Prota 7(2): Timbers/Bois d’œuvre 2
Engl. & Prantl, Nat. Pflanzenfam. III, 3: 386 (1894).
Caesalpiniaceae (Leguminosae - Caesalpinioideae)
Origin and geographic distribution
Hylodendron gabunense occurs from southern Nigeria to south-western DR Congo.
The wood, known as ‘mvanda’ in Cameroon and ‘mvana’ in Gabon, is used for joinery and tool handles. It is suitable for heavy construction, heavy flooring, interior trim, ship building, vehicle bodies, mine props, furniture, sporting goods, toys, novelties, agricultural implements, railway sleepers, carvings and turnery.
In traditional medicine the bark is used as antidote against poisoning and as a mouthwash to treat toothache. Bark decoctions are administered to treat sterility in women and to induce labour, as aphrodisiac, and also against infections of the respiratory tract and venereal diseases.
The heartwood is yellowish white to pale brown, sometimes with a pink tinge, and is not distinctly demarcated from the sapwood. The grain is straight, texture moderately fine.
The wood is heavy, with a density of about 900 kg/m³ at 12% moisture content. The rates of shrinkage upon air drying are high, from green to oven dry 5.9% radial and 10.3% tangential. At 12% moisture content, the modulus of rupture is 244 N/mm², modulus of elasticity 17,440 N/mm², compression parallel to grain 91 N/mm², shear 10.5 N/mm², cleavage 17 N/mm and Chalais-Meudon side hardness 8.4.
With appropriate equipment, the wood saws fairly well despite its hardness. It has been recommended to quarter-sawn the timber before further processing. Machining and planing show good results with a nice finish. The wood has good nailing properties, but pre-boring is needed. It is moderately durable, being moderately resistant to termite and pinhole borer attacks, but susceptible to Lyctus and marine borers. It is resistant to impregnation with preservatives.
The presence of tannins has been recorded for bark and roots. From an aqueous leaf extract 1,3,4,5-tetragalloylapiitol has been isolated. This compound was found to be a potent inhibitor of HIV RNase H enzymatic activity in vitro.
Medium-sized to fairly large tree up to 40(–55) m tall; bole branchless for up to 25 m, straight and cylindrical, up to 100(–150) cm in diameter, with many, thin and often branched buttresses, in young trees bole with spines; bark surface smooth, pale grey to greenish yellow, on buttresses often with horizontal grooves, inner bark thin, fibrous, pinkish to brown, with little reddish exudate; twigs short-hairy. Leaves alternate, imparipinnately compound with 8–15 leaflets; stipules large and sheath-like, 2–6 cm × c. 0.5 cm, caducous, leaving conspicuous circular scars; petiole and rachis together 5–18 cm long; petiolules 3–4 mm long; leaflets alternate, oblong-lanceolate to oblong-elliptical, 4–15 cm × 1.5–5.5 cm, acuminate at apex, glabrous, with some translucent dots, pinnately veined with up to 20 pairs of lateral veins connected into a marginal vein. Inflorescence an axillary or terminal panicle 4–8 cm long, short-hairy; bracts broadly ovate, up to 1 cm in diameter. Flowers bisexual, slightly zygomorphic; pedicel 3–5 mm long; sepals 4, free, slightly unequal, ovate to lanceolate, 4–5 mm long, whitish to pinkish; petals absent; stamens 10, free, 5–8 mm long; ovary superior, sessile, c. 3 mm long, glabrous, 1-celled, style c. 3 mm long. Fruit an oblong to narrowly obovate papery pod 6–12 cm × 1.5–3.5 cm, reticulately veined, indehiscent, 1(–4)-seeded in apical part of fruit. Seed smooth, brown, with hard seed coat. Seedling with epigeal germination; hypocotyl 3.5–5 cm long, epicotyl 4–5.5 cm long; first leaves alternate, with 1–2 pairs of leaflets.
The mean annual growth in bole diameter of Hylodendron gabunense trees in natural forest has been estimated at 3–4 mm. Young foliage is pinkish. In Gabon fruits are produced in December to February. They are dispersed by wind over distances of sometimes over 200 m. The fruits are eaten by rodents and, especially in times of fruit scarcity, by gorillas. Seedlings are often quite abundant in the forest.
Hylodendron comprises a single species. It is classified in the tribe Detarieae, in which its position is still unresolved.
Hylodendron gabunense occurs in lowland rainforest, where it is usually found scattered, but it may occur in small groups in secondary forest and formerly cultivated land.
In Cameroon the average number of trees with a bole diameter above 15 cm has been estimated at 0.6 per ha, with an average wood volume of 1.1 m³/ha. The average wood volume in Gabon has been estimated at 0.3 m³/ha. The wood volume of a bole 23 m long and 76 cm in diameter was 6.7 m³.
Genetic resources and breeding
Hylodendron gabunense is not threatened by genetic erosion because it is fairly widespread and is commonly found in secondary forest.
With its rather low growth rates resulting in hard and heavy wood, the prospects of Hylodendron gabunense as a timber tree of commercial importance are probably limited. It may remain of local importance, especially for heavy construction.
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Correct citation of this article:
Lemmens, R.H.M.J., 2010. Hylodendron gabunense Taub. 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.