BOTANY AND DISTRIBUTION

Several sections have been described under the genus Dioscorea of family Dioscoreaceae. The main food yams have been grouped as follows:

Section Enantiophyllum

This is the largest section with respect to number of species and food importance (Degras 1993). Members may be further grouped in terms of geography as: Asian - Oceanian species, e.g. D. alata L. (water yam, greater yam, white yam), D. glabra Roxb., D. nummularia Lam., D. transversa Br.; Sino-Japanese species (or species complex), e.g. D. japonica Thumb, (igname de Chine, Chinese yam), D. opposita Thumb., and African species or species complex, e.g. D. cayenensis Lam. (yellow yam), D. rotundata Poir. (white Guinea yam, white yam).

Section Lasiophyton

D. pentaphylla L., D. hispida Dennsdest, D. dumetorum (Knuth) Pax (bitter yam)

Section Opsophyton

D. bulbifera L. (aerial yam)

Section Combilium

D. esculenta (Lour.) Burk. (Chinese yam, lesser yam)

Section Macrogynodium

D. trifida L. (cush-cush yam)

The many species of yams (Dioscorea sp.) have various unique or peculiar characteristics that distinguish them from each other. The principal food species have been described in a series of monographs (Martin 1974a, 1974b, 1976; Martin and Degras 1978a, 1978b; Martin and Sadik 1977). Generally the yam plant comprises a shoot portion made up of a vine with branches, leaves and sometimes bulbils in the axils of the leaves, fibrous roots and an underground storage organ, the tuber. The vine twines clockwise or anticlockwise depending on the species.