Prota 7(2): Timbers/Bois d’œuvre 2
Bull. Jard. Bot. Etat 24(4): 348 (1954).
Caesalpiniaceae (Leguminosae - Caesalpinioideae)
2n = 24
Macrolobium coeruleoides De Wild. (1907), Macrolobium coeruleum (Taub.) Harms (1915), Macrolobium dawei Hutch. & Dalziel (1928).
Origin and geographic distribution
Paramacrolobium coeruleum is widespread, from Guinea east to Kenya and south to DR Congo, Tanzania and northern Angola. However, the distribution area is notably discontinuous.
In DR Congo the wood is used for joinery, doors, frames of doors, furniture, railway sleepers and gongs. It is suitable for heavy flooring, interior trim, toys, novelties, turnery, carving, veneer and plywood. Paramacrolobium coeruleum has been used as shade tree in cocoa plantations in Sierra Leone. In Kenya the bark is used as rough fibre. The seeds are used in games.
The heartwood is pale brown to yellowish brown or pinkish brown with darker brown streaks on quarter-sawn surfaces, and usually indistinctly demarcated from the sapwood. The grain is straight to interlocked, texture moderately coarse and even. The wood is moderately heavy, with a density of about 700 kg/m³ at 12% moisture content, and is moderately hard. The rates of shrinkage during drying are high and the wood may develop severe surface splits and cupping, whereas it is susceptible to blue stain attack during drying. The wood saws and works well, is easy to plane and takes a good finish. The gluing and bending properties are satisfactory. The wood is moderately durable, being liable to termite, Lyctus and marine borer attacks.
Several long-chain fatty acids have been isolated from root bark extracts; these acetylenic acids showed inhibitory activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the enzyme responsible for the formation of mevalonate in the rate-determining step of cholesterol biosynthesis.
Evergreen, medium-sized to fairly large tree up to 35(–40) m tall; bole branchless for up to 20 m but often low-branching, straight and cylindrical or irregular, up to 90(–100) cm in diameter, with buttresses; bark surface nearly smooth, but with fine longitudinal grooves and lenticels, becoming flaky, grey-brown, inner bark fibrous, brownish to reddish; crown often long and narrow, often with drooping branches; twigs usually glabrous, with lenticels. Leaves alternate, paripinnately compound with 2–5 pairs of leaflets; stipules fused, up to 1.5 cm long, clasping the twigs, persistent; petiole and rachis together 5–22 cm long, grooved; petiolules 1–4 mm long, twisted; leaflets opposite, elliptical to oblong or lanceolate, 2–15 cm × 1–6 cm, asymmetrical at base, acuminate at apex, thinly leathery, glabrous, pinnately veined with 10–15 pairs of indistinct lateral veins. Inflorescence a terminal, flat-topped panicle 4–8 cm long, usually glabrous. Flowers bisexual, zygomorphic, with 2 bracteoles up to 3.5 cm long at base; pedicel 1.5–3 cm long; sepals 4, 1–1.5 cm long, 1 broader than the other 3 and 2-toothed; petals 5, free, unequal, bluish, upper one largest, up to 4.5 cm × 2.5 cm, lateral 2 up to 3 cm × 2.5 mm, lower 2 minute; stamens 9, fused at base, usually 3 fertile, large, up to 3.5 cm long and 6 rudimentary; ovary superior, linear, 1–1.5 cm long, hairy, with long stipe, 1-celled, style 2–2.5 cm long. Fruit an oblong, flattened pod 8.5–20 cm × 2.5–6 cm, glabrous, dehiscing with 2 spiralling woody valves, 3–8-seeded. Seeds rectangular, flattened, 1.5–2.5 cm × 1–2 cm, glossy dark brown, seed coat hard. Seedling with epigeal germination; hypocotyl 5–12 cm long, epicotyl 4–7 cm long; first 2 leaves opposite, with 2–3 pairs of leaflets.
In the nursery seedlings are about 30 cm tall after 4 months and 60 cm tall after 15 months. In Guinea 6-years-old saplings showed a mean annual height growth of 85–130 cm, but in DR Congo planted trees were only 4.5 m tall after 11 years and had a high mortality. Fruits are eaten by monkeys and large rodents, which may serve as seed dispersers.
Paramacrolobium comprises a single species and seems to be related to Cryptosepalum.
Paramacrolobium coeruleum occurs in lowland rainforest up to 450 m altitude, but also in gallery forest in savanna areas and in wooded savanna.
Seeds can be stored for at least 18 months, when the viability is still about 40%. Pre-treatment of seeds is not needed, but soaking in cold water for 1–2 days or in boiling water for a few minutes accelerates germination. Seedlings should be planted out in the full sun and in fertile soils to obtain good growth. They are planted at a spacing of 3 m × 3 m in pure stands or together with other moderately fast growing timber species.
Genetic resources and breeding
Although Paramacrolobium coeruleum occupies a large distribution area, it is absent in large regions within that area and thus shows a disjunct distribution pattern. It is common in many regions, and there is no reason to consider it threatened by genetic erosion.
Paramacrolobium coeruleum will remain a locally important timber tree, but it is unlikely that it will gain importance for commercial exploitation because in areas where it is common the logs are usually too small and too poorly shaped. However, surprisingly little is known about this widespread tree that may have prospects in agroforestry systems or as timber tree in plantations. Research on propagation and growth rates is recommended.
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Correct citation of this article:
Lemmens, R.H.M.J., 2010. Paramacrolobium coeruleum (Taub.) J.Léonard. 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