Dioscorea

Family: Dioscoreaceae, 8 genera.
Genus: Dioscorea, +-600 species.
Derivation: Dioscorea, in honour of Pedanios Dioscorides, the first-century Greek physician and herbalist who compiled Materia Medica dealing with medicinal herbs.
General description: Climbers with tuberous or thick woody rootstock. Stems mainly annual. Tubers may be clustered or solitary, underground, above ground or even aerial (as in D.bulbifera). Male and female flowers on seperate plants. Widespread in the tropics and sub-tropics.

SPECIES

Probably the best known and the most widespread in cultivation is

- D.elephantipes (L'Her.) Engl. (elephantipes = like an elephant's foot) from the southern Cape, South Africa
Large, above-ground caudex, splitting into squares with age, giving it a look much like a tortoise's back. Annual stems with heart-shaped leaves.

- D.macrostachya Benth. from Mexico has a caudex nearly identical to D.elephantipes, almost indistiguishable when not in leaf. First described in 1841 but only brought into cultivation in 1964 and first sold by the ISI in 1968. Leaves much larger, ovate, tapering to a long point and with more veins than elephantipes. Flowers tassel-like inflorescences made up of tight bunches of two to three blooms. It is said to be more tender than D.elephantipes.

- D.sylvatica (Kunth) Eckl. is subdivided into 5 varieties, namely:
var.brevipes (Burtt Davy) Burkill,
var.multiflora (Marloth) Burkill,
var.paniculata (Dummer) Burkill,
var.rehmannii (Baker) Burkill,
var sylvatica
(sylvatica = growing in woods and forests)
Very widespread from the Eastern Cape to Central Africa. Slender climber up to 15 m, heart-shaped leaves. Large flattenend tuber with reticulate markings, exposed above ground or buried.

- D.hemicrypta Burkill from the Western Cape (Vanrhynsdorp) has a half-buried caudex, warty where exposed and smooth, erratically lobed segments underground.

Other species seen in cultivation, with underground, clustered tubers are:

- D.cotinifolia Kunth, eastern parts of South Africa. Leaves heart-shaped.
- D.dregeana (Kunth) T.Durand & Schinz, (named after Johann Drege, 1794 - 1881, a German botanist who collected in the Cape in 1826) E.Cape to N.Prov, South Africa. Trifoliate, large, slightly hairy leaves.
- D.rupicola Kunth, (rupicola = growing in stoney places) E.Cape to N.Prov, South Africa. Leaves heart-shaped with 5 - 7 lobes.

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References:
- Gordon D.Rowley 'Caudiciform & Pachycaul Succulents',
Strawberry Press, 1987
- Gerrit Germishuizen 'Wild Flowers of Northern South Africa',
Fernwood Press, 1997
- National Botanical Institute of South Africa & SSSA
'List of Southern African Succulent Plants' Umdaus Press, 1997
- Elsa Pooley 'A field Guide to the Wildflowers of KwaZulu-Natal and
the Eastern Region', Natal Flora Publications Trust, 1998

DIOSCOREA - TRADITIONAL MEDICINAL USES

Quickly, before my 2 weeks on Dioscorea run out, a few words on the medicinal use of Dioscorea. I am limiting my quotes to the South African species, as obviously this is closer to home for me. If you would like to read up on the various uses of other species, have a look at the Ethnobotany site at http://www.rain-tree.com/dioscorea.htm . This site also contains lots of links to other resources and pictures.

'None of the South African species are used commercially, but there are several Central American, Indian and Chinese species of importance in the extraction of steroidal saponins which are hydrolysed to diosgenin. The compound is used as a starting material in steroid hormone semi-synthesis, to produce cortisone and contraceptives.'

D.elephantipes, D.dumetorum, D.rupicola
One of the common names of D.elephantipes is 'Hottentot's Bread'. It is said to be edible after leaching and is reported to have been an important food item for the early Cape people, but practically no information on it's traditional food use seems to have survived. Others such as D.dumetorum and D.rupicola are said to be emergency foods.

D.sylvatica
"Root decoctions are taken for chest conditions, including bronchiectasis, and as 'blood-purifiers' and ritual emetics. Infusions of the tuber, and crushed tuber, are applied topically to swellings and rashes. The tubers contain diosgenin, which can be readily extracted and purified and can be converted into a medicinal steroid. Diosgenin from the tubers was used to produce oral contraceptive compounds in the 1950's."

D.dregeana
"is frequently sold on the 'muthi' markets in South Africa. The common Zulu names 'uDakwa' and 'isiDakwa' respectively mean 'inducing drowsiness' and 'a drunkard'. It is a profound sedative that is commonly used to treat epilepsy, hysteria, insomnia, and acute psychosis. this potent narcotic is used to sedate violent, psychotic patients and is also used as an analgesic. In earlier times it was used as a general anaesthetic to enable fractures of the limbs to be manipulated and stabilised by traditional bone-setters." "Hallucinations have not been reported from the use of the tuber on its own, but do occur when combined with the known hallucinogen Boophane disticha for the purposes of divination. Dried and powdered , the tuber is used in small amounts as a remedy for colic and restlessness in infants. The tuber may be hollowed out, and water heated in it is used as a lotion for cuts and sores in humans and animals. The cut surface of the tuber can be rubbed directly against the skin to treat scabies rashes." "The plant has apparently been used with criminal intent on trains, by administering it in food or drink so that the victim can be robbed while senseless. Some indigenous healers maintain that the use of this plant is behind tales of zombies, and resurrection of the dead. Since the plant is potentially highly toxic and can cause fatalities, it is only used by indigenous healers skilled in its use. Maize cobs boiled in strong decoctions of the tuber are fed to monkeys to destroy them. Tubers have been eaten as famine food after soaking them in running water for several days a process that leaches out toxic principles. Alkaloids are most likely responsible for the sedative activity."

As you can see, the various Dioscorea species vary from 'important food crops' to 'potentially toxic' plants. I do not suggest you go and try it out in any way, unless you have several years of 'sangoma' training!
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References:
- Ben-Erik van Wyk & Nigel Gericke 'People's Plants',
Briza Publications, 2000
- Ben-Erik van Wyk, Bosch van Oudtshoorn, Nigel Gericke,
'Medicinal Plants of South Africa', Briza Publications, 1997
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Maddy