TAXONOMY, CONSERVATION AND SUSTAINABLE UTILISATION OF THE GENUS DIOSCOREA IN WESTERN GHATS Elsamma Joseph Arackal 1 and A.G. Pandurangan 2. 1. Maharajas College, Ernakulam, Kerala - 682011 2.Jawaharlal Nehru Tropical Botanic Garden and Research Insti

Abstract

The genus Dioscorea L. is one of the largest groups among monocotyledons belonging to the family of Dioscoreacese in the natural order Dioscoreals (Ayensu, 1972). The genus has about 850 species in the world (Mabberley 1997) and distributed mainly in 3 centres of diversity namely South Africa, South East Asia and Latin America. The members are commonly known as “yams†and are widely cultivated for its edible tubers throughout the tropics occupies third position as most important food crops in the world next to cereals and pulses. They are mainly represented by herbaceous twinning climbers which lack tendrils. They usually inhabit in forest margins and more open habitats and distributed up to 3500 m above MSL. The aerial stem twines on the neighbouring vegetation and sometimes possesses prickles. The leaves are with variable phyllotaxy and are distinctly petiolate. Bulbils are also present in many of the species. The plants are usually dioecious and the inflorescences are axillary spikes with actinomorphic flowers. The underground stem is called tubers and it is the most important part of the plant.  The genus Dioscorea exhibits a number of morphological, anatomical and embryological characters which are reminiscent of dicotyledons (Bouman, 1995).Economically the genus Dioscorea occupies the third most important food crop in the world next to cereals and pulses. The global production is estimated at about 3600 million tonnes (FAO, 2000). Yam is a major staple food in various parts of the world especially in many tropics and subtropical regions (Cooke et al., 1988). Most of the tubers are edible and are also medicinal.   The tubers of some species contain tannins (Ayensu, 1972; 1981). The poisonous principle found in the tuber is mainly of saponins (Burkill, 1935; Coursey, 1967b). Yams are also cultivated for traditional animal feed.Apart from being used as food and certain species of yams like Dioscorea deltoidea and Dioscorea floribunda are important sources of pharmaceutically active compounds. Yam crops have potential for increased commercial exploitation in the area of food processing and pharmaceutical industries (O'Hair, 1988). Nutritionally the yams, like other root or tuber crops are essentially rich in starch or carbohydrate, which provide extra calorie and thus occupies a place comparable to that of potatoes. Yams are also valuable as a source of certain vitamins and contain limited but not insignificant amounts of protein. Therefore in many regions of the world yams are considered as a major food crop and thus they play an important role not only in the nutrition but also an integrated one in the cultural life of the people.In India, there are 32 species of Dioscorea reported of which 21 are distributed in Western Ghats and about 5 million people are directly or indirectly depend on this crop for their food, feed, medicine etc. In spite of its manifold economic importance, the group is not taxonomically well studied for the last 60 years except a few attempts by flora workers. This is mainly because of its dioecious nature, variable phyllotaxy, different phenology of the same species, deep seated underground tubers etc., which makes the group much more difficult for researcher and hence neglected. Against this backdrop, the present study has been undertaken to delimit and unravel the species complexity that exists in the Western Ghats based on fresh explorations from the wild as well as in cultivation for conservation and sustainable utilization.