Yams

Yams are not a type of potato. Both are stem tubers that grow underground, but they belong to different botanical families. The potato is a part of the nightshade family, which also includes peppers and tomatoes. Yams belong to a plant family of flowering vines that surprisingly includes grasses and lilies. 

Compared to sweet potatoes, yams have an earthy, neutral taste. They can be mildly sweet but mostly take on the flavor of the seasonings used in the dish.