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Obetia tenax (N.E.Br.) Friis

Kew Bull. 38: 226 (1983).
Urera tenax N.E.Br. (1888).
Vernacular names
Tree nettle, mountain nettle, rock tree nettle (En).
Origin and geographic distribution
Obetia radula is distributed in Botswana, Zimbabwe, Mozambique, South Africa and Swaziland.
The bark yields a fibre which is made into tough cords, ropes, nets and mats. The bark is used for thatching. The leaf is cooked as a green vegetable (often mixed with that of Pouzolzia mixta Solms) and eaten with porridge. Root pulp is applied on snakebites.
The bark fibre is strong. The wood is soft and fibrous, with a spongy pith or hollow centre. Contact with the stinging hairs causes intense itching and burning, and may result in blisters on the skin.
Deciduous shrub or small tree up to 5(–7) m tall, presumably dioecious; outer bark purplish brown to grey, often longitudinally striate, large leaf scars present; younger branches densely covered with stinging hairs. Leaves alternate, simple; stipules free, lateral, lanceolate, 4–8 mm × 1–2.5 mm, apex long-acuminate, glabrous; petiole up to 14 cm long, with stinging hairs; blade ovate to almost circular, sometimes slightly 3-lobed, 3.5–15(–17) cm × 3–11.5(–19) cm, base broadly cordate, truncate or rounded, apex rounded, acute or broadly acuminate, margin coarsely toothed, upper surface with stinging hairs and a few stiff hairs, lower surface with scattered stiff hairs and stinging hairs along the veins. Inflorescence an axillary, much branched panicle, up to 10 cm long, with numerous stinging hairs. Flowers unisexual, very small, whitish to yellowish green; male flowers in dense inflorescences, regular, 5-merous, pedicellate, 1–2 mm in diameter, tepals usually with stinging hairs, rudimentary ovary present; female flowers solitary or in small clusters along axes and branches of inflorescence, 4-merous, shortly pedicellate, c. 1 mm long, outer pair of tepals smaller than inner pair, both pairs becoming thinly membranous, glabrous, ovary superior, ovoid, staminodes absent. Fruit an achene c. 1.5 mm long, compressed, ochre to brown, enc1osed by the persistent membranous perianth.
Obetia tenax flowers in August–September and fruits in October–November.
Obetia comprises 8 species, distributed in eastern Central Africa, East Africa, southern Africa and the Indian Ocean islands, mostly in dry habitats.
Obetia tenax occurs from sea level up to 1800 m altitude, in deciduous bushland in rocky locations.
Genetic resources and breeding
It is unknown whether Obetia tenax is threatened by genetic erosion.
Obetia tenax is a useful local source of fibre for cordage. Detailed information on the fibre properties is lacking, however, making it difficult to assess the prospects for this species. The presence of stinging hairs makes handling of the plant difficult.
Major references
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Friis, I., 1991. Urticaceae. In: Launert, E. & Pope, G.V. (Editors). Flora Zambesiaca. Volume 9, part 6. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 79–116.
• Friis, I. & Immelman, K.L., 2001. Urticaceae. In: Germishuizen, G. (Editor). Flora of southern Africa. Volume 9. National Botanical Institute, Pretoria, South Africa. 36 pp.
• van Wyk, B. & van Wyk, P., 1997. Field guide to trees of southern Africa. Struik Publishers, Cape Town, South Africa. 536 pp.
Other references
• Cavendish, W., 1999. The complexity of the commons: environmental resource demands in rural Zimbabwe. The Centre for the Study of African Economies Working Paper Series. Working Paper 92. 52 pp.
• CJB & SANBI, 2006. African Flowering Plants Database. [Internet] Conservatoire et Jardin botaniques de la Ville de Genève (CJB) and South African National Biodiversity Institute (SANBI), Pretoria, South Africa. cjb/bd/africa/ index.php. Accessed March 2009.
• Friis, I., 1983. A synopsis of Obetia (Urticaceae). Kew Bulletin 38(2): 221–228.
• Hyde, M.A. & Wursten, B., 2009. Urticaceae. [Internet ] Flora of Zimbabwe. speciesdata/ family.php?family_id=227. Accessed March 2009.
• Loffler, L. & Loffler, P., 2005. Swaziland tree atlas. Southern African Botanical Diversity Network Report No 38. SABONET, Pretoria, South Africa. 188 pp.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Shackleton, S.E., Dzerefos, C.M., Shackleton, C.M. & Mathabela, F.R., 1998. Use and trading of wild edible herbs in the central lowveld savanna region, South Africa. Economic Botany 52(3): 251–259.
• Watt, J.M. & Breyer-Brandwijk, M.G., 1962. The medicinal and poisonous plants of southern and eastern Africa. 2nd Edition. E. and S. Livingstone, London, United Kingdom. 1457 pp.
M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
E.G. Achigan Dako
PROTA Network Office Africa, World Agroforestry Centre (ICRAF), P.O. Box 30677-00100, Nairobi, Kenya

Correct citation of this article:
Brink, M., 2009. Obetia tenax (N.E.Br.) Friis. In: Brink, M. & Achigan-Dako, E.G. (Editors). Prota 16: Fibres/Plantes à fibres. [CD-Rom]. PROTA, Wageningen, Netherlands.