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DIOSCOREACEAE

(Yam family)

 

The 750 species in 5 genera are found in tropical and warm temperate regions. Typically, they are twining vines arising from underground tubers or rhizomes.

The largest genus, Dioscorea L., is found in tropical and sub-tropical regions. It includes many species of economic importance. Several species, including D. alata L., D. cayennensis Link, and D. trifida L. f. produce edible tubers rich in starch, known as yams. Other species, including D. floribunda Mart. & Gal., D. mexicana Scheidw., and D. villosa L. yield diosgenin, a steroidal sapogenin used in the commercial production of medicinally used steroids.

There have been several reports describing skin irritation following contact with the raw tubers of Dioscorea and Tamus L. species. This may be attributable to the presence of steroidal saponins which can be removed by washing or boiling. The irritancy of Tamus communis berries and rhizomes is certainly attributable, in part, to the presence of calcium oxalate raphides. Several species of Dioscorea bear thorns.


Dioscorea alata L.
White Yam, Water Yam

The raw tuber is irritant to the mucous membrane of the mouth (Burkill 1935). Application of the juice from the root to the skin produces pruritus and desquammation (Piffard 1881).



Dioscorea dumetorum Pax
(syn. Dioscorea triphylla Schimper var dumetorum)

Application of the tuber to the skin produces a burning sensation (Watt & Breyer-Brandwijk 1962).



Dioscorea hispida Dennst.
(syn. Dioscorea cylindrica Burman)
Wild Yam

Quisumbing (1951) reported that ingestion of raw tubers was a frequent cause of death in the Philippines. However, the tubers are edible after grating, repeated washing and soaking, and boiling (Burkill 1935). The toxicity has been attributed to an alkaloid known as dioscorine (Webb 1948a).



Dioscorea transversa R. Br.
Wild Hop Vine

Maiden (1914) described an acute irritation of the hands and arms in persons washing the pulped tubers from this species. The incident occurred in New South Wales during the production of arrowroot, a starch product.



Tamus communis L.
Black Bryony, Blackeye Root, Herbe à la Femme Battue

The fresh rhizome, when scraped or squeezed, yields a colourless mucilaginous sap which has been used as a rubefacient and counter-irritant application in lumbago, rheumatism, and similar disorders (Maheu & Chartier 1927, Perrot & Paris 1971, Wren 1975). The popular names blackeye root and herbe à la femme battue refer to the use of the rhizome as an application to bruises to remove the discolouration (Maheu & Chartier 1927, North 1967).

Both the rubefacient slime from the rhizome and the juice from the berry contain calcium oxalate raphides - measuring an average 450 μm in length and 11 μm in diameter in the berry juice, and an average 250 μm in length and 8 μm in diameter in the slime from the rhizome — which are sharply pointed at both ends. They are responsible for mechanical irritation when rubbed into the skin. In addition, the rhizome contains histamine and saponins, both of which may contribute to the observed skin response following subcutaneous injection by the calcium oxalate raphides (Schmidt & Moult 1983). The irritant effects on the skin may be inhibited by an antihistamine (Holzach & Flück 1951).

Cases of an allergic contact dermatitis from black bryony have been described by Milyavsky (1979) and Fernandez de Corres (1983).

The rhizome and particularly the attractive scarlet berries can cause poisoning when ingested. The symptoms are those of an irritant purgative with burning of the mouth and blistering of the skin (North 1967, Lewis & Elvin-Lewis 1977).

The plant has been confused with the white bryony - Bryonia cretica L. ssp dioica Tutin (syn. Bryonia dioica Jacq.) in the family Cucurbitaceae, from which it may be distinguished readily by its lack of tendrils.


References

  • Maiden JH (1914) Dioscorea transversa R. Br., a yam, native of New South Wales and Queensland. Agricultural Gazette of New South Wales 25(7): 612
  • Watt JM, Breyer-Brandwijk MG (1962) The Medicinal and Poisonous Plants of Southern and Eastern Africa. Being an account of their medicinal and other uses, chemical composition, pharmacological effects and toxicology in man and animal, 2nd edn. Edinburgh: E & S Livingstone [WorldCat] [url]
  • Wren RC (1975) Potter's New Cyclopaedia of Botanical Drugs and Preparations. (Re-edited and enlarged by Wren RW). Bradford, Devon: Health Science Press [WorldCat] [url] [url-2]
  • [Others yet to be added]



Richard J. Schmidt [Valid HTML 4.01!]



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