Although both sweet potatoes and yams are tubers, or root vegetables, they are two very different vegetables. In fact, the two vegetables even belong to two different plant families.
The interchangeable use of the term “yam” for both vegetables in the past has led to a great deal of confusion. Below is a brief description of each vegetable, how they are used, and where they can be purchased.
What are Yams?
Yams are a vegetable belonging to the genus Dioscorea and are native to West Africa and Asia. This root vegetable is long, cylindrical, has rough, scaly skin and a light colored flesh. The flesh tends to be dry and starchy and must be cooked prior to eating. Yams can grow up to five feet long and weigh up to 150 pounds.
Yams are an important staple food in many parts of Africa, where they are most often boiled, fried or roasted. The ability of yams to be stored for up to six months at a time allows for a dependable food source during rainy seasons or other poor growing conditions. It is for this reason that yams have become a prominent staple food in this region of the world.
In Asia, purple yams are popular and often used in desserts. Purple yams are a common ingredient found in the Philippines, Vietnam, Indonesia, and Japan.
In the United States, where yams are not commonly consumed, most major grocery stores and supermarkets do not carry them. Yams can be found in specialty markets and ethnic markets, especially those specializing in African, Asian, or Caribbean cuisine.
What are Sweet Potatoes?
Sweet potatoes are a plant belonging to the genus Ipomoea and part of the same family as Morning Glories. These vegetables are usually short and fat with tapered ends and a smooth, brightly colored skin. The skin and flesh can range in color from beige to the more popular orange or even deep purple. Although the flesh is fairly starchy, it is sweeter and more moist than yams. The sweet potato is thought to have originated in Central or South America but is now cultivated vastly across the globe, even in Hawaii and New Zealand.
Because of the sweet potato’s unique combination of starchy sweetness, it can be used for a variety of dishes, both savory and sweet. In the United States, sweet potatoes are often baked, mashed, or fried. Due to its starchy nature, sweet potato puree can be mixed into a variety of recipes such as soups, baked goods, or desserts. Sweet potatoes have, over the years, become a traditional part of the Thanksgiving meal.
Sweet potatoes can be purchased in most major supermarkets in the United States, year round. Sweet potatoes generally undergo a curing process after harvest, which increases their storage time to up to 13 months. Pre-peeled and cooked sweet potatoes can also be purchased canned or frozen.
How the Confusion Began
The first reference of the term “sweet potato” was in the Oxford English Dictionary of 1775, although it is not clear which exact species this referred to. When the soft-fleshed variety of sweet potato began to be cultivated in the southern United States, African slaves who thought the vegetable resembled the yams grown in Africa began calling the sweet potatoes yams. Since that time, the word "yam" has been commonly used for the sweet potato.
To prevent further confusion between the two vegetables, the United States Department of Agriculture now requires that all sweet potatoes labeled with the name “yam” must also be labeled with the term “sweet potato.”