Dioscorea alata L.
  • Sp. Pl.: 1033 (1753) 


Notes: Distribution: Trop. & Subtrop. Asia

General Description

Tuber replaced annually, normally cylindric, up to 6 cm. in diameter, descending vertically, but in some cultivars very diversely shaped, branched or expanded above, sometimes with lobes curved or spreading horizontally. Twining stems 4-winged or -angled, up to 10 m. long, glabrous. Leaves opposite or the lower alternate, glabrous; petiole up to 9(–10) cm. long; blade ovate with widely cordate almost hastate base, apically narrowed to an acute acumen, up to 12(–13) cm. long and 8(–10) cm. broad. Aerial tubers subglobose or irregularly and narrowly ovoid, up to 12 cm. long. Inflorescences glabrous. Male ± 2 in the leaf-axils or forming axillary terminal panicles in the axils of bracts, spreading; axis zigzag, with the sessile flowers directed forwards and outwards; perianth subglobose, not opening widely, ±1.5 mm. across. Female 1 per leaf-axil, up to 21(–35) cm. long; perianth triangular-subglobose, ± 5 mm. across. Ovary glabrous. Capsule as in fig. 1/4, p. 4, up to 3.5 cm. in diameter, glabrous. Seeds winged all round.

Notes: VARIATION. Whilst the above-ground parts of this yam show comparatively little variation, the tuber, largely as a result of long cultivation and selection by man, has developed a number of very different shapes. NOTE. D. alata has been introduced into Africa from the East, and no doubt a number of different cultivars have become established here and there as crop plants. As it is propagated vegetatively, it is usual to find plants of one sex only in any one locality. Mrs. Faulkner searched for but failed to find a male plant in Zanzibar, where it has become established in natural vegetation. The only plants collected by Peal in Uganda were either female or sterile. I have not yet seen a male flowering specimen from East Africa. As plants of the two sexes seldom grow together, the production of fruit is very rare in Africa. However, D. alata has become well established in secondary vegetation, where it has the appearance of a native plant.

Glabrous climber with winged stems 10-25 ft. high, rarely flowering in our area and usually reproducing vegetatively; bulbils developed in some forms; tubers annual, their shape, size and colour very variable according to the cultivars.

Notes: Numerous varieties producing many different types of tubers, digitate or not, straight, curved or coiled having white, pink or purple flesh. They play an important role in the agricultural economy of W. Africa. Much cultivated throughout the tropics. (See Appendix, p. 489.)

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.

Vertical tubers, with fibers sometimes, in different forms and often ramified, parenchym in different color. Stem in right direction, square in cross section (4 wings), rounded and membranous lateral nodal organ, 6-10 cataphyls (2.5-4mm), bulbils present. Leaves papery, alternate or opposite, base deeply lobed, apex acuminate, 7-9 veins, petiole in variable size, terete, swelling at the base. Compound inflorescence male, spike inflorescence female. Capsule oblong, ascending, short wings around seeds. Species widespread from East to West.

Diagnostic Description

Climber to 25 m. Tubers 1 to several, approximately 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,  grey-brown  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,  18–23  by  25.5–43.5 mm.  Seeds 5–7.5 by 5–6.3 mm, wings 18–21.5 x 15–21.5 mm, all around seed margin

Habitat

HAB. Cultivated for its edible tuber, and often persisting in secondary forest and bushland; the cited specimens from Uganda are all cultivated, as are those from Amani, but D. alata is likely to persist in these areas, as it is doing in Zanzibar; 0–1350 m.

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.

Distribution

tropical eastern Asia, now spread around the humid tropics of both Old and New World

DISTR. U3, 4; T1, 3, 8; Z

  • Tanzania
    • Lushoto District:: Amani, July 1939 (? & ? fl.), Greenway 5884 ! & 5885 !
    • Zanzibar I.,: Kizimkazi, 27 May 1960 (? fl.), Faulkner 2573 ! & Makunduchi, 23 June 1961 (? fl.), Faulkner 2859 !
  • Uganda
    • Masaka District:: 16 km. from Masaka on road to Kampala, 20 Sept. 1958 (sterile), Peal 34 !
    • Mbale District:: N. Bugisu, Bumasifwa, 26 Sept. 1958 (sterile), Peal 23 !
    • Mubende District:: about 15 km. from Kakumiro, 30 Sept. 1957 (sterile), Peal 14 !

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.

Conservation

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.

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.

Edible tubers after cooking

Type Material

Types: Ceylon, {i}Hermann{/i} 2: 23 (BM, syn.) & without data, {i}Linnean Herbarium{/i} 1184.2 (LINN, syn., IDC microfiche !)

Literature

Sp. Pl.: 1033 (1753); Bak. in F.T.A. 7: 417 (1898); R. Knuth in E.P. IV. 43: 265 (1924); F.W.T.A. 2: 382 (1936); Burkill in B.J.B.B. 15: 380 (1939) & in FL Males., ser. 1, 4: 330 (1951); Miège in F.W.T.A., ed. 2, 3: 152 (1968); Verdc. & Trump, Common Poisonous Pl. E. Afr.: 192 (1969).

Sp. Pl. 1033 (1753); F.T.A. 7: 417; Knuth l.c. 265; Prain & Burkill l.c. 308; Burkill l.c. 380; Miège in Rev. Bot. Appliq. 32: 144 (1952); Miège, Contrib. Dioscor. 94 (1952).

Distribution Map

 
  • Native distribution
  • Introduced distribution
Specimens
Found in
  • Asia-Temperate Eastern Asia Nansei-shoto
  • Taiwan
  • Asia-Tropical Indian Subcontinent Assam
  • East Himalaya
  • Nepal
  • Indo-China Cambodia
  • Myanmar
  • Thailand
  • Vietnam
  • Malesia Borneo
  • Christmas I.
  • Jawa
  • Lesser Sunda Is.
  • Malaya
  • Philippines
  • Sulawesi
  • Sumatera
  • Papuasia Bismarck Archipelago
  • New Guinea
Introduced into
  • Africa East Tropical Africa Tanzania
  • Northeast Tropical Africa Ethiopia
  • South Tropical Africa Angola
  • Malawi
  • Mozambique
  • Zambia
  • West Tropical Africa Benin
  • Burkina
  • Guinea-Bissau
  • Mali
  • Senegal
  • Togo
  • West-Central Tropical Africa Burundi
  • Cameroon
  • Central African Republic
  • Gabon
  • Gulf of Guinea Is.
  • Rwanda
  • Zaire
  • Western Indian Ocean Comoros
  • Madagascar
  • Seychelles
  • Asia-Temperate China China South-Central
  • China Southeast
  • Eastern Asia Kazan-retto
  • Asia-Tropical Indian Subcontinent Maldives
  • Indo-China Andaman Is.
  • Australasia Australia Northern Territory
  • Queensland
  • Northern America Mexico Mexico Southeast
  • Southeastern U.S.A. Florida
  • Georgia
  • Pacific Northwestern Pacific Caroline Is.
  • Marianas
  • South-Central Pacific Pitcairn Is.
  • Society Is.
  • Southwestern Pacific Fiji
  • Niue
  • Samoa
  • Santa Cruz Is.
  • Tonga
  • Wallis-Futuna Is.
  • Southern America Brazil Brazil West-Central
  • Caribbean Bahamas
  • Cuba
  • Dominican Republic
  • Haiti
  • Jamaica
  • Leeward Is.
  • Puerto Rico
  • Southwest Caribbean
  • Trinidad-Tobago
  • Venezuelan Antilles
  • Windward Is.
  • Central America Belize
  • Costa Rica
  • El Salvador
  • Guatemala
  • Honduras
  • Nicaragua
  • Panamá
  • Northern South America French Guiana
  • Guyana
  • Suriname
  • Venezuela
  • Western South America Colombia
  • Peru

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Flora of West Tropical Aftrica (FWTA)
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