Yam  large, sub-aerial soft starchy, tuberous root of any of various climbing vines of the genus Dioscorea, having about 600 species under the family Dioscoreaceae. There are about 11-12 cultivated species in the tropical and subtropical regions. The most common cultivated specie are D. alata, D. rotunda, D. opposita, D. cayenansis and D. esculanta. Yam is the chief food of millions of people in West India, South Afiica, Central Africa and tropical Asia. In Bangladesh D. alata has the largest yield; average yield per plant is about 8 kg.; flesh is white or cream coloured and may even be pink or purple. D. esculanta is a smaller palatable yam also cultivated in some places. They are cultivated in April or May by cutting the tuber having one or two young stem bud. In Bangladesh it is cultivated mainly as homestead plant and consumed as vegetable. The wild species are not exploited for either food or for any steroidal sapogenins related to sex hormones or cortico-steriods. [Mostafa Kamal Pasha]