In A Nutshell
Although the names are often used interchangeably in the United States, yams and sweet potatoes are from two different families and have varying tastes and textures. The most common type of sweet potato has smooth skin, orange flesh, and a sweet taste, whereas a true yam generally has rough skin, white flesh, and a starchy flavor. Yams are predominantly grown in the tropics and, in the US, most foods labeled as yams are technically sweet potatoes.
The Whole Bushel
Many in the United States wrongly assume yams and sweet potatoes are the same thing when, in reality, they are not even related. In fairness, much of the confusion stems from inaccurate labeling. After all, nearly ever “candied yam” recipe actually calls for sweet potatoes, and many sweet potatoes found in grocery stores are falsely referred to as yams.
So, why do we insist on calling switching the names? Well, there are two common types of sweet potatoes grown in the US: one with white flesh and another with orange. These days, most of us are familiar with the orange variety, but the white sweet potatoes were commercially grown in the US first. When the orange potatoes became popular, people labeled them as yams to differentiate them from the traditional sweet potatoes.
While it might have made more sense to give them a name that didn’t belong to another food, people were already in the habit of calling them yams. African slaves started the trend after realizing the vegetable resembled the yams from Africa.
As it turns out, yams are tubers and sweet potatoes are roots, and they are not botanically related to each other. Yams are more closely related to lilies and grasses and are monocots from the Dioscoreaceae family, whereas sweet potatoes are dicots from the morning glory, or Convolvulacea, family. Also, yams have dark, bark-like skin and are starchier and drier than the soft, moist sweet potato. While both foods come in a range of colors, including purple, white, and orange, the most popular type of sweet potato has orange flesh while yams typically have white flesh. Furthermore, yams are native to Africa and Asia, and sweet potatoes originated from Central and South America.
Although the USDA fully recognizes the difference between the two plants, they allow sellers to use both names on product labels—just as long as the correct name is on there somewhere. Still, real yams are a rarity on US grocery shelves, so if you pick up something that’s packaged as a yam, it’s a fair bet that it’s actually a sweet potato.