Yams vs. Sweet Potatoes

A sweet potato is not a yam. A yam is not a sweet potato. A sweet potato is not a potato, nor is a yam. The US FDA, which regulates food labeling, does not have a standard of identity for either sweet potatoes or yams, so either term works. The US Department of Agriculture requires that labels with the word ‘yam’ on them also be accompanied by ‘sweet potato’.

They are both tuberous root vegetables that come from a flowering plant. The sweet potato is in the morning glory family, while yams are related to palms and grasses.
Yams are starchy and dry. Sweet potatoes are sweet and moist, some more than others.

Some yams and some sweet potatoes look similar. They are both tubers or edible roots.

Shape is the key. Sweet potato can be short and fat or long and thin, but it will always taper at the ends. Yams have a cylindrical shape with blackish or brown, bark-like skin and white, purple, or reddish flesh. Yams can be reddish or purplish as well, but most often, if you scrape the skin with a fingernail, you see white or cream-colored flesh. Most Americans have never had a real yam.

Sweet potatoes are grown in the United States, mainly North Carolina. Yams in Africa (where they originated), Southeast Asia, the Caribbean, and Central America.
Since the "soft" sweet potatoes slightly resembled true yams, they picked up the name and became labeled as "yams" in most US grocery stores. Common US Grocery Store Labeling
 Yam — Soft sweet potato with a copper skin and deep orange flesh.
 Sweet potato — Firm sweet potato with golden skin and lighter flesh.

A yam is super sweet and can grow over seven feet in length. Yams are toxic when eaten raw, but safe when cooked. A true yam is a starchy edible root of the Dioscorea genus. It is rough and scaly and very low in beta carotene.