Evidentialism factslap: Sweet potatoes aren’t actually potatoes.

Sweet potatoes and common potatoes share part of a name and the spotlight at Thanksgiving meals, but the two are entirely different plants — and sweet potatoes aren’t even potatoes. While both root vegetable species are native to Central and South America, they’re classified as unrelated. Sweet potatoes belong to the Convolvulaceae family, a group of flowering plants that’s also called the morning glory family. Potatoes belong to the nightshade (Solanaceae) family, and are cousins to peppers, tomatoes, and eggplants. 

Both species get their name from an Indigenous Caribbean term, batata, which eventually morphed into the English “potato.” By the 1740s, “sweet” was added to the orange-fleshed tuber’s name to differentiate the two root crops.

Then there are yams. Although they’re often served interchangeably with sweet potatoes at Thanksgiving dinners, this third root crop is biologically unrelated to either sweet potatoes or common potatoes. These tubers belong to the Dioscoreacea family, a group of flowering plants usually cultivated in tropical areas. Luckily, you don’t have to know their scientific classification to distinguish between the two non-spuds at the grocery store: Sweet potatoes have tapered ends and relatively smooth skin, while true yams are generally larger with rough bark and a more cylindrical shape. At most U.S. grocery stores, what you’re seeing labeled as a yam is probably actually a sweet potato.