With Thanksgiving coming up, I’ve been thinking about a confusing situation: the difference between yams and sweet potatoes. At the grocery store recently, I saw root vegetables with orange flesh and brown skin (which I’ve always known as sweet potatoes) identified as yams. Next to them, similar root vegetables with purple skin and white flesh were called sweet potatoes.

This was surprising, and I had a big discussion with my family around the dinner table (including taste-testing the orange-flesh “yams” and the white-flesh “sweet potatoes” — we liked the orange-flesh better for its sweetness and soft texture).

Then, a few days later, at another grocery store, these two same food items were both labeled yams, with U.S. origin. The produce manager told me the two terms were used synonymously. In common usage, that’s obviously true, but I was pretty that I’d once read that the two foods were different. I checked in the World Book Encyclopedia, yams and sweet potatoes are indeed completely separate plant species. Yams only grow in tropical climates and are not produced in the U.S.

It’s not just a vocabulary question. It’s also a cultural question. In many African countries, yams are a basic staple. I subtitled a French-language film recently that took place in Benin, and one character brought groceries to someone who had run out of money: the items were rice, bottled water, and yams. Yams are also used to make a kind of flour. So they are pretty important traditionally and in daily life in that part of the world. Sweet potatoes can be delicious, but they don’t play nearly as important a role in American culture (though they are Thanksgiving classics, with or without marshmallows — but that’s another debate).

The North Carolina Sweet Potatoes website explains that “what you’ve been calling a yam is most likely a sweet potato. Even more, it’s possible that you’ve never even tasted a yam!” There are many kinds of sweet potatoes, and the white-flesh variety used to be more common in the U.S. When the soft, orange-flesh variety started to be grown, producers decided to call them “yams” to distinguish them from the typical white-flesh sweet potatoes. This is because, according to the Library of Congress website, African slaves had already been calling these vegetables “yams” because they reminded them of the yams they ate back home. So, if Africans hadn’t been brought over to the U.S. as slaves, we wouldn’t call sweet potatoes yams. The West African word gave rise to Portuguese “inhame,” French “igname,” and English “yam.” Interestingly, according to Merriam-Webster the word is related to Fulani “nyami,” which means “to eat.” You know a food must be a true staple when its name is related to the verb that means “to eat”!