Prota 7(2): Timbers/Bois d’œuvre 2
Fl. W. trop. Afr. 1(2): 464 (1928).
Origin and geographic distribution
Octoknema borealis occurs from Guinea to Ghana.
The wood is used locally, mainly for making frames in the construction of huts and for reinforcement of the mudwalls. It is also used as firewood. The pulverized bark is rubbed on the skin as a treatment for fever. The bark is steeped in cold water and the resulting infusion is drunk to cure cough.
The heartwood is yellow to pale brown and not distinctly demarcated from the sapwood. The wood is fairly hard and strong; it has a glossy lustre. It is medium-weight, with a density of 650–800 kg/m³ at 12% moisture content. At the same moisture content, the modulus of rupture is 127 N/mm², modulus of elasticity 16,760 N/mm² and Janka side hardness 6000 N. The wood cuts easily, but has a tendency to pick up on planing. However, it can be finished to a smooth surface. It is fairly durable.
Dioecious, medium-sized tree up to 30 m tall; bole straight, cylindrical or slightly uneven, up to 60 cm in diameter, with buttresses; bark surface slightly rough, flaky, inner bark cream-coloured to pale yellow, often with irregular orange stripes, fibrous; crown dense, consisting of long branches; twigs and leaves with persistent scurfy, stellate hairs. Leaves alternate, simple and entire; stipules absent; petiole up to 3 cm long, swollen at apex; blade oblong to obovate, often slightly asymmetric, 8–30 cm × 3–13 cm, cuneate at base, acuminate at apex, pinnately veined with 6–10 pairs of distinct lateral veins. Inflorescence an axillary spike-like raceme; male inflorescence 5–8 cm long, many-flowered, female one shorter, few-flowered. Flowers unisexual, regular, usually 5-merous; pedicel 1–3 mm long, pubescent; perianth lobes up to 2.5 mm long, yellow, stellate hairy; male flowers with stamens opposite perianth lobes, c. 1.5 mm long; female flowers with inferior ovary, 1-celled, style very short, 3–5-lobed with bifid lobes. Fruit a nearly globose drupe up to 1.5 cm long, orange when ripe, hairy, with persistent perianth lobes at apex, 1-seeded. Seedling with epigeal germination; hypocotyl 8–10 cm long, epicotyl c. 1 cm long; cotyledons leafy, ovate-elliptical, c. 5 cm × 2.5 cm.
Octoknema borealis flowers from November till April and ripe fruits can be found from January to June.
Octoknema comprises about 6 species and has been frequently placed in a separate family Octoknemataceae, but it is now generally accepted as belonging to Olacaceae.
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 2: growth ring boundaries indistinct or absent. Vessels: 5: wood diffuse-porous; (12: solitary vessel outline angular); 14: scalariform perforation plates; 15: scalariform perforation plates with ≤ 10 bars; 16: scalariform perforation plates with 10–20 bars; 21: intervessel pits opposite; (22: intervessel pits alternate); (26: intervessel pits medium (7–10 μm)); 27: intervessel pits large (≥ 10 μm); 32: vessel-ray pits with much reduced borders to apparently simple: pits horizontal (scalariform, gash-like) to vertical (palisade); 41: mean tangential diameter of vessel lumina 50–100 μm; (48: 20–40 vessels per square millimetre); 49: 40–100 vessels per square millimetre. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; (65: septate fibres present); 66: non-septate fibres present; 69: fibres thin- to thick-walled. Axial parenchyma: 75: axial parenchyma absent or extremely rare; 93: eight (5–8) cells per parenchyma strand. Rays: 97: ray width 1–3 cells; (98: larger rays commonly 4- to 10-seriate); (107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells); 108: body ray cells procumbent with over 4 rows of upright and/or square marginal cells; 115: 4–12 rays per mm; 116: ≥ 12 rays per mm. Mineral inclusions: 136: prismatic crystals present; 140: prismatic crystals in chambered upright and/or square ray cells.
(E. Uetimane, P.E. Gasson & E.A. Wheeler)
Octoknema borealis is found in evergreen and semi-deciduous forest. In Ghana it is most common on moister forest slopes.
Octoknema borealis regenerates in the shade; it is classified as a shade bearer.
Genetic resources and breeding
Octoknema borealis is fairly common in many regions within its distribution area. As the wood of is not much sought after yet, the main threat could come from increased demand for medicinal purposes.
Although the wood of Octoknema borealis has favourable properties, too little information is available to properly evaluate its prospects for increased use as a source of timber. However, the comparatively small size of the tree limits its applications, remaining particularly useful for the construction of local houses. The fact that it is available in moderate volumes demands more research into its industrial use.
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Correct citation of this article:
Bosch, C.H., 2010. Octoknema borealis Hutch. & Dalziel. In: Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). Prota 7(2): Timbers/Bois d’œuvre 2. [CD-Rom]. PROTA, Wageningen, Netherlands.
wood in transverse section
wood in tangential section
wood in radial section