The first variety of sweet potato to enter the United States was the white-fleshed one. Later, the orange-fleshed variety was mistakenly referred to as a yam.
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While seemingly a simple question with a simple answer, there's actually a bit of history behind these two, often confused, root vegetables. And, it turns out, most of us living in the United States have probably never had a true yam.
"In the United States there is no difference between a sweet potato and a yam," said Sue Johnson-Langdon, executive director of the North Carolina Sweet Potato Commission. "The term 'yam' has been used to refer to a moist, orange-fleshed sweet potato for a very long time and only legend alludes to its origin," Johnson-Langdon told Life's Little Mysteries. [Sweet Potatoes: Health Benefits & Nutrition Facts]
Sweet potatoes are root vegetables whose skin comes in a range of colors — yellow, orange, red, brown, purple, and beige. And they come in white-fleshed and orange-fleshed varieties.
The white-fleshed sweet potato was the first variety to be consumed in the United States. So when the orange-fleshed variety was introduced to the states several decades ago, producers called them yams (the English form of the African word nyami, which means to eat) to distinguish them from the white variety that was already known as the sweet potato.
Yams are starchy tubers about the size of a small potato that are mostly grown in Africa. They are starchier and dryer than sweet potatoes.
"There is a true yam that is grown in Africa and in South America, but you rarely find true yams in retail supermarkets in the U.S.," Johnson-Langdon said. "The true yam has brown and scaly skin and is either white or cream flesh color."