Systematics of Vigna subgenus Lasiospron (Leguminosae: Papilionoideae: Phaseolinae)

A taxonomic treatment is herein provided for the six primarily Neotropical species of Vigna subg. Lasiospron. This subgenus is distinguished, in part, by its close relationship with Old World Vigna species, but rather than having an Old World Vigna floral asymmetry where distal floral parts can have a right-hand curvature (from a face-view perspective), distal parts of Vigna subg. Lasiospron flowers, like those of American Phaseolinae, curve to the left. Our proposed taxonomy reflects published phylogenetic analyses that resolve the Vigna subg. Lasiospron species in a subclade of the primarily Old World clade of species of Vigna sensu stricto. Vigna subg. Lasiospron is therefore distinctive in having a primarily neotropical distribution. Three of the six Vigna subg. Lasiospron species have an amphi-Atlantic distribution, which we suggest was achieved naturally by the ability of these species to disperse and colonize coastal habitats. Nomenclatural and taxonomic synonyms are reported, along with species descriptions and the biogeographical, genetic, and morphological evidence that argues for each of the six Vigna subg. Lasiospron species fitting a unified species concept.