Prota 3: Dyes and tannins/Colorants et tanins
U.S. Dept. Agric. Bur. Pl. Ind. Bull. 176: 29 (1910).
Mimosaceae (Leguminosae - Mimosoideae)
Acacia elephantina Burch. (1824), Elephantorrhiza burchellii Benth. (1841).
Elephant root, elandsbean (En).
Origin and geographic distribution
Elephantorrhiza elephantina is found in southern Africa in Namibia, Botswana, Zimbabwe, Mozambique, Swaziland, Lesotho and South Africa.
The bark of the tuberous rhizome (usually including the roots) of Elephantorrhiza elephantina is a popular source of tanning and dyeing materials, collected from the wild and sold on local markets in southern Africa. Rhizomes or their bark only are crushed, some water is added and the resulting paste is applied to hides to tan and dye them a reddish colour described as a pale wine colour in Botswana. This treatment also serves to soften the leather. To dye grass for mat and basket weaving, the pounded rhizomes are boiled with the grass for several hours, giving a khaki, brown or reddish brown colour. The young shoots are eaten by livestock. The seed has a sweetish taste followed by a burning sensation, but roasted it has been used as a coffee substitute. Medicinally, the rhizome is used as a general remedy for intestinal and abdominal complaints (diarrhoea, dysentery, stomachache, painful menstruation) for humans and animals, as a relief for heart troubles and haemorrhoids, and to cure skin diseases and acne. The root is steeped in water for 24 hours or longer, after which it is strained and ready for external use. For internal use, the infusion has to be boiled for 10 minutes first. The face is held in the vapour arising from a warm infusion to treat acne. In Zimbabwe an infusion is taken by women against infertility and as an aphrodisiac.
The rhizome of Elephantorrhiza elephantina contains 622% tannin and 17% sugar. The bark contains 2530% tannin. The rhizome extract contains too much sugar for commercial exploitation as it tends to ferment. The leather gets dyed in reddish tones that may be undesirable when light-coloured leather is needed. Dye experiments on wool with a rhizome extract gave different colours according to the mordants used, e.g. yellow with stannous chloride, golden to orange with chromium chloride, orange-brown with ammonium molybdate, black with ammonium vanadate, and salmon with sodium wolfram or zinc sulfate. The seed yields 10% of a fixed oil. The seed is toxic to sheep (lethal dose 250 g), rabbits (lethal dose 57.5 g/kg) and guinea-pigs, causing gastro-enteritis and pulmonary oedema.
Low shrub, producing at ground level annual stems 2090 cm tall from the woody end of an elongate, often thickened rhizome up to 8 m long. Leaves alternate, bipinnately compound, almost glabrous; petiole up to 8 cm long, rachis up to 18 cm; pinnae 24 pairs in lower leaves, 717 in upper ones, axis up to 10 cm long; leaflets up to 55 pairs per pinna, linear to oblong, 415 mm Χ 0.52.5 mm, base asymmetric, apex acute and usually mucronate. Inflorescence an axillary raceme, usually confined to the lower part of the stem, solitary or clustered, including peduncle up to 12 cm long. Flowers bisexual, regular, 5-merous; pedicel up to 1.5 mm long, at base with red-brown glands, articulated near the middle; calyx campanulate, almost 2 mm long, toothed; petals free or slightly connate basally, linear-oblong, 24 mm Χ 1 mm, yellow-white; stamens 10, free, filaments up to 6.5 mm long; ovary superior, shortly stipitate, style filiform, stigma terminal. Fruit a compressed-oblong, straight or slightly curved pod 521 cm Χ 36 cm, red-brown, prominently transversely veined, often swollen over the seeds, the valves separating from the persistent margins, the outer layer of the fruit wall peeling off the inner layer and the layers breaking up irregularly. Seeds compressed-ellipsoid, 1826 mm Χ 1318 mm Χ 613 mm.
Elephantorrhiza comprises 9 species, all restricted to Africa south of the equator. Elephantorrhiza elephantina is quite variable in the number of pinnae and number, size and shape of leaflets. In the eastern part of its distribution area plants tend to have most pinnae with smallest leaflets. The outer layer of the ripe fruit is rather hard but readily absorbs water and starts to disintegrate soon. Seeds often germinate within the moist disintegrating fruits on the surface of the soil.
In Botswana the rhizome of the related but larger Elephantorrhiza burkei Benth. is also used for tanning and dyeing, giving a khaki colour, while the bark is used as an astringent. The crushed rhizomes of Elephantorrhiza suffruticosa Schinz, found from Namibia to Mozambique, were used as red dye for the tanned cow stomachs formerly worn as aprons or skirts by the Kwanyama Ovambo women of northern Namibia. In Zimbabwe the rhizome is applied against constipation and diarrhoea. From the roots and stem of Elephantorrhiza goetzei (Harms) Harms, a small tree found from Angola to Tanzania and further southwards, compounds (e.g. flavans, stilbene glycosides) with promising antimicrobial and anthelmintic activities have been isolated. In Malawi its fibrous stem bark is used as rope and the tannin-rich roots as a fish poison.
Elephantorrhiza elephantina often occurs gregariously in hot, dry areas with grassland and open scrub.
Genetic resources and breeding
Although Elephantorrhiza elephantina is widespread, overharvesting of rhizomes for tanning or medicinal purposes might endanger populations so that germplasm collection is recommended.
Elephantorrhiza elephantina is only of minor importance locally in rural areas in southern Africa as a tannin, dye and medicine source. More research is required for reliable expectations.
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Correct citation of this article:
Jansen, P.C.M., 2005. Elephantorrhiza elephantina (Burch.) Skeels In: Jansen, P.C.M. & Cardon, D. (Editors). PROTA 3: Dyes and tannins/Colorants et tanins. [CD-Rom]. PROTA, Wageningen, Netherlands.