Systematics of Zapoteca (Leguminosae)

Zapoteca (Leguminosae: Mimosoideae)is a relatively well-circumscribed genus belonging to the tribe Ingeae distributed from the southwestern United States and northern Mexico to northern Argentina and the West Indies. The highest concentration of taxa occurs in the dry forests of southern Mexico and, to a lesser extent, in Central America and the northern Andes. The predominance of allopatric distributions and the apparent low frequency of hybrids suggest that speciation in this genus has primarily arisen from genetic differentiation of geographically isolated populations. The recent climatic episodes of the Pleistocene appear to have had a prominent role on the current distributional patterns of Zapoteca species. Zapoteca species have similar reproductive biologies. All probably have nocturnal anthesis and are pollinated by unspecialized settling moths. Self-compatibility appears to be widespread in the genus, Z. tetragona being the only known self-incompatible species. Andromonoecy is another widespread component of the breeding system of Zapoteca species. This probably maximizes the use of reproductive energy without reducing pollinator attraction. The basic chromosome number of Zapoteca (x = 13)and some of the generalized characters of the polyads (i.e., acalymmate, discoid, 16-grained polyads)indicate a relationship between Zapoteca and the remaining genera of the Ingeae, with the exception of Calliandra sensu stricto, which is cytologically and morphologically isolated in this tribe. I recognize 17 species in Zapoteca, three of which (Z. alinae, Z. andina, and Z. tehuana)are newly described. Eleven subspecies are recognized, of which Z. portoricensis subsp. pubicarpa is newly described. A subgeneric classification is proposed, where taxa are grouped into four morphologically distinct subgenera: Nervosa, Zapoteca, Aculeata, and Amazonica. The subgenera are based primarily on differences in vegetative characters: number of pairs of pinnae, number of leaflet pairs per pinna, leaflet size, leaflet texture, venation patterns, and stipule type.