Potatoes
The most commonly known stem tuber is the potato. It was cultivated widely in the Americas and was introduced into Spain by Christopher Columbus. A valuable source of carbohydrates, potatoes are popular in the West primarily because they can be grown in temperate climates. Several varieties of potato exist, the most commonly recognized being the white, red and the brown-skinned Russet potato. Potatoes do not cease growth after harvest; shoots will still grow during storage.
Sweet Potatoes
Sweet potatoes are root tubers of a vine plant; they do not generate new shoots and are simply for storage of starch. Orange-flesh sweet potatoes are often incorrectly referred to as "yams" in the United States. Rich in vitamins A, C and beta-carotene, sweet potatoes are grown in tropical and subtropical regions. Also popular are white-fleshed sweet potatoes, known as "boniatos."
Yams
Yams are important, not only as a cash crop but also as a food staple in much of the world. Yams are stem tubers, and come in three main varieties: Great Yams, Yellow Yams and White Yams. Yams are also known as true yams and tropical yams. They are perennial vines and are grown as food almost exclusively in the tropics and subtropics, in particular Asia and Africa. Yams are of the genus Dioscorea, which includes 500 species. Not all tubers of Dioscorea are edible.
Cassava
Cassava is a root tuber and is the most widely cultivated and consumed tuber in the world. Its importance as a source of carbohydrates ranks third after cereal crops such as rice and maize, as it contains 40 percent starch. Originally native to South America, cassava is grown widely in the tropics. Because they spoil quickly after harvesting, cassava is consumed locally, in close proximity to their zones of cultivation.
Taro
Taro, also known as dasheen, eddoe and cocoyam is a plant that originated in Asia and has spread across the entire agricultural world. Its edible tubers are also called "corms," which are regenerative underground stems. It stores nutrition during periods of drought, and is not meant as a long-term supply of food for the plant, as with potatoes. Taro is the source ingredient for the popular Hawaiian dish poi.