| Euphorbiaceae sensu lato, a large, diverse and economically important family of flowering plants, are here subject to molecular phylogenetic analyses using DNA sequences from six loci. Analyses of plastid rbcL and atpB, along with nuclear small subunit (18 S) sequence data from 80 exemplars of the rosid order Malpighiales, reveal a polyphyletic Euphorbiaceae s. l. and support the recognition of six monophyletic lineages (Euphorbiaceae sensu stricto, Pandaceae, Paradrypetes, Phyllanthaceae, Picrodendraceae, and Putranjivaceae). Relationships of these lineages with the 28 other Malpighiales families are poorly resolved with the exception of a supported sister group relationship between Paradrypetes and the red mangroves (Rhizophoraceae). Further sampling within specific Euphorbiaceae s.l. clades using rbcL (180 taxa), trnL-F region (140 taxa), or ITS (25 taxa) examined finer scale relationships proposed by Webster (1994). Although tribal relationships largely agree with those of Webster, the subfamilies of Euphorbiaceae s.s. must be recircumscribed.;Mitochondrial intron evolution of Malpighiales was also investigated. A nad1-bc intron phylogeny for 60 taxa of Malpighiales is poorly resolved. A proiscuous homing group I intron in cox1 was found to be present in at least 15 families in the order. Putative co-conversion tract differences in the 3' exon adjacent to the site of insertion suggest there are additional cryptic horizontal gains within intron-containing clades. Euphorbiaceae s.s. were identified as the largest known cox1 intron-saturated clade of angiosperms, and incongruence between intron and organismal phylogenies suggests complex patterns of horizontal and vertical transmission and sporadic intron-encoded endonuclease degeneration. Co-conversion evidence is complicated by RNA editing sites and intron-containing taxa that appear to lack co-conversion tracts. The cox1 introns in one clade of Euphorbia (Euphorbiaceae s.s.) contained a 2.1 kb insertion from a portion of the plastid inverted repeat. Phylogenetic analysis of plastid and mitochondrial copies is consistent with one inter-organelle transposition event followed by vertical transmission of this resident insertion with the cox1 intron. |
