African yam bean ( Sphenostylis stenocarpa (Hoechst ex. A. Rich.) Harms.)

The African yam bean belongs to the family Leguminosae (Fabaceae), an annual, climbing or prostrate vine. The botany of the crop has been described (Okigbo, 1973; Duke, 1981). The vine produces linear pods, 20–30 cm long in which 20–30 seeds are borne. The seeds are usually brown, cream, orange-brown or mottled and ovoid in shape. The yam bean is usually interplanted with yams and other vegetables in the traditional village farm setting. According to Ezueh (1984) flowering occurs 80–130 days after planting and seed maturity after 150–300 days. Seed yield is very poor in Nigeria, about 300–500 kg/ha (Ezueh, 1984) although much higher estimates of yield (2000–3000 kg/ha) have been reported for fertile soils (NAS, 1979). Tuber yields of 100–300 g/plant are common, with hectare yields estimated at about 2000 kg (NAS, 1979), also in fertile soils. The African yam bean flourishes all through tropical Africa, where both seed and tuber are important components of the diet. However, it is not well known as a food source outside Africa and is grown as an ornamental plant in Europe and elsewhere. It is distinct from the Mexican yam bean or simply yam bean, which grows extensively in Central and South America, primarily Mexico and Brazil. The Mexican yam bean is a tuberous vine, grown mainly for the delicious tuber, but not for the seeds, which are toxic.