Yam is available in around 200 different varieties with colors ranging from ivory, yellow to purple. The shape of this tuber is long and cylindrical with a rough exterior. The commercially important species of yam are White Yam, Yellow Yam, Chinese Yam, South East Asian and trifoliate yam. The plant which bears yam is a perennial vine which grows up to 2 meters in length. Yams are quite similar to sweet potatoes but they are no way related it.