Prota 16: Fibres/Plantes à fibres
Index Kew. 3: 323 (1895).
Obetia pinnatifida Baker (1883).
Stinging nettle tree (En).
Origin and geographic distribution
Obetia radula is distributed in eastern DR Congo, Rwanda, Burundi, Kenya, Uganda, Tanzania, Comoros, Mayotte and Madagascar.
The stem yields a fibre of good quality used in basketry and for making strong cordage and textiles. It can be made into high-quality paper, e.g. for banknotes. In Madagascar the fibre was formerly used to ignite fire.
In traditional medicine in Kenya a root infusion is given to treat infertility in women. In Uganda the boiled root is chewed against premature ejaculation, and the root and leaf are used in the treatment of cough. In DR Congo the leaf is crushed and the juice instilled in the nostrils for the treatment of madness. In Kenya the leaf juice or a leaf extract is used as mouthwash for treatment of toothache. In Madagascar a decoction of unspecified plant parts is given as an antispasmodic in case of whooping cough and asthma. The leaf is used in East Africa to deter rats and moles. In Kenya and Madagascar the plant is considered to have magic properties.
The fibre is beautiful, and much appreciated in Madagascar. The wood is soft with much sap in it. Contact with the stinging hairs on the leaf causes intense itching. Both fresh and dried stinging hairs have stimulating effects on isolated guinea pig ileum. Compounds isolated from the stinging hairs and possibly contributing to the stinging effect include histamine, serotonin and acetylcholine.
Deciduous shrub or small tree up to 13 m tall, sparsely branched, presumably dioecious; bole up to 50 cm in diameter; outer bark grey or brown, smooth to flaky, with very noticeable leaf scars; branchlets covered with large stipules and stinging hairs. Leaves alternate, clustered at the end of branches, simple; stipules free, lateral, ovate to almost round, 1–2.5 cm × 1–2 cm, apex acute to acuminate, glabrous or ciliate, green, persistent; petiole 8–16 cm long, pubescent, with many stinging hairs up to 2.5 mm long; blade ovate, lobed or divided, rarely entire, 6–25 (–36) cm × (5–)15–25(–30) cm, base deeply cordate, lobes triangular and unlobed to lobed, acuminate at the apex, margin toothed, upper surface with short hairs and scattered stinging hairs, lower surface densely hairy and with scattered stinging hairs on the veins, mineral concretions visible from above in the form of dots, lateral veins in 5–7 pairs. Inflorescence an axillary panicle up to 30 cm long, much branched, with flowers in small clusters at the branching points or scattered along the axes, pubescent and with many stinging hairs, rarely persisting after leaves have fallen, peduncle c. 5 cm long, male inflorescence much smaller than the female. Flowers unisexual, yellow-green; male flowers regular, 5-merous, almost sessile, perianth globular and up to 2 mm in diameter, rudimentary ovary present; female flowers 4-merous, almost sessile, yellow, perianth up to 1 mm in diameter, outer pair of tepals smaller than inner pair, both pairs becoming thinly membranous, ovary superior, ovoid, staminodes absent. Fruit an achene 1–1.5 mm long, compressed, enc1osed in the persistent membranous perianth.
In Kenya Obetia radula flowers in February–April and September–December.
Obetia comprises 8 species, distributed in eastern Central Africa, East Africa, southern Africa and the Indian Ocean islands, mostly in dry habitats. The bark of Obetia madagascariensis (Poir.) Wedd., a shrub or small tree endemic to western and southern Madagascar, also yields an excellent fibre. It was formerly used for making fishing lines, but has been replaced by nylon fibre. The leaf is used for treatment of eye diseases.
Obetia radula occurs from sea level up to 2000 m altitude, on rocky slopes in evergreen or semi-evergreen bushland, sometimes on rocky shores of lakes and rivers and at the margin of dry montane forest.
In Madagascar Obetia radula is planted around houses and conserved when land is cleared; it can be thus be found in villages and in hedges around fields.
Genetic resources and breeding
In view of its fairly wide distribution, Obetia radula does not seem in danger of genetic erosion.
Obetia radula is a useful local source of fibre and traditional medicines. Detailed information on the fibre and pharmacological 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.
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Correct citation of this article:
Brink, M., 2009. Obetia radula (Baker) B.D.Jacks. In: Brink, M. & Achigan-Dako, E.G. (Editors). Prota 16: Fibres/Plantes à fibres. [CD-Rom]. PROTA, Wageningen, Netherlands.