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Hexalobus crispiflorus A.Rich.

Hist. phys. Cuba, Pl. vasc. 1: 43 (1845).
Origin and geographic distribution
Hexalobus crispiflorus occurs from Guinea Bissau east to southern Sudan, and south to Gabon and DR Congo.
The wood, known as ‘owui’ in Cameroon and Gabon and as ‘duabaha’ in Ghana, is used for house construction, joinery, knife-handles, gun-butts, paddles and shingles. It is suitable for flooring, interior trim, ship building, vehicle bodies, furniture, cabinet work, mine props, sporting goods, toys, novelties, agricultural implements, boxes, crates, vats, turnery, hardboard, particleboard and pulpwood.
The fruit is edible; it is eaten fresh. The outer part of the pulp is firm and has a slightly tart taste, the inner part surrounding the seeds is jelly-like and sweet. The inner bark is used as a masticatory together with kola nut. Bark decoctions are used in a bath to treat fever and skin troubles. A bark macerate is taken to treat venereal diseases, and pulped bark is applied to wounds, furuncles and swollen glands. A decoction of the twig bark is drunk as emetic and purgative. In Cameroon the bark is used to treat gonorrhoea and syphilis. In Sierra Leone the bark is stripped off from young trees and used as fibre.
Production and international trade
The wood is not traded on the international market and only used domestically. The stem bark is sometimes traded on local markets. In 2002 in markets in Yaoundé (Cameroon) 1 kg of bark was sold at a price of 3000 FCFA.
The heartwood is pale yellow to pinkish or pale brown and not distinctly demarcated from the sapwood. The grain is straight, texture fine. The wood is slightly streaked on quarter-sawn and backsawn surfaces, and is lustrous.
The wood is medium-weight, with a density of 530–600 kg/m³ at 12% moisture content. The rates of shrinkage during drying are moderate. At 12% moisture content, the modulus of rupture is 94–111 N/mm², compression parallel to grain 49–53 N/mm², cleavage 18–22.5 N/mm and Chalais-Meudon side hardness 1.8–2.4.
The wood works readily with both hand and machine tools, but is difficult to saw and peel because of the sinuous and strongly fluted logs. It planes well and takes a nice polish. The wood seems to have fair nailing properties. It is moderately durable. It shows some resistance to attacks by termites and marine borers, but is susceptible to Lyctus attack. The heartwood is resistant to impregnation with preservatives, the sapwood moderately resistant.
Bark, wood and leaves contain alkaloids, with the bark having the highest concentration (0.64% on a dry weight basis). An essential oil was isolated from the bark; this oil has a high sesquiterpene content (99.5%). The oil showed distinct activity against the W2 strain of Plasmodium falciparum. Nerolidol, which is present in the oil at a concentration of about 3%, may be partly responsible for the antiplasmodial activity. Diprenylated indoles, called hexalobines, with significant antifungal activity, have been isolated from the bark.
Small to medium-sized tree up to 30 m tall; bole branchless for up to 15(–27) m, often sinuous, up to 100(–140) cm in diameter, strongly fluted; bark surface longitudinally fissured and becoming scaly with small elongate scales, greyish brown, inner bark soft, fibrous and yellowish turning orange upon exposure, slightly scented; crown rounded, with ascending branches; twigs short-hairy to nearly glabrous. Leaves alternate and distichous, simple and entire; stipules absent; petiole 3–6 mm long; blade elliptical to ovate-lanceolate, 7.5–23 cm × 3–8 cm, obtuse to rounded and slightly asymmetrical at base, acuminate at apex, papery to thin-leathery, usually short-hairy below, pinnately veined with 12–18 pairs of lateral veins. Inflorescence an axillary fascicle of 1–3 flowers. Flowers bisexual, regular, 3-merous; pedicel 0.5–1.5 cm long; sepals free, ovate to elliptical-ovate, 1–2 cm long, reflexed, hairy; petals in 2 whorls, narrowly oblong, 2.5–8.5 cm long, fused at base, crispy at margins, short-hairy, pale yellow; stamens numerous, with short filaments and oblong-linear anthers 3–4 mm long; carpels 7–10, 4–5 mm long, ovaries oblong, hairy, stigmas 2-lobed. Fruit consisting of up to 4 indehiscent, oblong follicles 8–9 cm × 4–5 cm, finely wrinkled and rusty brown hairy, many-seeded. Seeds flattened-ellipsoid, 3–4 cm long. Seedling with epigeal germination; hypocotyl 10–12 cm long, epicotyl 2–3 cm long; cotyledons leafy, broadly elliptical, c. 4 cm × 2 cm; first leaves alternate.
Other botanical information
Hexalobus comprises 4 species and is confined to mainland tropical Africa. It is most closely related to Uvariastrum and Asteranthe.
Hexalobus salicifolius Engl. closely resembles Hexalobus crispiflorus, differing in usually smaller leaves and smaller fruits. It is a medium-sized tree up to 35 m tall with bole up to 100 cm in diameter, and has been recorded from Cameroon, Equatorial Guinea and Gabon, and doubtfully from Côte d’Ivoire. It is undoubtedly used for similar purposes as Hexalobus crispiflorus.
Growth and development
Growth of Hexalobus crispiflorus seems to be rather slow. A tree planted in DR Congo did not yet flower 8 years after planting. In Côte d’Ivoire trees flower in April–May and in September.
Hexalobus crispiflorus occurs usually scattered in dense, humid, mainly semi-deciduous forest. It is most common in undisturbed forest. It is often found along rivers, and can penetrate savanna regions through gallery forest. It prefers deep, well-drained soils with good water-retaining capacity.
Propagation and planting
Artificial propagation is only done by seed. One kg contains about 600 seeds. Germination starts 1–3 months after sowing, and the germination rate is about 80%. Seedlings seem to require partial shade for good growth and survival. Planting distance should be up to 6 m × 6 m.
Hexalobus crispiflorus usually occurs in low densities in the forest. In Cameroon, an average density of 0.14 bole of more than 15 cm in diameter per ha has been recorded, with an average wood volume of 0.5 m³/ha. In Gabon the average wood volume is 0.8 m³/ha. In Ghana a minimum bole diameter of 70 cm has been recommended for felling.
A bole harvested in DR Congo of 27 m long and 140 cm in diameter yielded 26.5 m³ of wood.
Genetic resources
Hexalobus crispiflorus is widespread and does not seem to be in immediate danger of genetic erosion. However, it usually occurs in low densities in the forest and prefers undisturbed forest, which may make it vulnerable with ongoing decline in primary forest area.
Hexalobus crispiflorus is a multipurpose tree with local importance for people living in or close to the forest. It yields not only wood, but also edible fruits and products used in traditional medicine. Its importance as a commercial timber tree is limited because of the scattered occurrence in the forest and its poor bole shape. It could be promoted for planting as a fruit tree, but research is needed on propagation methods and proper management of planted trees. The bark seems to have prospects for drug development against malaria.
Major references
• Bolza, E. & Keating, W.G., 1972. African timbers: the properties, uses and characteristics of 700 species. Division of Building Research, CSIRO, Melbourne, Australia. 710 pp.
• Boyom, F.F., Ngouana, V., Zollo, P.H., Menut, C., Bessiere, J.M., Gut, J. & Rosenthal, P.J., 2003. Composition and anti-plasmodial activities of essential oils from some Cameroonian medicinal plants. Phytochemistry 64(7): 1269–1275.
• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 960 pp.
• Danforth, R.M. & Noren, P.D., 1997. Congo native fruits: twenty-five of the best fruits and nuts found in the rainforest and savanna areas of northwest Congo, Africa. Loko AF Program, Bangui, Central African Republic. 72 pp.
• Fouarge, J. & Gérard, G., 1964. Bois du Mayumbe. Institut National pour l’Etude Agronomique du Congo (INEAC), Brussels, Belgium. 579 pp.
• le Thomas, A., 1969. Annonacées. Flore du Gabon. Volume 16. Muséum National d’Histoire Naturelle, Paris, France. 372 pp.
• Oteng-Amoako, A.A. (Editor), 2006. 100 tropical African timber trees from Ghana: tree description and wood identification with notes on distribution, ecology, silviculture, ethnobotany and wood uses. 304 pp.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan. 248 pp.
• Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 pp.
• Vivien, J. & Faure, J.J., 1996. Fruitiers sauvages d’Afrique: espèces du Cameroun. Ministère Français de la Coopération, Paris, France & CTA, Wageningen, Netherlands. 416 pp.
Other references
• Abbiw, D.K., 1990. Useful plants of Ghana: West African uses of wild and cultivated plants. Intermediate Technology Publications, London and Royal Botanic Gardens, Kew, Richmond, United Kingdom. 337 pp.
• Achenbach, H., Renner, C. & Waibel, R., 1995. Constituents of tropical medicinal plants. LXIX. The hexalobines, diprenylated indoles from Hexalobus crispiflorus and Hexalobus monopetalus. Liebigs Annalen der Chemie 1995(7): 1327–1337.
• Aké Assi, L., Abeye, J., Guinko, S., Riguet, R. & Bangavou, X., 1985. Médecine traditionnelle et pharmacopée - Contribution aux études ethnobotaniques et floristiques en République Centrafricaine. Agence de Coopération Culturelle et Technique, Paris, France. 140 pp.
• Aubréville, A., 1959. La flore forestière de la Côte d’Ivoire. Deuxième édition révisée. Tome premier. Publication No 15. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 369 pp.
• Bouquet, A. & Debray, M., 1974. Plantes médicinales de la Côte d’Ivoire. Travaux et Documents No 32. ORSTOM, Paris, France. 231 pp.
• Boutique, R., 1951. Annonaceae. In: Robyns, W., Staner, P., Demaret, F., Germain, R., Gilbert, G., Hauman, L., Homès, M., Jurion, F., Lebrun, J., Vanden Abeele, M. & Boutique, R. (Editors). Flore du Congo belge et du Ruanda-Urundi. Spermatophytes. Volume 2. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 256–389.
• de la Mensbruge, G., 1966. La germination et les plantules des essences arborées de la forêt dense humide de la Côte d’Ivoire. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 389 pp.
• de Saint-Aubin, G., 1963. La forêt du Gabon. Publication No 21 du Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 208 pp.
• Hawthorne, W.D., 1995. Ecological profiles of Ghanaian forest trees. Tropical Forestry Papers 29. Oxford Forestry Institute, Department of Plant Sciences, University of Oxford, United Kingdom. 345 pp.
• Hawthorne, W. & Jongkind, C., 2006. Woody plants of western African forests: a guide to the forest trees, shrubs and lianes from Senegal to Ghana. Kew Publishing, Royal Botanic Gardens, Kew, United Kingdom. 1023 pp.
• Irvine, F.R., 1961. Woody plants of Ghana, with special reference to their uses. Oxford University Press, London, United Kingdom. 868 pp.
• Keay, R.W.J., 1989. Trees of Nigeria. A revised version of Nigerian trees (1960, 1964) by Keay, R.W.J., Onochie, C.F.A. & Stanfield, D.P. Clarendon Press, Oxford, United Kingdom. 476 pp.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Normand, D. & Paquis, J., 1976. Manuel d’identification des bois commerciaux. Tome 2. Afrique guinéo-congolaise. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 335 pp.
• Okpoti-Paulo, N.L.I., 1990. the aetiology of diseases – a traditional view point and the alkaloids of Hexalobus crispiflorus A. Rich. (Annonaceae). B. Pharm. Degree thesis, Department of Pharmacognosy, Faculty of Pharmacy, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. 44 pp.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
• Sallenave, P., 1955. Propriétés physiques et mécaniques des bois tropicaux de l’Union française. Centre Technique Forestier Tropical, Nogent sur Marne, France. 129 pp.
• Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays Bas. pp. 465–1271.
• Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.
Sources of illustration
• Irvine, F.R., 1961. Woody plants of Ghana, with special reference to their uses. Oxford University Press, London, United Kingdom. 868 pp.
• Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.
G.D. Djagbletey
Forestry Research Institute of Ghana, Council for Scientific and Industrial Research, Ghana

R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
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
Associate editors
E.A. Obeng
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
Photo editor
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Djagbletey, G.D., 2011. Hexalobus crispiflorus A.Rich. 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.
Distribution Map wild

1, base of bole; 2, leaf; 3, flowering branch; 4, fruit.
Redrawn and adapted by Achmad Satiri Nurhaman

obtained from W.D. Hawthorne

obtained from W.D. Hawthorne