Guinea yam (Dioscorea cayenensis Lamk. and D. rotundata Poir), a staple root crop in the west tropical Africa, accounts for the largest share of the world yam production. Despite its economical and cultural importance in the region, its taxonomy has been confusing, and little is known about its phylogeny. In this paper, the history of Guinea yam classification is overviewed. The enormous diversity of wild relatives of Guinea yam is described and discussed with regard to their habitats (rain forest vs. savanna) and the selection of the shape of the storage organ by animal predators. New insights into Guinea yam phylogeny are presented on the basis of the chloroplast DNA and nuclear ribosomal DNA analysis.