While many orange-fleshed sweet potatoes are thought to be yams or yam sweet potatoes, most likely, they are not true yams. In the United States, almost all types of sweet potatoes, whether the flesh is orange, purple or white, are different cultivars of sweet potatoes.
Yams, from a different family of plant entirely, are dry and starchy. They are imported to the United States from the Caribbean. The confusion between the two names arose when the orange-fleshed sweet potato was introduced to the United States. At the time, producers wanted to distinguish it from the white variety. Farmers used the English version of the African word "nyami," calling the orange sweet potatoes yams.