What's the Difference Between Sweet Potatoes and Yams?

Roasted sweet potatoes wedges — Roasted wedges is one way to serve sweet potatoes. It brings out the intense sweet flavor of these diverse tubers. haoliang/Getty Images

If you've ever been confused about yams and sweet potatoes, it's for good reason. The terms are used interchangeably to describe these tuberous root vegetables, even though they're quite different. In fact, they're not even part of the same genus.

There's a reasonable explanation for mix-up. It dates to the 1930s when a researcher at Louisiana State University developed a new type of potato and called it a yam. But that wasn't a yam; it was a sweet potato (more on that in minute).

What Is a Sweet Potato?

Sweet potatoes are tuberous root vegetables that are part of the Convolvulacea or morning glory family. Sweet potatoes are native to South and Central America, but have grown in North America since the mid-1600s.

The most common sweet potato in the U.S. has bright-orange flesh, a brown or reddish skin, and a shape that bulges in the middle and tapers at the ends. Sweet potatoes also can have purple — or even white — flesh.

As the name implies, these tubers are sweet. One of the best ways to prepare them is to roast them because when they caramelize, they become even sweeter. Sweet potatoes also can be served mashed, pureed and of course as fries. They're the main ingredient in one of our favorite Thanksgiving dishes, sweet potato pie.

What Is a Yam?

Like sweet potatoes, yams also are tubers, but they're part of the Dioscorea genus and the Dioscoreaceae family, known for grasses and the lily flower. Yams are native to Africa and Asia and there are more than 600 varieties.

True yams (Dioscorea rotundata) are from West Africa and the term "yam" is the English version of the West African term "nyami" meaning "to eat." Typically, yams have a white, starchy and dry flesh and bark-like skin. The flavor is neutral — not sweet — and is similar to a yuca or russet potato. You might even detect a slight earthy note. True yams aren't very common in the U.S.

Yams are usually prepared steamed or boiled and are often served with braised meat. In West Africa, and throughout the African diaspora, yams are sometimes boiled and pounded into a starchy paste known as fufu.

Why the Name Confusion?

Remember those potatoes developed by the Louisiana grower in the '30s? His name was Julian Miller and his potatoes were a new variety of sweet potatoes (Ipomoea batatas). They were soft with orange flesh and reddish skin and a deliciously sweet taste. These weren't the first sweet potatoes in North America by a long shot, but they were some of the first grown commercially.

Miller and other Southern growers needed a way to distinguish these new soft sweet potatoes from the firm varieties already in production. So they called them yams and well, the name stuck. Today to help minimize the confusion, the U.S. Department of Agriculture (USDA) requires labels with the word "yam" also include the word "sweet potato" because almost all "yams" in the U.S. are sweet potatoes.