flora of West Australia) provides a very useful check for the distribution of plants in that part of the world; would that this were of far wider coverage! I have indicated the sources of the maps where necessary.
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.
Ages of clades are being added, as are comments on mycorrhizal associations, insect groups that feed on the clades, etc. Clade ages at this stage of our knowledge are unreliable, and in several cases there are substantially different estimates for the same event, so please treat these dates with caution.
Infrafamilial classifications for some of the larger families - and trees, where appropriate - are being added as these are being developed.
I have not included much discussion about earlier ideas of relationships or about groupings recognised by extant authors who have classificatory philosophies different from that followed here. Finding out who was "first" in suggesting a particular relationship is not a goal of these pages, the more so since what is often more interesting in such situations is not that a particular suggestion was made, but exactly why it was made. Thus I mention only a few of the many alternative relationships of families and orders that have been suggested in the past, and I certainly have not tried to find the person who was the first to propose a particular relationship. Insofar as I talk about earlier ideas of relationships, I mention largely some suggestions of Cronquist (1981) and Takhtajan (1997), but only because their work is still commonly used. These other systems may follow principles differing substantially from those followed here, e.g. the recognition of paraphyletic taxa may be permitted, also, reasons for prefering the taxa that are recognised are rarely given. (For summaries of commonly used systems, see Brummitt 1992 and Mabberley 2007; examples of the systems are Doweld 2001, Wu et al. 2002, Goldberg 2003, Shipunov 2005, Thorne 2007 [very elaborate classification, useful in part because of Jim Reveal's bibliographic sleuthings], Heywood et al. 2007, 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 it of interest to examine a system recognizing only monophyletic groups; it provides a rather different understanding of evolution.
General referencing is rather minimal in part because of the origin of these notes as a teaching aid, in part because I include very largely references from which I have actually taken information. There may well be additional references on the "Characters" page to general surveys or other sources of information for particular characters, and other references to variation of particular characters within and between families may be found in the discussion after the characterisation of the order. 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). I am finding it useful to change some of the terms used in the earlier versions of the site because I was using terms incorrectly; global changes are being made where appropriate. Building this glossary has also 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. 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!!
v 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 particularly likely in parts of Caryophyllales and Malpighiales. 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 changes are neither a defect of cladistics, nor a necessary consequence of the use of molecular data.
v 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 will 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 will be removed at the same time. Furthermore, this linkage would most readily allow variation to be understood within the context of developing family phylogenies (The importance of having infra-familial variation pegged to its correct level is evident in, for example, Annonaceae [Magnoliales], Convolvulaceae [Solanales], and Fabaceae [Fabales]. Family apomorphies may turn out to be apomorphies for only part of the family.) 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 (in crassinucellate taxa) or the thickness of the integuments could be divided into states after assembling the data on the number of cell layers in these structures in all angiosperm genera. Or not. If variation is fitted to a tree, a preferable course if one is studying morphological change over time (and the approach adopted here as far as possible), 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.
v 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 and still largely are 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.
v Subfamilies or tribes are numbered sequentially within each family. It will be clear that many of the characterisations of subfamilies in particular are only imperfectly worked out. However, some discussion of these groupings is often important, because it clarifies which characters "of" families really are potential synapomorphies and which simply characterise only parts of the family, speciose though those parts may be.
v That I mention some features as not being known is in many cases simply an expression of my ignorance.
v Note that there are one or two unassigned fragments in the text that are unassigned to families (see e.g. the Garryales page) and a few families are not placed in orders.
v This site is updated on a more or less continuous basis. I teach families in the fall [in the spring of 2005!] and this is a particularly good time for finding areas that need attention.
v 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 - peter.stevens@mobot.org should find me.
v 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.
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. However, as with the three delinquent character systems just mentioned, a substantial effort is involved. The main goal for this next year is to tap in to or develop a system that assigns all generic names to their correct APG family.
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.
Version 3.
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.
Version 4.
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 5.
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 6.
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 7.
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 8.
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.