Dioscorea alata

General description: 

Climber to 25 m. Tubers 1 to several, c. 10–50 by 5–30 cm, very variable in shape, in “wild” races usually cylindric to clavate, in cultivated races often globose to subglobose or clavate to digitate, known to be lobed or branched in parts of its range (Prain & Burkill 1938), with any underground part being able to give rise to a new plant. Indumentum absent. Stems 5–15 mm in diam. at base, woody and spiny, right-twining, usually quadrangular in cross section with a longitudinal wing on each angle (also petioles and often inflorescence axes). Leaves simple, opposite, blade ovate to broadly so on the lower stems, base often sagittate to auriculate, ovate with a cordate, rounded or truncate base on distal stems, chartaceous, (5–)7–9-veined, margins entire, apex acuminate; lateral nodal flanges present as a membranous semi-circular or auriculate wing at each node; cataphylls 6–10 by 2.5–4 mm, lanceolate to narrowly ovate; bulbils present in many cultivated races, 2–7 cm in diam., globose or subglobose to clavate, greybrown to dark brown with a smooth or finely warty epidermis. Inflorescences pendent, spicate; male simple ((1 –)2–6 (–10) per axil) or compound (1–2 per axil); partial/simple inflorescence axes flexuous; female inflorescences simple, 1(–2) per axil, elongating in fruit. Male flowers with outer tepals 1.3–1.6 by 1.0–1.3 mm, broadly obovate, inner tepals 0.9–1.1 by 0.8–0.9 mm, obovate to shortly spatulate; stamens 6, erect. Capsules 18–23 by 25.5–43.5 mm. Seeds 5–7.5 by 5–6.3 mm, wings 18–21.5 by 15– 21.5 mm, all around seed margin.

General Description Reference: 
Wilkin, P. & Thapyai, C. Dioscoreaceae. Flora of Thailand 10, 1–140 (2009).
Conservation status: 

IUCN red list category LC (IUCN 2001). D. alata is widespread and common, growing in most habitats except swampy areas. Nevertheless, there may well be endangered races or varieties in Thailand. This needs further investigation; ancient races may provide resistance genes to, for example, anthracnose for plant breeders.

Distribution: 

Thailand, A cultigen, probably of South-East Asian origin, now pantropically cultivated for its tuber. Type: two syntypes, one from from Sri Lanka and one of unknown origin.

Habitat: 

Found in open degraded and disturbed areas, mixed deciduous forests, pine and hill evergreen forests and in cultivation from near sea level to 1,250 m. Apparently “wild” plants are probably relicts of cultivation. These populations appear to reproduce sexually to a considerable extent in Thailand.

Uses: 

In Thailand, cultivation of D. alata is often relatively small-scale, for example in gardens with fruit crops. Both cultivated and apparently wild plants provide edible tubers which are available in local or roadside markets. In cultivated races, the tubers are never over 50 cm deep and shallowly horizontally buried, while in “wild” plants they descend vertically into the substrate to c. 150 cm. Propagation is usually by tubers or bulbils planted in rainy season. Some cultivated races do not produce flowers. The tubers are usually dug in the dry season the year after planting, when the above-ground parts have died back. They are peeled, sliced into small pieces and washed or soaked in water, then boiled or steamed as an alternative starch source to rice. Steamed or boiled D. alata tubers can be served with coconut and sugar or cooked as a dessert with sugar and coconut milk.

Taxonomic Notes: 

This species is easily recognised by the four longitudinal wings on its stems and petioles.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith