Yams are tropical by nature and should not be confused horticulturally with the sweet potato.
Yams belong to several genera including Dioscorea.
Fleshy, moist sweet potatoes, mainly from Louisiana, have been misnamed as yam. Boniatos are a type of sweet potato, commonly referred to as Cuban Sweet Potato, though they are tropic in origin and look more like a yam. User support of VU is appreciated.