1627American Journal of Botany 91(10): 1627–1644. 2004.ASURVEY OF TRICOLPATE(EUDICOT)PHYLOGENETICRELATIONSHIPS1WALTERS. JUDD2,4ANDRICHARDG. OLMSTEAD32Department of Botany, University of Florida, Gainesville, Florida 32611 USA; and3Department of Biology, University ofWashington, Seattle, Washington 98195 USAThe phylogenetic structure of the tricolpate clade (or eudicots) is presented through a survey of their major subclades, each of whichis briefly characterized. The tricolpate clade was first recognized in 1989 and has received extensive phylogenetic study. Its majorsubclades, recognized at ordinal and familial ranks, are now apparent. Ordinal and many other suprafamilial clades are briefly diag-nosed, i.e., the putative phenotypic synapomorphies for each major clade of tricolpates are listed, and the support for the monophylyof each clade is assessed, mainly through citation of the pertinent molecular phylogenetic literature. The classification of the AngiospermPhylogeny Group (APG II) expresses the current state of our knowledge of phylogenetic relationships among tricolpates, and manyof the major tricolpate clades can be diagnosed morphologically.Key words: angiosperms; eudicots; tricolpates.Angiosperms traditionally have been divided into two pri-mary groups based on the presence of a single cotyledon(monocotyledons, monocots) or two cotyledons (dicotyledons,dicots). A series of additional diagnostic traits made this di-vision useful and has accounted for the long recognition ofthese groups in flowering plant classifications. However phy-logenetic analyses based on nuclear, plastid, and mitochondrialDNA sequences and morphology do not support this dichot-omy (Donoghue and Doyle, 1989; Olmstead et al., 1992a;Chase et al., 1993; Doyle et al., 1994; Doyle, 1996, 1998;Mathews and Donoghue, 1999; Graham and Olmstead, 2000;Savolainen et al., 2000a; Soltis et al., 2000; Hilu et al., 2003;Zanis et al., 2003). In virtually all published cladistic analyses,the ‘‘dicots’’ form a paraphyletic complex and their diagnosticfeatures are mainly plesiomorphic within angiosperms (seealso Soltis and Soltis, 2004), although the monocots do con-stitute a clade (Chase, 2004).Nonetheless, a large number of species previously consid-ered ‘‘dicots’’ do constitute a well-supported clade: the tricol-pates (Donoghue and Doyle, 1989) or eudicots (Doyle andHotton, 1991). A synapomorphy of the tricolpate clade is pol-len with three apertures (tricolpate/tricolporate pollen and de-rivatives thereof). The tricolpate clade is the largest group ofangiosperms, containing perhaps 165000 species in just over300 families (ca. 64% of angiosperm diversity) and encom-passing phenomenal variation in morphological, anatomical,and biochemical features. The clade also is characterized bycyclic flowers and the presence of differentiated outer and in-ner perianth members (i.e., a calyx and corolla) may be anadditional, albeit homoplasious synapomorphy (Zanis et al.,2003). The staminal filaments are usually slender, bearingwell-differentiated anthers, and most members have S-typeplastids in their sieve elements. This clade was first recognizedin the morphology-based phylogenetic analysis of Donoghueand Doyle (1989). Their monophyly was soon thereafter sup-ported by numerous molecular analyses (Olmstead et al.,1Manuscript received 27 January 2004; revision accepted 4 June 2004.The authors thank Mark Chase, Doug Soltis, and Jeff Palmer, along withtwo anonymous reviewers, for their helpful comments on an earlier versionof this paper. We also thank Darin Penneys and Norris Williams, who assistedin the preparation of the figure.4E-mail: [email protected]; Chase et al., 1993; Doyle et al., 1994; Soltis et al.,1997, 2000, 2003; Ka¨llersjo¨ et al., 1998; Nandi et al., 1998;Hoot et al., 1999; Savolainen et al., 2000a, b; Hilu et al., 2003;Zanis et al., 2003; Kim et al., 2004). This clade was first calledthe tricolpates (Donoghue and Doyle, 1989), but the nameeudicots (Doyle and Hotton, 1991) has gained wider usage.We prefer tricolpates because this name is both descriptive andavoids a connection with the nonmonophyletic assemblage‘‘Dicotyledoneae.’’ Embryos having two (or more) cotyledonsare not synapomorphic for this clade because they are alsocharacteristic of Coniferales, Cycadales, Gnetales, and the bas-al grade of flowering plants from which monocots (which, astheir name implies, share the synapomorphy of a single cot-yledon) and tricolpates are derived.During the past 15 years, our understanding of phylogeneticrelationships within tricolpates has improved dramatically.This has been accomplished largely on the basis of phyloge-netic analysis of molecular data, with many studies represent-ing collaborations of several authors and combining severaldata sets (Chase et al., 1993; Chase and Cox, 1998; Soltis etal., 1998; Hilu et al., 2003). Thus, we now have an accurateoutline (though incomplete in many details) of phylogeneticrelationships within tricolpates (Fig. 1). The classifications ofthe Angiosperm Phylogeny Group (APG, 1998; APG II, 2003)have been based on these ongoing molecular analyses, leadingto the recognition of a series of putatively monophyletic ordersand families. Various secondary criteria, such as strength ofsupport for monophyly, ease of recognition on the basis ofphenotypic features, minimization of taxonomic redundancy,etc., also are used in ranking decisions (APG, 1998; Backlundand Bremer, 1998; Judd et al., 2002; APG II, 2003). The resultis a classification that is phylogenetically accurate, to the ex-tent we can presently determine, and that system is used withsome slight modifications as the basis for the discussion oftricolpate diversity in this paper.Despite tremendous advances in understanding phylogeneticpattern, there is a need for more studies addressing the rela-tionships between morphological characters and phylogenetichypotheses based on DNA sequences (Endress et al., 2000).Studies, such as those of Nandi et al. (1998), Doyle and En-dress (2000), and Zanis et al. (2003) represent an effort, eitherthrough combined analysis or by the mapping of morpholog-1628 [Vol. 91AMERICANJOURNAL OFBOTANYFig. 1. Phylogenetic relationships of major groups of Tricolpates (Eudi-cots); modified from APG II (2003). The names lamiids (for euasterids I) andcampanulids (for euasterids II) were suggested by Bremer et al. (2002). Thenames fabids (for eurosids I) and malvids (for
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