Root crops have sustained many indigenous communities all over the world. Some of the main plants that are endowed with edible underground parts are Dioscorea (about 600 species worldwide), Amorphophallus (100 species worldwide), Colocasia (10 species worldwide), and include plants from the families Solanaceae (potato family) and the Convolvulaceae (sweet potato family). Underground parts of several orchids too are harvested and eaten, as are the bulbs of some plants of the Lily family; the rhizomes of many wild gingers Hedychium, Alpinia Zingiber, Costus are also edible, some of them with high medicinal value.
However, one of the most important families of tubers is the Dioscoreaceae, many of which have come under cultivation, especially the Dioscorea alata and the Dioscorea bulbifera. At least 25 species are well known in India and eaten by various indigenous communities. Many of the species need specific skills in harvesting and processing, the later very crucial and important as the tubers may contain toxic principles in their composition and require neutralizing. Most of the true yams are known to contain high levels of P and Ca, both important for bones, teeth and skeleton-building; some yams also contain trace elements and minerals not available in most common foods. The family gets its name after Pedanios Dioscorides, the Greek herbalist who lived in the 1st century.
- Almost all the species are climbers and climb by twining on a support
- The climbing is oriented either to the left or to the right and is constant for the species in all conditions
- The leaves of all species – whether compound or simple – have hardened tips
- Some species bear ‘fruit’ known as bulbils which may be edible, as in the case of D.bulbifera; the bulbils may also be used to grow a new plant (as we use seeds)
- The fruit of most species is a capsule and dehiscent, bearing usually winged seeds
Though it is fairly easy to identify the genus/family it is often difficult to identify the exact species with confidence. This is perhaps because of the variability of the vegetative characters of the same plant in different locations and the fact that some species have been under cultivation over thousands of years and have become modified (changes in tuber quality, colour, size and shape, etc.). In addition, the tubers of many wild species are harvested only in the dry season when the ‘above-ground’ parts have dried and wilted, which means that the whole plant has seldom been the attention of proper and prolonged study.
A small nursery to document and understand yams and tubers has been established in Kudhraiyar at the foot of the Palni Hills in Tamil Nadu. Along with the yams there are also several other wild foods in the nursery. Many partners in the network work with communities that harvest and consume root crops though this practice is declining due to various reasons that range from subsidized government food, to loss of traditional knowledge about processing wild tubers, to the influx of modern fast food. One of the tasks of the network is a revival of the consumption of wild tubers among the indigenous communities.
Pictures show the various parts of Dioscorea daemona, a wild yam, found in many parts of central and southern India.