The sweet potato (Ipomoea batatas) is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet tasting tuberous roots are an important root vegetable (Purseglove, 1991; Woolfe, 1992). The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally, but many are actually poisonous. The sweet potato is only distantly related to the potato.
The softer, orange variety is often called a yam in parts of North America, a practice intended to differentiate it from the firmer, white variety. The sweet potato is botanically very distinct from the other vegetable called a yam, which is native to Africa and Asia and belongs to the monocot family Dioscoreaceae. To prevent confusion, the United States Department of Agriculture requires that sweet potatoes labeled as "yams" also be labeled as "sweet potatoes".
In 1992, the Center for Science in the Public Interest compared the nutritional value of sweet potatoes to other vegetables. Considering fibre content, complex carbohydrates, protein, vitamins A and C, iron, and calcium, the sweet potato ranked highest in nutritional value. According to these criteria, sweet potatoes earned 184 points, 100 points over the next on the list, the common potato.(NCSPC)
Sweet potato varieties with dark orange flesh have more beta carotene than those with light coloured flesh, and their increased cultivation is being encouraged in Africa, where vitamin A deficiency is a serious health problem. Despite the name "sweet", it may be a beneficial food for diabetics, as preliminary studies on animals have revealed that it helps to stabilize blood sugar levels and to lower insulin resistance.
Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta carotene (a vitamin A equivalent nutrient), vitamin C, and vitamin B6. Pink, yellow and green varieties are high in carotene, the precursor of vitamin A.
Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most important product. In some tropical areas, they are a staple food-crop.