Yams and Sweet Potatoes

Yams and sweet potatoes taste more-or-less like each other, but they have little else in common. Sweet potatoes are botanically very distinct from yams. Sweet potatoes are members of the morning glory family, whereas yams are tubers of tropical vines that are closely related to lilies and grasses. Sweet potatoes are native to Central and South America, whereas yams are native to Africa and Asia. Sweet potatoes are dicotyledons; yams are monocotyledons.

If you live in North America, unless you specifically search for yams, you are probably eating sweet potatoes. It is not unlikely that you have never even tasted an actual yam. Yams are popular in Latin American and Caribbean markets; they are slowly becoming more common in U. S. markets.

Sweet potatoes are of two dominant types. One type has a thin, light yellow skin with pale yellow flesh that is not sweet, and it has a dry, crumbly texture. The second type is the one that is most often incorrectly called a yam. It has a thicker, dark orange-to-reddish skin with a vivid orange, sweet flesh and a moist texture.

Yams contain more natural sugar than sweet potatoes and thus are generally sweeter. However, yams are much starchier than sweet potatoes and not nearly as nutritious. Sweet potatoes are packed with vitamin A, which is considered critical in maintaining proper eye health. One sweet potato contains nearly eight times an adult's daily need of Vitamin A, and, because the vitamin is fat-soluble, the body can store it for later use.

Sweet potatoes contain several other vitamins and minerals in amounts not found in yams. Sweet potatoes contain significantly higher amounts of calcium, iron, and vitamin E, and twice as much protein per serving. Sweet potatoes are also strong sources of beta-carotene, manganese, and copper. Sweet potato varieties are classified as either “firm” or “soft”. When cooked, those in the firm category remain firm, whereas soft varieties, although actually firm when raw, become soft when cooked.

It is the soft varieties that are often (incorrectly) labeled as yams in the U. S. Firm varieties of sweet potatoes were produced in the U. S. before soft varieties. When soft varieties were first grown commercially, there was a need to differentiate between the two. African slaves called the soft sweet potatoes yams, because they resembled the yams in Africa. Thus, soft sweet potatoes were referred to as yams to distinguish them from the firm varieties of sweet potatoes. The U. S. Department of Agriculture requires sweet potatoes that are labeled as yams to also be labeled as sweet potatoes.