Dioscorea cirrhosa (PROSEA)
Introduction |
Dioscorea cirrhosa Lour.
- Protologue: Fl. Cochinch. 2: 625 (1790).
- Family: Dioscoreaceae
- Chromosome number: 2n= unknown
Synonyms
- Dioscorea rhipogonoides Oliv. (1889),
- Dioscorea matsudai Hayata (1921).
Vernacular names
- Dye-yam, dyeing yam, dye-root (En)
- Faux gambier (Fr)
- Laos: thoom lüad, kabau, houa
- Vietnam: cu'nâu (general), khoai leng (central).
Origin and geographic distribution
Dye-yam is a native of north-eastern Thailand, Laos, Vietnam, south-eastern China (Provinces Guangxi and Guangdong), Hong Kong, Taiwan, and the southern Ryukyu Islands. Throughout this area it is sometimes also cultivated.
Uses
The tubers are widely used as a source of a reddish-brown dye for colouring cloth, and as a source of a tanning material for toughening fishing nets or to prepare leather from hides.
In southern China cotton cloth and grass cloth made of ramie ( Boehmeria nivea (L.) Gaudich.), as well as silk, are dyed with a solution of the tubers. In Indo-China cottons are dyed with dye-yam.
Production and international trade
At the beginning of the 20th Century, dye-yam was an important product for export from northern Vietnam, with a maximum shipping to Hong Kong of 8000 t/year. Since 1930 exports have rapidly diminished. The main reason for this decline is undoubtedly the increasing use of synthetic dyes, but excessive exploitation of the wild populations of this species may also have caused the market to decline, as happened at the end of the 19th Century in Hong Kong. At present, dye-yam is only of local importance.
Properties
Tubers contain 6.5-14% tannin. Dye-yam imparts a dark red colour to leather, and a brown colour to fishing nets. Dimeric, trimeric and tetrameric procyanidins have been isolated from the tubers, together with (+)catechin and (-)epicatechin.
The dye is extracted from the reddish flesh of tubers. It is soluble in hot water, less soluble in cold water, and almost insoluble in alcohol. A viscous extract has been prepared in Vietnam, yielding 4% of the tuber weight. This extract contained about 35% of tanning and dyeing material, soluble in hot water.
Botany
A perennial dioecious herb up to 10 m long, glabrous and scandent, with tuberous rhizome (of 1 or more tubers) of variable shape and size, usually globose or pear-shaped and up to 10 cm in diameter; stems twining to the right, terete and slender, glabrous but near base often with curved prickles, yellow to brown.
- Upper leaves opposite, papery to thinly leathery, elliptic-ovate or elliptic-lanceolate, 8-14 cm × 2-5 cm, rounded to obtuse at base, acute or acuminate at apex, 3-5-nerved; lower leaves often alternate and larger, subcordate at base, up to 9-nerved; petioles 1.5-4 cm long, slender.
- Male flowers in axillary panicles composed of spikes, or in simple spikes up to 8 cm long, 6-merous, small.
- Female flowers in axillary pendant spikes up to 10 cm long, each flower with an inferior 3-loculed ovary and 3 bifid stigmas.
- Fruit a 3-valved winged capsule, 1.5-2.5 cm × 2.5-4 cm, shortly stipitate, retuse at apex.
- Seeds winged.
In the literature, dye-yam is sometimes erroneously reported for the Philippines. This mistake probably arose because Knuth (1924) mistakenly cited D. cirrhosa specimens for the Philippines instead of D. merrillii Prain & Burkill.
Ecology
Dye-yam occurs naturally in thickets and secondary forests, usually in the lowland, in southern China up to 1500 m altitude. It is sometimes not clear whether plants are truly wild or have escaped from cultivation and naturalized, as is often the case with other Dioscorea species.
Propagation and planting
Plants can easily be propagated by tubers, which are planted near trees in the forest or in waste land, using sticks as staking material. Tubers are usually collected from plants in the wild.
Handling after harvest
When about 3 years old, the tubers are harvested in the dry season when the red flesh has a high tannin content. The tubers should be harvested with care to ensure that they are not broken or bruised. They should be protected against desiccation because they lose much of their colouring properties when desiccated. For dyeing and tanning purposes, the tubers are peeled and the flesh is rasped. About 3 l of water is added to 1 kg of rasped flesh, and clothes or nets are dipped in the hot or cold solution remaining after filtering, and afterwards dried in the sun. This handling is repeated several times, until the desired reddish-brown colour is attained. The dye rapidly loses its activity, and best results are obtained with fresh solutions. Mordants such as alum, aluminium acetate and bichromate are often added to the solution, but sometimes leaves of Psidium guajava L. and Piper betle L., or mud (in China) replace the mordant. Occasionally, clothes are dyed first with other vegetable dyes, such as the bark of Bruguiera gymnorhiza (L.) Savigny.
Prospects
In the future, when the use of natural dyes might increase again, dye-yam could be a potential substitute for synthetic dyes. The dyeing and tanning solutions are fairly easy to prepare and use. Besides, dye-yam is a herbaceous plant which is much faster and easier to grow than numerous arborescent dye and tannin-producing species. More research is desirable on its dyeing and tanning properties, on the prospects for this species in South-East Asia, and on methods of cultivation.
Literature
- Coursey, D.G., 1967. Yams. Longmans, London. pp. 49, 150, 167, 208.
- Crevost, Ch. & Pételot, A., 1941. Catalogue des produits de l'Indochine. Tome 6. Tannins et tinctoriaux. Gouvernement général de l'Indochine, Hanoi. pp. 87-91.
- McClure, F.A., 1927. Note on a Chinese vegetable dye. The Lingnaam Agricultural Review 4: 31-37.
- Walker, E.H., 1976. Flora of Okinawa and the southern Ryukyu Islands. Smithsonian Institution Press, Washington, D.C., USA. p. 320.
Authors
Nguyen Tien Hiep & R.H.M.J. Lemmens