Yams are native plants of Africa and Asia and belong to the Dioscoreaceae family of roots and tubers. There are more than 600 varieties of yams, and 95 percent of them grow in Africa. These starchy vegetables are often confused with sweet potatoes in the United States.
Yams and other tubers entered America during the Portuguese slave trade with Africa in the 1500s. The Americanized term for the plant comes from the African word nyami. These tubers became an important food staple in Caribbean countries once African slaves brought them to the new world.
Yams are around the same size as normal potatoes. These ancient plants were first known to humans around 50,000 B.C. Yams grow year-round in tropical biomes. Most of the United States' crop of true yams come to the country as imports from tropical nations in the Caribbean. According to the Library of Congress, the U.S. Department of Agriculture requires labels with the term "yam" to also include the term "sweet potato."
Yams are drier and contain more starch than sweet potatoes. The yam is a monocot, meaning the plant has one embryonic seed leaf and is closely related to lilies and grasses. Sweet potatoes have two embryonic seed leaves and are in the same family as morning glories.