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Pterocarpus osun Craib

Protologue
Bull. Misc. Inform. Kew 1910: 329 (1910).
Family
Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
Origin and geographic distribution
Pterocarpus osun is endemic to southern Nigeria, Cameroon and Equatorial Guinea.
Uses
The bole is used to make dugout canoes and the wood for carpentry, drums and walking sticks. The reddish sap from the bark is used for dyeing, e.g. of traditional sculptures. The stem is an ingredient of traditional medicines against sickle-cell disorder and amenorrhoea. Powdered stem is applied topically to treat skin diseases, to prevent infections of the freshly severed umbilical cord, to treat stiff joints, sprains and rheumatic complaints, and to promote healing of fractured bones.
Production and international trade
The wood is traded in small quantities, occasionally in mixed consignments with other Pterocarpus spp. as ‘African padauk’.
Properties
The heartwood is dull red and fairly hard. It nails well and is liable to termite attack. It contains red pigments of the santarubin and santalin groups. Santalins can be used as histological stain. The seeds contain 28% crude protein, but in tests with rats their nutritive value was inferior to casein. Before they can be used as food components or feed supplements, safety studies and methods of proper processing to remove antinutritional factors and possible toxic constituents are required. The seed oil has been identified as a useful source of vitamin A activity based on its β-carotene content. Its main fatty acids are linoleic acid, oleic acid, palmitic acid and behenic acid. In-vitro antimicrobial properties of the stem have been demonstrated. Stem extracts showed antioxidant activity, and could induce a depigmenting effect and replace synthetic cosmetic formulations.
Botany
Evergreen or deciduous small to medium-sized tree up to 30 m tall but usually much smaller; bole often short and crooked, up to 80(–170) cm in diameter, sometimes with small buttresses at base; bark surface brown, rough, flaking off in irregular patches, inner bark yellowish, exuding a reddish gum on slashing; crown spreading; twigs densely brown short-hairy when young, with soft prickles. Leaves alternate, imparipinnately compound with (9–)10–18 leaflets; stipules 7–15 mm long, falling off early; petiole (3–)4.5–6(–8.5) cm long, rachis (9–) 13–20(–26) cm long, densely brown hairy; petiolules 3–6 mm long; leaflets alternate to almost opposite, oblong to ovate or obovate, (4–)6–13 cm × 2–5 cm, base rounded or slightly cordate, apex shortly acuminate, papery, densely hairy below when young but later glabrescent, with 7–11 pairs of lateral veins. Inflorescence an axillary or terminal panicle (4–)8–22 cm long, densely brown hairy. Flowers bisexual, papilionaceous; pedicel c. 2 mm long; calyx campanulate, c. 7 mm long, densely hairy, with 5 triangular teeth 1.5–3.5 mm long, upper 2 slightly longer than lower 3; corolla with clawed petals, yellow, standard obovate, up to 14 mm × 12 mm, wings up to 12 mm long, keel up to 10 mm long; stamens 10, fused into a sheath up to 8 mm long, the upper stamen sometimes partly free; ovary superior, stiped, hairy, style up to 2.5 mm long, glabrous. Fruit an orbicular, flattened, indehiscent pod 7.5–15 cm in diameter, on a stipe up to 1.5 cm long and with a papery, wavy wing, brown hairy and with prickles, 1-seeded. Seed kidney-shaped, 18–24 mm × c. 12 mm, dark brown to blackish.
In Nigeria trees flower in August–November when they are in full leaf. Bees commonly visit the flowers and probably act as pollinators. The roots have nodules containing nitrogen-fixing bacteria.
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.
Ecology
Pterocarpus osun occurs in lowland evergreen or deciduous forest.
Genetic resources and breeding
Pterocarpus osun has a limited area of distribution where it seems to occur scattered, and consequently may be easily liable to genetic erosion.
Prospects
Pterocarpus osun has been studied insufficiently, and it is difficult to determine its prospects as a commercial timber tree under sustainable management. Its often poorly shaped bole is a serious drawback. Its medicinal properties are promising for the development of skin care products.
Major references
• Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
• Ebi, G.C. & Ofoefule, S.I., 2000. Antimicrobial activity of Pterocarpus osun stems. Fitoterapia 71(4): 433–435.
• Keay, R.W.J., 1989. Trees of Nigeria. A revised version of Nigerian trees (1960, 1964) by R.W.J. Keay, C.F.A. Onochie and D.P. Stanfield. Clarendon Press, Oxford, United Kingdom. 476 pp.
• Rojo, J.P., 1972. Pterocarpus (Leguminosae-Papilionaceae) revised for the world. Phanerogamarum Monographiae. Volume 5. J. Cramer, Lehre, Germany. 119 pp.
Other references
• Avwioro, O.G., Aloamaka, P.C., Ojianya, N.U., Oduola, T. & Ekpo, E.O., 2005. Extracts of Pterocarpus osun as a histological stain for collagen fibres. African Journal of Biotechnology 4(5): 460–462.
• Ezeagu, I.E., Petzke, K.J., Lange, E. & Metges, C.C., 1998. Fat content and fatty acid composition of oils extracted from selected wild-gathered tropical plant seeds from Nigeria. Journal of the American Oil Chemists’ Society 75(8): 1031–1035.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Olukemi, O.A., Oluseyi, J.M., Olukemi, I.O. & Olutoyin, S.M., 2005. The use of selected Nigerian natural products in management of environmentally induced free radical skin damage. Pakistan Journal of Biological Sciences 8(8): 1074–1077.
• Proll, J., Petzke, K.J., Ezeagu, I.E. & Metges, C.C., 1998. Low nutritional quality of unconventional tropical crop seeds in rats. Journal of Nutrition 128(11): 2014–2022.
• Sprent, J.I., 2001. Nodulation in legumes. Royal Botanic Gardens, Kew, United Kingdom. 146 pp.
Author(s)
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
D. Louppe
CIRAD, Département Environnements et Sociétés, Cirad es-dir, Campus international de Baillarguet, TA C-DIR / B (Bât. C, Bur. 113), 34398 Montpellier Cedex 5, France
A.A. Oteng-Amoako
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
J.R. Cobbinah
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article:
Lemmens, R.H.M.J., 2008. Pterocarpus osun Craib. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.