Prota 7(1): Timbers/Bois d’œuvre 1
Apont.: 584 (1859).
Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
Pterocarpus chrysothrix Taub. (1895), Pterocarpus stolzii Harms (1915).
Tacula (Po). Mninga maji (Sw).
Origin and geographic distribution
Pterocarpus tinctorius is widespread in Central, East and southern Africa, from Congo and DR Congo east to Tanzania and south to Angola, Zambia, Malawi and Mozambique.
The wood is popular for furniture, cabinet making and decorative parquet floors. It is also suitable for light construction, joinery, interior trim, boxes, crates, tool handles, carving, turnery, veneer, plywood, hardboard, particle board, and pulpwood for lower-quality paper production. It is used as firewood and for making charcoal. The foliage is browsed by goats. The reddish dye from the wood has been used for colouring the body. In DR Congo a bark decoction is applied as a rectal washing to treat lung congestion in children. In Tanzania the tree is used for shade.
Production and international trade
The wood is traded on the international market in small quantities. It is occasionally traded in mixed consignments with other Pterocarpus spp. as ‘African padauk’. It is traded from the East Usambara Mountains in Tanzania; in 1990 the local price of a plank of 3.7 m × 0.3 m was approximately US$ 2.40, in 2000 US$ 4. The timber is locally in great demand, e.g. in Burundi and DR Congo from where it is exported.
In general, the properties of Pterocarpus tinctorius are comparable to those of Pterocarpus angolensis DC. The heartwood is pale yellow when freshly cut but turning to pinkish red upon exposure, and distinctly demarcated from the whitish, 7.5–10 cm wide sapwood. The grain is often interlocked, texture moderately fine. Irregular, small, dark red or brown markings are present on tangential surfaces; the wood contains red gummy substances. The density of the wood at 12% moisture content ranges from about 450 kg/m³ (forest trees, Mayombe, DR Congo) to about 900 kg/m³ (savanna trees, Burundi). The wood usually dries well with little deformation. Shrinkage rates from green to oven dry are 3.3% radial and 5.5% tangential for wood from Burundi. Once dry, the wood is stable in service. At 12% moisture content, the modulus of rupture of wood from Mayombe is 91 N/mm², modulus of elasticity 9100 N/mm², compression parallel to grain 45 N/mm², cleavage 8 N/mm² and Chalais-Meudon hardness 2.2. At the same moisture content, the modulus of rupture of wood from Burundi is 147 N/mm², modulus of elasticity 15,000 N/mm² and compression parallel to grain 77 N/mm². The wood saws and works well, and can be planed to a smooth surface. It holds nails and screws well and is generally not liable to splitting, although pre-boring is recommended for timber from Burundi. When a filler is used it finishes well. The wood is moderately durable to durable; the lighter wood is liable to termite attack and slightly liable to Lyctus attack, but heavier wood is not. It is moderately resistant to impregnation with preservatives. The sawdust may cause irritation to workers.
Evergreen or deciduous small to medium-sized tree up to 25 m tall; bole branchless for up to 15 m, often straight and cylindrical, up to 75 cm in diameter; bark surface grey to dark brown, fissured and scaly, inner bark whitish exuding a reddish gum on slashing; crown round or flattened, dense; twigs short-hairy when young. Leaves alternate, imparipinnately compound with (5–)7–11(–15) leaflets; stipules oblong, c. 3 mm long, falling off early; petiole (1–)2–5(–10) cm long, rachis (2.5–)4–20(–30) cm long, densely hairy, glabrescent; petiolules (2–)3–8(–12) mm long; leaflets alternate to almost opposite, oblong to ovate or obovate, (2.5–)4.5–11(–13) cm × (1.5–)2–5(–7) cm, base obtuse to rounded or slightly cordate, apex shortly acuminate, papery to thinly leathery, hairy below when young but later glabrescent, with 6–14 pairs of lateral veins. Inflorescence an axillary or terminal panicle (4–)8–22 cm long, densely hairy. Flowers bisexual, papilionaceous; pedicel 3–7 mm long; calyx campanulate, 5–9 mm long, densely hairy, with 5 triangular teeth 1.5–3 mm long, upper 2 slightly longer than lower 3; corolla with clawed petals, cream-coloured to orange-yellow, standard obovate, up to 18 mm × 13 mm, wings up to 16 mm long, keel up to 13 mm long; stamens 10, fused into a sheath up to 10 mm long, the upper stamen sometimes partly free; ovary superior, 1-celled, stiped, hairy, style up to 5.5 mm long, glabrous towards the top. Fruit an orbicular, flattened, indehiscent pod 5–21 cm in diameter, on a stipe up to 2 cm long, with a thin-leathery wavy wing, hairy, greyish brown or reddish brown, 1-seeded. Seed kidney-shaped to oblong, flat to slightly thickened, 15–25 mm × 8–13 mm, wrinkled, dark brown to blackish.
In DR Congo trees flower in March–May. Bees commonly visit the flowers and probably act as pollinators. The leaves are commonly eaten by colobus monkeys and chimpanzees.
Pterocarpus is a pantropical genus belonging to the tribe Dalbergieae; it comprises approximately 30 species of which about 15 occur in Africa, 10 in America and 5 in Asia. Pterocarpus tinctorius is variable and has been subdivided into several infraspecific taxa; however, these are connected by many intermediates when the whole region of distribution is considered.
Pterocarpus indicus Willd. and Pterocarpus dalbergioides Roxb. ex DC., both from tropical Asia, are planted in Africa as ornamental and roadside trees, the former e.g. in Sierra Leone, Nigeria, Kenya, Tanzania and Mauritius, the latter in Madagascar. Both species are important timber trees in tropical Asia, but are not planted for timber production in Africa. In Mauritius the sap of Pterocarpus indicus is used to relieve toothache and as an antidote for poisoning.
Pterocarpus tinctorius occurs in a wide variety of habitats, from evergreen rainforest to riverine forest and wooded savanna, up to 1800 m altitude, often on rocky hills.
Pterocarpus tinctorius can be propagated by seed and by cuttings. Sometimes wildlings are collected for planting. Trees can be managed by coppicing, pollarding and lopping. In Zambia they are reportedly fire resistant.
Genetic resources and breeding
Pterocarpus tinctorius is widespread and locally common, and consequently does not seem to be threatened by genetic erosion.
Pterocarpus tinctorius is a useful timber tree, providing a fair quality wood that is an interesting substitute for the wood of Pterocarpus angolensis, the latter being subject to unsustainable harvesting in many countries. However, Pterocarpus tinctorius has been studied insufficiently, and it is difficult to determine its prospects as a commercial timber tree under sustainable management. Its other uses should also be considered when planning optimal management.
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Correct citation of this article:
Lemmens, R.H.M.J., 2008. Pterocarpus tinctorius Welw. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.