A new species from Mexico, Dioscorea mesoamericana, is described and illustrated. The new species is distinguished from D. pumicicola by its shorter pistillate inflorescences, the amorphous and geometrically fissured bark on the rhizome, and by the different geographical and altitudinal distri- bution. A key to separate the species, geographical distribution, ecological notes, and a detailed descrip- tion of nervation patterns are given. While reviewing a number of collections at the Gray Herbarium (GH) for the treatment of Dioscoreaceae for the Flora Mesoamericana project during 1987, the senior author found an interesting collection of an undescribed species in fruit from the state of Oaxaca, Mexico. This species was not included in that treatment of the Dioscoreaceae because of the lack of staminate material and because its distri-