Yam

Yam is the common name for some plant species in the genus Dioscorea that form edible tubers (some other species in the genus being toxic). Yams are perennial herbaceous vines native to Africa, Asia, and the Americas and cultivated for the consumption of their starchy tubers in many temperate and tropical regions. The tubers themselves, also called "yams", come in a variety of forms owing to numerous cultivars and related species.

Source: Wikipedia