Euphorbiaceae s.l. are a polyphyletic group containing 5 family-level monophyletic lineages now dispersed in the rosid order Malpighiales. The largest of these lineages is Euphorbiaceae s.s. and includes those Euphorbiaceae s.l. possessing a single ovule per locule (excluding Pandaceae). They comprise 36 tribes, 244 genera, and ca. 6000 species presently classified (sensu Radcliffe-Smith 2001) in subfamilies Acalyphoideae, Crotonoideae, and Euphorbioideae. Phylogenetic analyses of rbcL and trnL-F (trnL intron + trnL-F spacer) DNA sequence data from over 130 taxa resolved intergeneric relationships and identified potential subfamilial clades, although relationships at the highest levels were unresolved. Euphorbioideae were found to form a monophyletic group containing pseudanthial and non-pseudanthial sister clades. Generic delimitation and classification within Euphorbioideae have historically been problematic, especially in tribe Hippomaneae. Our results suggest Hippomaneae are paraphyletic, contain 2 previously unrecognized natural generic groups and that some recent generic splitting is unwarranted. Crotonoideae form 3 unresolved clades including (1) Adenoclineae (with Omphalea), (2) apetalous crotonoids with aperturate pollen and articulated laticifers, and (3) petaliferous crotonoids with inaperturate ‘crotonoid’ pollen. Acalyphoideae are paraphyletic with a small group of Euphorbiaceae s.s. first-branching lineages and a core group that is unresolved with respect to the crotonoid and euphorbioid clades. Major generic re-alignments supported by our analyses would subsume tribes Ampereae, Caryodendreae, Elateriospermeae, Omphaleae, and Pachystromateae and reclassify their constituent genera, as well as, the presently misplaced Dysopsis, Glycydendron, Paracroton, and Sagotia. Our results suggest the need for a new Euphorbiaceae s.s. infrafamilial classification involving 5-8 subfamilies and additional significant tribal recircumscription of crotonoids.

Key words: Euphorbiaceae, phylogeny, rbcL, re-classification, trnL-F