Classification

The eudicots contain 75 percent of all angiosperms, or about 165,000 species distributed among roughly 300 families. The eudicots include all the familiar angiosperm trees and shrubs and many herbaceous groups. Some of the larger, better-known families of eudicots include Rosaceae (rose family), Fabaceae (bean family), Brassicaceae (mustard family), Ranunculaceae (buttercup family),

Apiaceae (parsley family), Asteraceae (sunflower family), and Lamiaceae (mint family). The eudicots include many familiar trees, such as those of the Fagaceae (oak or beech family), Betulaceae (birch family), Juglandaceae (walnut or hickory family), Aceraceae (maple family), and Platanaceae (plane tree or sycamore family).

A good understanding of the major groups of eudicots has emerged from the use of DNA sequence data. The early-diverging eudicots consist of a number of ancient lineages, including Ranun-culales, a group containing the Ranunculaceae and Papaveraceae (poppy family). Other early-diverging eudicots include Buxaceae (boxwood family) and Proteales; the latter includes the Platanaceae and Pro-teaceae (sycamore and protea families).

Following the early-diverging eudicots is a large clade, referred to as the core eudicots, that contains most eucidots. The core eudicots consist of three major clades (rosids, asterids, and Caryophyllales) and several smaller ones (Santalales, Saxifragales, and Gunnerales). The rosids and asterids are very large groups, each containing roughly one-third of all angiosperms. Traditional classifications, such as presented by botanist Arthur Cronquist in 1981, do not reflect modern views of phylogenetic relationships. For comparison, the rosid clade now recognized is made up of members of the traditional subclasses Rosidae, Dilleniidae, and Asteridae (in the sense of Cronquist, 1981); the asterid clade contains members of subclasses Asteridae, Dilleniidae, and Rosidae; and Caryophyllales contains taxa previously placed in Caropyllidae and Dilleniidae.

Relationships among the core eudicots are still unclear, despite intensive study using DNA sequence data. The difficulty in clearly describing relationships among these groups appears to stem from the fact that following the origin and initial diversification of the eudicots, a rapid radiation (evolution of many organisms in a short period of time) occurred, yielding the groups of core eudicots seen today.

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