Yams and sweet potatoes are in fact two different root vegetables. And unless you shop in a specialty store, it’s likely that you’ve only purchased sweet potatoes, even if they were labeled as yams.
(If you think potatoes are boring, consider the culinary extravaganza of the turducken. What are the birds that get stuffed inside the turkey to make one? Find out here.)
Yams are the tuberous roots of the genus Dioscorea. They are native to parts of Asia and Africa. Yams can grow to weigh over 100 pounds.
The word “yam” is derived, via Portuguese or Spanish, from a West African language called Wolof. The Wolof word nyam means “to sample” or “taste.” Similar words in other African languages for yam mean “to eat” and “to chew.”
Like the yam, the sweet potato is grown for its edible root. But unlike the yam, it is not part of the Dioscoreaceae family. Sweet potatoes are native to South America, and they were the main source of nourishment for early Europeans in the Americas.
So, why do we get them confused?
In general, there are two kinds of sweet potatoes. The firm, white variety was cultivated first in the United States. Once the soft variety was developed for a commercial market, there arose a need to distinguish the two. Because of their resemblance to yams grown in Africa, African slaves in North America had already been referring to sweet potatoes as yams. So, the name stuck.
The U.S. Department of Agriculture tries to help confused consumers by requiring that sweet potatoes labeled “yams” are also labeled sweet potatoes.