Although sweet potatoes and yams are both flowering plants (angiosperms), they do not have a botanical relationship. Here are some facts from the Library of Congress:
- Sweet potatoes have two embryonic seed leaves (dicot).
- Yams have one embryonic seed leaf (monocot).
- Sweet potatoes come from the Morning Glory family (Convolvulacea).
- Yams come from the Yam family (Dioscoreaceae).
- Sweet potatoes can be either firm or soft. The soft variety is what we call “yams” in the United States.
- Yams are starchier and drier than sweet potatoes and are native to Africa and Asia.
Firm sweet potatoes were introduced in the U.S. before the soft variety. When the soft variety became available, they were called “yams” to differentiate between the two types. Today, the USDA requires that potatoes with the label of “yam” also have “sweet potato” on the label because they are really sweet potatoes and not yams.