Angiosperm phylogeny inferred from 18S rDNA, rbcL, and atpB sequences

A phylogenetic analysis of a combined data set for 560 angiosperms and seve n outgroups based on three genes, 18S rDNA (1855 bp), rbcL (1428 bp), and a tpB (1450 bp) representing a total of 4733 bp is presented. Parsimony analy sis was expedited by use of a new computer program, the RATCHET. Parsimony jackknifing was performed to assess the support of clades. The combination of three data sets for numerous species has resulted in the most highly res olved and strongly supported topology yet obtained for angiosperms. In cont rast to previous analyses based on single genes, much of the spine of the t ree and most of the larger clades receive jackknife support greater than or equal to 50%. Some of the noneudicots form a grade followed by a strongly supported eudicot clade. The early-branching angiosperms are Amborellaceae, Nymphaeaceae, and a clade of Austrobaileyaceae, Illiciaceae, and Schisandr aceae. The remaining noneudicots, except Ceratophyllaceae, form a weakly su pported core cumagnoliid clads comprising six well-supported subclades: Chl oranthaceae, monocots, Winteraceae/Canellaceae, Piperales, Laurales, and Ma gnoliales. Ceratophyllaceae are sister to the eudicots. Within the well-sup ported eudicot clade, the early-diverging eudicots (e.g. Proteales, Ranuncu lales, Trochodendraceae, Sabiaceae) form a grade, followed by the core eudi cots, the monophyly of which is also strongly supported. The core eudicots comprise six well-supported subclades: (1) Berberidopsidaceae/Aextoxicaecae ; (2) Myrothamnaceae/Gunneraceae; (3) Saxifragales, which are the sister to Vitaceae (including Lee a) plus a strongly supported eurosid clade; (4) Sa ntalales; (5) Caryophyllales, to which Dilleniaceae are sister; and (6) an asterid clade. The relationships among these six subclades of core eudicots do not receive strong support. This large data set has also helped place a number of enigmatic angiosperm families, including Podostemaceae, Aphloiac eae, and Ixerbaceae. This analysis further illustrates the tractability of large data sets and supports a recent, phylogenetically based, ordinal-leve l reclassification of the angiosperms based largely, but not exclusively, o n molecular (DNA sequence) data. (C) 2000 The Linnean Society of London.