Are sweet potatoes the same as yams? No. . . and yes. Here's the scoop.
Literally and botanically speaking, the two are not related.
- Yams are big tuberous roots that are a monocot (a plant having one embryonic seed leaf) and belong to the genus Dioscorea. They are related to grasses and lilies, growing in tropical and subtropical countries that provide eight to ten months of warm weather to mature. Yams can grow two to three feet long and some can weigh as much as 80 pounds. According to horticulturist U. P. Hedrick, the word yam means "to eat" in the dialect of Guinea.
- Sweet potatoes are a dicot (a plant having two embryonic seed leaves) and are from the Convolvulacea or morning glory family. In the United States today it is possible to find true yams in some urban Hispanic markets. However, most yams in the U.S. are actually sweetpotatoes with relatively moist texture and orange flesh. Compared to sweet potatoes, yams are starchier and drier.
Both the yam and the sweet potato DO grow underground and have yellowish-orange flesh, but there the similarity ends. Yet the two became entwined in this country by household vernacular in part through the work of a publicity campaign. Earlier this century, sweet potato promoters attached the word yam to the deep orange, moist-fleshed varieties of sweet potatoes and left the words sweet potato to the smaller, yellowish, and drier-fleshed varieties.
The two types of sweet potato are interchangeable in cooking, but bring different tastes, textures, and colors to your plate. Centennial and Puerto Rico are two popular moist-fleshed (formerly called yam) varieties; Nemagold, New Jersey Orange, and Nugget have the lighter and drier (sweet potato) flesh.
Today it is common to find either or both words used in supermarkets, although sweet potato promoters wish we would all stop saying yam. The North Carolina SweetPotato Commission currently urges the world to spell "sweetpotato" as one word. But it's an uphill battle. If your Mama called them yams, for certain you will, too.