Are sweet potatoes and yams the same?

In the U.S., there is often much confusion between sweet potatoes and yams. They are completely different foods, belonging to different plant families. Sweet potatoes are much more highly available in the U.S. than are yams.

This confusion exists for two reasons. First, as a shopper, it is possible for you to find sweet potatoes and yams that look reasonably alike in terms of size, skin color, and flesh color. Second, government agencies have allowed these terms to be used somewhat interchangeably on labeling, so that you often cannot rely on the grocery store signs to help you determine whether you are looking at a bin full of sweet potatoes or a bin full of yams. For example, in many stores you can find bins that are labeled “Red Garnet Yams” and “Jewel Yams” and the foods in these bins are actually sweet potatoes. Here are some general practical rules that you can follow.

• In most U.S. groceries, you should assume that you are always purchasing a sweet potato, even if the sign says “yams.” Over 1 million sweet potatoes are commercially grown in the U.S. each year, while commercial production of yams in the U.S. is rare.
• Don’t use flesh color to decide whether you are getting a sweet potato or a yam. Both root vegetables come in a variety of colors. Once again, you should assume that you are getting a sweet potato regardless of flesh color.
• If you are specially seeking a true yam (from the plant genus Dioscorea), it might be helpful to visit a more internationally focused store that specializes in foods from tropical countries.

Here is a little more background about the relationship between sweet potatoes and yams.

The name “yam” was adopted from “nyami”—the Fulani (West African) word that means “to eat” and that has traditionally been used to refer to yams. Yams are native to Africa and Asia, and unlike potatoes, they have the potential to grow to a much larger size.

From a science perspective, true yam is a root vegetable belonging to the Dioscoreaceae family, which are monocotyledons (or “monocots” for short, with the prefix “mono” referring to the fact that they have only one embryonic seed leaf). Sweet potatoes belong to the Convolvulaceae or morning glory plant family, are dicotyledons (or “dicots” for short, with the prefix “di” referring to the fact that they have two embryonic seed leaves), and are known by the scientific name of Ipomoea batatas. So, as you can see, these two root vegetables come from very different parts of the plant world, even though their names have become so intertwined in the U.S. marketplace.