Yam is the common name for some plant species in the genus ''Dioscorea'' (family Dioscoreaceae) that form edible tubers.
These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America, the Caribbean and Oceania. There are many cultivars of yam. Although some varieties of sweet potato (''Ipomoea batatas'') are also called ''yam'' in parts of the United States and Canada, sweet potato is not part of the family Dioscoreaceae but belongs in the unrelated morning glory family Convolvulaceae.
== Description ==
Yams are monocots, related to lilies and grasses. Native to Africa and Asia, yam tubers vary in size from that of a small potato to over . There are over 600 varieties of yams and 95 percent of these crops are grown in Africa.〔(【引用サイトリンク】publisher=Library of Congress, United States of America )〕
;Differences between true yam and sweet potato "yam"
Yams are a monocot (a plant having one embryonic seed leaf) and from the Dioscoreaceae family. Sweet Potatoes are a dicot (a plant having two embryonic seed leaves) and are from the Convolvulacea family. They are therefore about as distant as two flowering plants can be. Culinarily, yams are starchier and drier than sweet potatoes. The table below lists some differences between yam and sweet potato.
Yam tubers can grow up to 1.5 meters (4.9 feet) in length〔Huxley, 1992〕 and weigh up to 70 kilograms (154 lb) and 3 to 6 inches high. The vegetable has a rough skin which is difficult to peel, but which softens after heating. The skins vary in color from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the "meat". This substance ranges in color from white or yellow to purple or pink in mature yams.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』