Dioscorea batatas Deene. [Syn. : Dioscorea opposita (Thunb.)] (KASTHALUKA)

Susruta mentioned kasthaluka only once (S.S.Su.46/298) while other samhitas did not mention this plant.  Thakur Balwant Singhji considered it as one of the Dioscorea species. Author identifies it as Dioscorea batatas Deene. [Syn. : Dioscorea opposita(Thunb.)]. Author is also of the opinion that – “most varieties of sweet potato (Ipomoea batatas) are often erroneously termed yams”. The true yams are not grown as food crops, but may be found in tropical areas to a limited extent. In culture and exposure of edible parts yams resemble sweet potato. The sweet potato (Ipomoea batatas) has traditionally been referred to as a “yam” in parts of the southern United States and Canada even though it is not part of the Dioscoreaceae family.

Botanical Description – Dioscorea batatas is a twining herbaceous vine that has an erect,  cylindroid tuber up to 1 m in length. A cross section of the tuber is white when dry. Usually twining in a counter-clockwise direction, stems are purple and glabrous. Simple leaves begin alternately from the lower stems then become opposite farther up the stem. Sometimes the leaves also occur in whorls of three. They are often three-lobed, with the middle lobe being ovate-elliptic to lanceoate, and lateral lobes round to nearly squared, or earlobe-shaped; leaf blades vary from ovate-triangular to broadly ovate or hastate, 3-9 cm long and 2-7 cm broad, with acuminate apices, and deeply to broadly cordate or subtruncate. The plant is a vine with stems reaching 10 to 30 feet, with cordateovate, shiny leaves. It is grown in the tropics for the edible tubers, which develop deep in the ground, so are difficult to dig.

Yam is the common name for some species in the genus Dioscorea (family Dioscoreaceae).These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania. The sweet potato(Ipomoea batatas) has traditionally been referred to as a “yam” in parts of the southern United States and Canada even though it is not part of the Dioscoreaceae family. Yam tubers can grow up to 2.5 meters in length and weigh up to 70 kg. 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.

Major cultivated species

Dioscorea rotunda, the “white yam”, and Dioscorea cayenensis, the “yellow yam”, are native to Africa. They are the most important cultivated yams. In the past they were considered two separate species but most taxonomists now regard them as the same species. There are over 200 cultivated varieties between them.

Dioscorea alata, called “water yam”, “winged yam” and “purple yam”, was first cultivated in Southeast Asia. Although not grown in the same quantities as the African yams, it has the largest distribution world-wide of any cultivated yam, being grown in Asia, the Pacific islands, Africa, and the West Indies (Mignouna 2003). In the United States it has become an invasive species in some Southern states.

Dioscorea opposita, “Chinese yam”, is native to China. The Chinese yam plant is somewhat smaller than the African, with the vines about 3 meters (10 feet) long. It is now grown in China, Korea, and Japan.

Dioscorea bulbifera, the “air potato”, is found in both Africa and Asia, with slight differences between those found in each place. It is a large vine, 6 meters (20 ft) or more in length. It produces tubers; however the bulbils which grow at the base of its leaves are the more important food product. They are about the size of potatoes (hence the name “air potato”).

Dioscorea esculenta, the “lesser yam”, was one of the first yam species cultivated. It is native to Southeast Asia and is the third most commonly cultivated species there. Its vines seldom reach more than 3 meters (10 feet) in length and the tubers are fairly small in most varieties.

D. trifida

Dioscorea trifida, the “cush-cush yam”, is native to the Guyana region of South America and is the most important cultivated New World yam. Since they originated in tropical rain forest conditions their growth cycle is less related to seasonal changes than other yams. These yams are often fertilized with human faeces. Because of their relative ease of cultivation and their good flavor they are considered to have a great potential for increased production (Kay 1987).

Dioscorea dumetorum, the “bitter yam”, is popular as a vegetable in parts of West Africa.

The wild forms are very toxic and are sometimes used to poison animals when mixed with bait (Kay 1987).

Chemical Constituents – Yams are high in Vitamin C, dietary fiber, Vitamin B6, potassium, and manganese; while being low in saturated fat and sodium. Vitamin C, dietary fiber and Vitamin B6 may all promote good health. Furthermore, it is high in potassium and low in sodium hence, likely to produce a good potassium-sodium balance in the human body, and so protect against osteoporosis and heart disease. Having a low level of saturated fat is also helpful for protection against heart disease. Yam products generally have a lower glycemic index than potato products and therefore give better protection against obesity and diabetes.

Botanical Description – The Chinese yam plant is somewhat smaller than the African, with the vines about 3 meters (10 feet) long. It is now grown in China, Korea, and Japan.