Dioscorea dregeana

(Kunth) T.Durand & Schinz

Family : Dioscoreaceae
Common names : Wild yam (Eng.); wildejam (Afr.); ingcolo (Xhoza); isidakwa (Zulu)

Trifoliate leaves: Photo Geoff Nichols

©Geoff Nichols

The twining, pale green and tuberous Dioscorea dregeana can be used in different ways for different purposes. It is a useful medicinal plant of the Zulus; however it is poisonous to humans and animals.

Description
Dioscorea dregeana is a perennial, herbaceous creeper, twining, up to 15 m long. It has a slightly thorny stem growing annually from a fleshy, tuberous rootstock.

Thorny stem
©Geoff Nichols

The stems are produced in spring and tend to die off in winter. The underground fleshy tuber grows up to 300 mm in diameter.

Rootstock and stem Ngoye forest .Geoff Nichols
©Geoff Nichols

The leaves are large, alternate, 3-foliolate, covered with silvery, velvet hairs, broadly ovate, with apex attenuate, up to 150 x 110 mm. The flowers are white, inconspicuous and borne in slender, branched clusters that hang down from the stems. The male and female flowers are borne on separate plants. The fruits are pale green, winged and up to 50 x 25 mm. The flowering time: October–January.

Conservation status
According to Raimondo et al. (2009), Dioscorea dregeana was of Least Concern (LC), when it was evaluated against the five IUCN criteria, as it does not qualify for the categories Critically Endangered, Endangered, Vulnerable or Near Threatened.

Distribution and habitat
Dioscorea dregeana occurs naturally in woodlands, forests and bush clumps in the eastern parts of southern Africa. It is found in Limpopo Province, Mpumalanga, Swaziland, KwaZulu-Natal and Eastern Cape.

Derivation of name and historical aspects
The genus Dioscorea was named after Pedanios Dioscorides, a Greek physician in the first century AD. The specific name ‘ dregeana ' is in honour of the German collector Johan Franz Drège.

Ecology
Little is known about the ecology of this species.

Uses and cultural aspects
Dioscorea dregeana is commonly sold on the ‘ muthi ' markets in South Africa. It may be used in different ways for different purposes. The Zulus use it as a sedative in the treatment of epilepsy, hysteria, insomnia and acute psychosis. The Zulu name ‘ isidikwa ' means ‘drunkard', referring to the reported effects that it may have. It is also used topically for scabies. In ancient times, it was used as a general anaesthetic to enable fractures of the limb to be manipulated and stabilised by traditional bone-setters. The fresh tuber is generally taken orally as a weak decoction, with an adequate dose resulting in sleep within 20–30 minutes. Dioscorea dregeana is sometimes combined with Boophone disticha for the purpose of divination.

However, human deaths have been reported after the use of the plant as famine food or as medicine. This species is reported to make a person ‘mad drunk' and it has been used in poison bait to destroy monkeys. This Dioscorea, due to its toxicity,is often planted to eradicate moles (intukuzi ) in the fields and home gardens. It is often planted together with crops, especially root and tuber plants, such as amabhatata ( Ipomoea batatas, sweet potato) and amadumbe Colocasia esculenta, coco yam).

Leaves and twining stems.G.Nichols

©Geoff Nichols

Growing Dioscorea dregeana

Dioscorea dregeana can be grown from seeds. The seeds are sown in spring, and germination occurs after 10 days in seedling mix. The seedlings grow best in warm temperatures and must be watered once a week. The plant goes dormant during winter and should not be disturbed.

References and further reading

  • Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds). 2009. Red List of South African plants 2009. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
  • Retief, E., Herman, P.P.J. 1997. Plants of the northern provinces of South Africa: Keys and diagnostic characters. Strelitzia 6. National Botanical Institute, Pretoria.
  • Van Wyk, B.-E., & Gericke, N. 2000. People's plants: A guide to useful plants of southern Africa . Briza Publications, Pretoria.
  • Van Wyk, B.-E., Van Heerden, F. & Van Oudtshoorn, B. 2002. Poisonous plants of South Africa. Briza Publications, Pretoria.
  • Van Wyk, B.-E. Van Oudtshoorn, B. & Gericke, N. 2009. Medicinal plants of South Africa , edn 2. Briza Publications, Pretoria.
  • Zukulu, S., Dold, T., Abbott, T. & Raimondo, D. 2012. Medicinal and charm plants of Pondoland . South African National Biodiversity Institute, Pretoria.

 

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