Yams
Yams are classsified as Dioscorea trifida; D. alata; D. esculenta; D. rotundata; D. cayensis.

This thick, tropical-vine tuber is popular in South and Central America, the West Indies and parts of Asia and Africa. Although sweet potatoes and yams are similar in many ways and therefore often confused with one another, they are from different plant species. Depending on the variety, a yam's flesh may be various shades of off-white, yellow, purple or pink, and the skin from off-white to dark brown. The texture of this vegetable can range from moist and tender to coarse, dry and mealy. There are over 150 species of yam grown throughout the world. They can range in size from that of a small potato to behemoths over 7 1/2 feet long and 120 pounds.

Though they can be similar in size and shape to sweet potatoes, yams contain more natural sugar and have a higher moisture content. On the downside, they're not as rich in vitamins A and C as sweet potatoes.