Yams
Family Dioscoreaceae
Dioscorea sp., yams (D. sp 1), are dioecious perennial plants with small green flowers in axillary inflorescences (D. sp 2), cultivated for their starch containing edible tubers.
The genus Dioscorea is named after Pedacius Dioscorides, an ancient Greek physician from the time of Nero, writer of the De Materia Medica.
The top of the tuber produces an annual stem that climbs by twinning for several meters (D. sp 3), (D. sp 4), (D. sp 5). The tubers vary is size, shape and colour (D. sp 6), (D. sp 7), (D. sp 8). Usually one cylindrical tuber is produced (D. sp 9), but lobed, branched or flattened tubers occur. The suberized skin and flesh vary in colour from white to purple. The composition of the tuber resembles the potato.
Distribution
All but one of the yams are of Old World origin. Only Dioscorea trifida, cush-cush yam (D. sp 10) is of American origin and is cultivated in the West Indies. Most species are essentially tropical. There are two areas of the tropics where yams are most important in the diet: the wet part of West Africa, where Dioscorea rotundifolia, white yam, and Dioscorea cayenensis, yellow or Guinea yam, occur; and Southwest Asia, where Dioscorea alata, Asiatic or greater yam (D. sp 11) is the most important yam with the highest yield of all yam-species. It spread in early times from Southeast Asia to New Guinea and Polynesia. Later it was taken to Madagascar and from there to the East African coast. In the 16th century it reached West Africa and the New World. The second most important species, in this and several other areas, is Dioscorea esculenta, Chinese or lesser yam. It was already cultivated in China in the 3rd century AD. It is not widely grown outside Asia and the Pacific.
Some less important species are Dioscorea bulbifera, potato or aerial yam (D. sp 12), in which aerial bulbils are produced in the leaf axils and subterranean tubers are much reduced; Dioscorea opposita (D. sp 13), a Chinese yam which tolerates a cooler climate and was introduced experimentally in Europe in the 19th century as a substitute for potatoes; and Dioscorea hispida, Asiatic bitter yam (D. sp 14), with toxic tubers used for hunting.
Use
Yams were used for ship’s stores as they are easy to handle, can be stored for a long period, and are fairly rich in vitamin C. On slave ships they were the main source of food.
The peeled yams may be boiled, roasted or fried in oil. In West Africa they are pounded and eaten as fufu. Yams also play an important role in the socio-religious life in West Africa.