Eudicots

Abstract Much attention and effort have been devoted to the understanding of the early evolution of eudicots, a group comprising a large proportion of the angiosperm total species number (75%, 1). 7ey are characterized by the presence of tricolpate pollen grains (or derived from this type), a type of pollen grain with three pores set in apertures called colpi (Fig. 1). Eudicot taxa at the basal nodes of the tree consist of several small to medium-sized lineages in which the two most important groups of angiosperms, rosids and asterids, are nested. thesetwo groups account for almost two-thirds of all angiosperm species (88% of eudicot species; 1). In this chapter, relationships and divergence time estimates of early-diverging eudicots as well as the smaller lineages of core eudicots are reviewed. therosid and asterid groups are discussed elsewhere in this volume. Ranunculales is the Arst diverging group in eudicots, followed successively by Proteales, Sabiaceae, Buxaceae + Didymelaceae, and Trochodendraceae (2–6). Relationships in this sequence are not well supported, and other studies have proposed slightly diBerent topologies (7–9). theremainder of the eudicots form a group principally characterized by strong support in various molecular phylogenetic analyses and has been labeled “core eudicots” (10).