CHLOROPLAST DNA PHYLOGENETIC STUDIES IN NEW-WORLD PHASEOLINAE (LEGUMINOSAE, PAPILIONOIDEAE, PHASEOLEAE)

Chloroplast DNA restriction site variation was examined in several species of Phaseolus, Vigna, and Ramirezella, and in four potential outgroups (Dipogon, Macroptilium, Oxyrhynchus and Strophostyles) of the Phaseolus-Vigna complex. Cladistic analyses of restriction site characters yielded 22 equally parsimonious trees with a consistency index of 0.60. Results of the chloroplast DNA analysis are consistent with current hypotheses from morphological studies in suggesting that Phaseolus is monophyletic, but that Vigna is polyphyletic. The Vigna plastomes are divided into two clades. One consists of all the Old World subgenera surveyed and the New World subg. Lasiospron, supporting morphological evidence that this distinct New World subgenus may be more closely related to the Old World groups than to other New World subgenera. The second clade is strictly New World and comprises Vigna subg. Sigmoidotropis, V. populnea, Ramirezella and Oxyrhynchus. The close relationship of Ramirezella chloroplast DNA's with New World Vigna and Oxyrhynchus plastomes follows recent cladistic analyses of morphological characters. Relationships of plastomes of the New World clade to the mostly Old World Vigna clade depends on rooting of the tree. Within Phaseolus, species from three small and distinct Mexican endemic sections have monophyletic chloroplast DNA's. Plastomes of the larger sect. Phaseolus are not monophyletic, but subgroups within the section follow relationships proposed by non-molecular studies. If rooted with Dipogon, the chloroplast DNA gene tree places Phaseolus, along with Macroptilium and Strophostyles, as sister group to the New World Vigna clade. Otherwise, if rooted with the Macroptilium and Strophostyles plastomes, Phaseolus chloroplast DNA's are sister group to plastomes of both Vigna clades and of Dipogon.