Brachystegia nigerica (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Cereal / pulse|
Brachystegia nigerica Hoyle & A.P.D.Jones
- Protologue: Kew Bull. 1947(1): 68 (1947).
- Family: Caesalpiniaceae (Leguminosae - Caesalpinioideae)
Origin and geographic distribution
Brachystegia nigerica is endemic to southern Nigeria.
The wood, traded together with some other Brachystegia species as ‘okwen’ or ‘naga’, is used for low-quality furniture and tool handles. It is suitable for light construction, flooring, joinery, interior trim, ship building, vehicle bodies, boxes, crates, food containers, toys, novelties, veneer and plywood.
Flour made from the seeds is used as thickening and flavouring agent in soup preparation. In traditional medicine, leaf and bark extracts are used in the treatment of stomach disorders, fever, urinary infections and gonorrhoea.
Production and international trade
The wood of Brachystegia nigerica is mainly used and traded locally. It is probably occasionally exported in mixed consignments.
The heartwood is pale brown to dark brown and distinctly demarcated from the whitish to pale yellowish brown, up to 15 cm wide sapwood. The grain is often wavy or interlocked, texture moderately coarse to coarse. Quarter-sawn surfaces often show a stripe or roe figure.
The wood is medium-weight, with a density of 675–705 kg/m³ at 12% moisture content, and moderately hard. It air dries slowly but fairly well. Kiln drying should be done slowly and carefully because there is a risk of deep surface checks. End splitting can be minimized by applying a bituminous coating to cross-cut ends of boards. Small splits tend to enlarge as drying progresses. Collapse is common in tension wood. The wood has a tendency to bow, cup and spring. The rates of shrinkage are moderate.
At 12% moisture content, the modulus of rupture is 75–105 N/mm², modulus of elasticity 8800–11,300 N/mm², compression parallel to grain 38–57 N/mm², shear 10.5–18.5 N/mm², cleavage 18 N/mm and Janka side hardness 5420–6360 N.
The wood works fairly well with machine tools, but with serious blunting effect on saw teeth and cutting edges and a risk of overheating during sawing. It is difficult to work with hand tools. During planing, there is a tendency of tearing when interlocked grain is present; a reduced cutting angle of 10–13° should be used for best results. The wood is liable to splitting upon nailing, and pre-boring is recommended. The wood is moderately durable, being susceptible to blue stain and insect attacks.
Seed of Brachystegia nigerica yields about 7.3% of a fixed oil on dry weight basis. Per 100 g, the oil contained 84 g of mixed fatty acids; the iodine number is 10.82 and the saponification equivalent 342.5. The essential oil from the leaves is reported to contain α-pinene (17.7%), β-selinene (12.5%) and α-gurjunene (8.8%).
- Evergreen medium-sized to large tree up to 40(–45) m tall; bole branchless for up to 15 m, straight and cylindrical, up to 120 cm in diameter, with or without buttresses; bark surface smooth in young trees, becoming rough and scaly, flaking off in large scales, brown with reddish patches, inner bark fibrous, hard, pinkish, turning brown on exposure; crown spreading, dense; twigs glabrous.
- Leaves alternate, paripinnately compound with (3–)5–9 pairs of leaflets; stipules 1–2 cm long, caducous; petiole c. 0.5 cm long, swollen at the base, grooved above, rachis 3.5–11 cm long, narrowly winged; leaflets opposite, obliquely elliptical to obovate or oblong, 0.5–7.5 cm × 0.3–3.5 cm, becoming larger towards the apex of rachis, nearly glabrous, pinnately veined with up to 14 pairs of lateral veins.
- Inflorescence a terminal panicle up to 3.5 cm long, short-hairy, densely flowered.
- Flowers bisexual, nearly regular, small, fragrant, at base with 2 ovate bracteoles c. 6 mm long; pedicel 3–5 mm long; sepals (3–)5, slightly unequal, 2–2.5 mm long, nearly glabrous; petals absent; stamens 10, nearly free, c. 1 cm long; ovary superior, ellipsoid, c. 3 mm long, with c. 3 mm long stipe, hairy, style slender, c. 1 cm long.
- Fruit an oblong to obovoid, flattened pod 9–15(–17) cm × 3.5–5 cm, at a right angle to the stipe, smooth but slightly wrinkled, dark purplish brown or nearly black when ripe, dehiscent with 2 woody valves, usually 4-seeded.
- Seeds disk-shaped, c. 2 cm in diameter, dark brown.
Citation correcte de cet article
Brachystegia nigerica, especially mature trees, may be recognized by its small leaflets diminishing in size from the apex downwards. In young trees, the grooved and narrowly winged petiole distinguishes it from the other Brachystegia species in its range. Trees usually flower in December. Fruits ripen in October–December, but have also been recorded in June. They open explosively, dispersing the seeds over short distances.
Brachystegia is a taxonomically difficult genus comprising about 30 species, distributed in mainland tropical Africa and South Africa, the majority of species occurring in southern tropical Africa, where they are characteristic of miombo woodland.
Brachystegia kennedyi Hoyle is a medium-sized to large tree up to 45(–50) m tall with bole up to 220 cm in diameter and often large buttresses. It occurs, sometimes gregariously, in evergreen forest in Nigeria and western Cameroon, and differs from Brachystegia nigerica mainly in its leaves which have generally larger leaflets with apical leaflets slightly smaller than middle ones. The brownish wood, also traded as ‘okwen’ or ‘naga’, is moderately tough and durable, and suitable for construction work and joinery, having fairly good machining properties.
Brachystegia nigerica occurs in lowland rainforest, especially in wetter parts along watercourses, where it may grow gregariously. It is also reported from deciduous woodland and hill slopes.
Brachystegia nigerica can be managed by coppicing. Logs may have brittle heart, requiring caution during harvesting. It is necessary to treat freshly felled logs with preservatives or to process them immediately to prevent blue stain attack. Freshly harvested logs do not float in water and cannot be transported by river.
Brachystegia nigerica has a limited distribution area and occurs in small populations. It is not common and is likely to suffer from genetic erosion, requiring conservation measures. It is classified as vulnerable in the IUCN Red List of threatened species.
Brachystegia nigerica will only remain useful tree for domestic use of the edible seeds and in traditional medicine. Its prospects as a timber tree seem small, even for the local market, due to its limited occurrence. The focus of research should be towards its conservation and sustainable management.
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- E.A. Obeng, Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
Correct citation of this article
Obeng, E.A., 2012. Brachystegia nigerica Hoyle & A.P.D.Jones. [Internet] Record from PROTA4U. Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 14 February 2019.
- See the Prota4U database.