What's the difference between a yam and a sweet potato?

“I just bought a sweet potato and it was white on the inside. Does that mean the orange ones are yams? What’s the difference?”

The North Carolina Sweet Potato Commission quickly set the record straight. Sweet potatoes can have orange, white, or purple flesh, and, though the orange ones are often called yams, true yams are a different species of plant altogether. The North Carolina Agricultural and Technical State University put together a chart listing the differences. Sweet potatoes are dicots and they’re part of the morning glory family. They originated in South America but can be grown in the United States. Yams, on the other hand, are monocots, part of the genus Dioscorea, and mostly imported from the Caribbean. They originated in Asia and West Africa.

According to Cooking the West African Way by Bertha Vining Montgomery and Constance Nabwire, yams are a staple in West African cooking. They figure into the culture as well and are the focus of harvest festivals like the Iri-Ji (or “new yam”) Festival. 

Unless you’ve gone to a specialty restaurant or grocery store, you may never have eaten a genuine yam. Look closely: the FDA requires sweet potatoes to be labeled as such, and even the cans of candied yams are inscribed with “sweet potato” in small text.