What is the difference between yams and sweet potatoes?
According to Elizabeth Schneider’s Vegetables from Amaranth to Zucchini (William Morrow, 2001), the orange vegetable that many of us commonly call a yam is in actuality a type of sweet potato (Ipomoea batatas). So is the ivory-fleshed version (also known as Korean, Oriental, or Japanese sweet potato), and so is the boniato-type (a larger sweet potato with fragrant flesh that bakes up dry and fluffy). All sweet potatoes originated in the New World, though many are now grown and used back in Europe and Asia as well.
The true yam has many varieties, all of which originate in the Old World, but which may also be grown and sold here now, particularly in specialty markets. All of the true yams belong to the species Dioscorea, which has 60 edible species (10 of them widely grown). Few of them are sweet; none are as sweet as the orange vegetable we picture with marshmallows at family feasts in the US. Here is a sampling of some true yam types:
- White yam (Dioscorea alata), ñame blanco –“sweet, delicate, mild”
- Purple yam (also Dioscorea alata), ube, ratala, or kand — “gently sweet, with a touch of smokiness, meatiness, and nuttiness”
- Cushcush yam (Dioscorea trifida), mapuey, yampi, or igname couche-couche — “dry, fluffy, and starchy”
- African white yam (Dioscorea rotundata), Guinea yam, Ghana yam, fufu yam — “5 pounds” “potato-like”
- Chinese yam (Dioscorea esculenta), lesser yam, ñame papa “like a fibrous russet”
The following link may also be of interest. Library of Congress explains the confusion between these two types of tubers.