What you've been calling a yam is most likely a sweet potato.

Even though cooks use the words yams and sweet potatoes interchangeably,  they're not the same plant at all. Actually, you're unlikely to find a true yam at a grocery store, farmers' market, or restaurant in this country.

With rare exceptions, every orange-fleshed tuber you see or taste in the U.S. — even those sold as candied yams — is a sweet potato. Yams and sweet potatoes aren't even botanical kin. Here's what makes these two so distinct.

Yams vs. Sweet Potatoes

raw sweet potatoes whole and sliced
pile of yams
Left: Sweet Potatoes | Credit: Floortje/Getty Images
Right: Yams | Credit: Zen Rial/Getty Images

What Are Yams, Exactly?

True yams are dry, starchy root vegetables, closer in flavor to yucca than sweet potatoes. They're native to Africa, where 95 percent of yams are grown. They have a bark-like skin and their flesh can be off-white, purple, or red. You're unlikely to find true yams at U.S. supermarkets, but they can be found at some international grocery stores or specialty markets.

What Are Sweet Potatoes?

Sweet potatoes, native to the Americas, are another story. There is tremendous diversity in the sweet potato sector, and growers are constantly adding more heirloom varieties to the mix.

You can find sugary sweet potatoes with snow-white flesh, and purple-fleshed sweet potatoes that taste like nuts. With hundreds of sweet potatoes to explore, finding the variety you like best is part of the fun.

Still, there are a few varieties you're most likely to come across at the grocery store. The sweet potato that most Americans would classify as standard is a Covington, Beauregard, Garnet, or Jewel: It's orange on the inside, mildly sweet, and moist.

Video: All About Sweet Potatoes

Why Are the Words "Yams" and "Sweet Potatoes" Used Interchangeably?

So, if yams aren't typically sold in the U.S., why do we still see the word "yam" appear on labels in grocery stores? According to the Library of Congress, it all comes down to semantics. In the United States, firm varieties of sweet potatoes were the first to be produced. When softer varieties eventually came along, they needed a way to differentiate between the two types. Enslaved Africans had already been referring to soft sweet potato varieties as "yams," because they more closely resembled the yams grown in Africa, and the name stuck.

In an attempt to clear up the confusion, the USDA now requires that labels accompany the term "yam" with the term "sweet potato." For example, the "canned yams" that are often used for making candied yams are actually sweet potatoes, and we know this because the can will say "cut sweet potatoes in syrup." So next time you're at the supermarket and see a vegetable labeled both "yam" and "sweet potato," you'll know that this simply refers to a softer variety of sweet potatoes.