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Cylicodiscus gabunensis Harms

Protologue
Engl. & Prantl, Nat. Pflanzenfam., II–IV Nachtr. 1: 192 (1897).
Family
Mimosaceae (Leguminosae - Mimosoideae)
Synonyms
Piptadenia gabunensis (Harms) Roberty (1954).
Vernacular names
Okan, denya, African greenheart (En). Okan, bouémon (Fr).
Origin and geographic distribution
Cylicodiscus gabunensis occurs in the forest zone from Côte d’Ivoire to Gabon and Congo.
Uses
The wood (trade names: okan, denya) is used for heavy construction including marine construction, sluice gates and bridges, heavy flooring, joinery, vehicle bodies, mine props, shipbuilding especially for decking, furniture including garden furniture, sporting goods, agricultural implements, railway sleepers, carving and turning. In Nigeria it is used for making pontoons. It is also used as fuelwood and for charcoal production.
The foliage is browsed by sheep and goats. The bark serves as a soap substitute and as a fish poison.
A bark decoction administered by enema is used to treat stomach-ache, and it is drunk or used in a bath as an anodyne and against vomiting, venereal diseases, malaria, psoriasis and rheumatism. A macerate of the leaves is used against migraine.
Production and international trade
The annual export of okan logs from Gabon averaged 13,600 m³ in 2000–2004. In 2003 Cameroon exported about 70 m³ of okan logs and about 7900 m³ of sawnwood, of which 6000 m³ to Europe; in 2004 it exported about 8500 m³ of okan sawnwood, of which 6700 m³ to Europe.
Properties
The heartwood is yellowish brown, often with a slight green tinge, on exposure darkening to reddish brown with a yellowish or greenish tinge; it is distinctly demarcated from the 5–8 cm thick, pale pink sapwood. The grain is interlocked, texture moderately coarse. The wood is often slightly striped and lustrous, and has an unpleasant smell when freshly cut.
The wood is very heavy and hard. At 12% moisture content, the density is 770–1100 kg/m³. The rates of shrinkage during drying are moderate to high, from green to 12% moisture content 3.0% radial and 3.5% tangential, and from green to oven dry 4.0–7.3% radial and 7.2–10.4% tangential. The wood should be air-dried rather slowly or be carefully kiln-dried, to avoid deformation. After drying, the wood is moderately stable in service.
At 12% moisture content, the modulus of rupture is (82–)129–230 N/mm², modulus of elasticity 14,700–22,600 N/mm², compression parallel to grain 64–108 N/mm², shear 8–22 N/mm², cleavage 12–29 N/mm, Janka side hardness 10,600–12,800 N and Janka end hardness 11,340–13,740 N.
The wood is difficult to saw and work, with some dulling effect on cutting edges, and force is required. Stellite-tipped saws are recommended. It is difficult to obtain a smooth finish because of the interlocked grain. Planing shows best results at a cutting angle of 15°. The wood holds screws and nails well, but pre-boring is needed. The gluing, staining, polishing and painting properties are satisfactory, but for optimal polishing effect the use of a filler is required. Turning gives good results. The wood is not suitable for veneer or plywood production.
The heartwood is very durable. It shows excellent natural resistance to wood decay fungi and is also resistant to dry-wood borer, marine borer and termite attacks. It does not absorb preservatives. The sapwood is liable to fungi and powder-post beetles and should be removed before the wood is processed; it is resistant to impregnation. The resistance to wood-rotting fungi is due to the presence of compounds such as isookanin and okanin.
The intake and digestibility of the foliage is high for goats. Flavonoids, saponins, tannins, polyphenols, coumarins, triterpenes and/or sterols, and reducing sugars were detected in the ethyl acetate extract of the stem bark. The extract also showed antimicrobial activity against, among others, Staphylococcus aureus, Proteus vulgaris and Bacillus cereus. In tests with rats, an ethyl acetate extract of the bark produced significant anti-diarrhoeal effect. The bark showed significant antiplasmodial activity in tests with mice, which supports the use against malaria in traditional medicine.
Adulterations and substitutes
The wood of Cylicodiscus gabunensis is considered a substitute for that of azobé (Lophira alata Banks ex P.Gaertn.) from Africa and greenheart (Chlorocardium rodiei (Schomb.) Rohwer, H.G.Richt. & van der Werff) from tropical America. The timber of Piptadeniastrum africanum (Hook.f.) Brenan is similar and also traded as African greenheart.
Description
Large to very large tree up to 60 m tall; bole straight and cylindrical, branchless for up to 30(–35) m, up to 170(–300) cm in diameter, broadened at base, sometimes with low, thick buttresses or fluted; bark surface with rectangular scales, blackish brown, inner bark creamy to yellow, fibrous, with some viscid, yellowish exudate; crown spreading, hemispherical; twigs glabrous, blackish. Leaves alternate, bipinnately compound with 1–2 pairs of pinnae; stipules absent or early caducous; petiole c. 2 cm long, with gland at apex; leaflets alternate, 5–10 per pinna, with petiolule 2–3 mm long, elliptical to lanceolate, 4–10 cm × 2–5 cm, usually slightly asymmetrical at base, acuminate at apex, glabrous. Inflorescence an axillary or terminal spike-like false raceme up to 15 cm long, hairy, densely flowered. Flowers bisexual, regular, 5-merous; pedicel c. 0.5 mm long; calyx with c. 1.5 mm long tube, toothed, reddish; petals free, oblong to lanceolate, c. 3 mm × 0.5 mm, whitish or yellowish; stamens 10, free, c. 5 mm long; ovary superior, ellipsoid, c. 1.5 mm long, with c. 1 mm long stipe, hairy, style slender. Fruit a flattened linear pod up to 90 cm × 5 cm, reddish brown, scaly, reticulately veined, dehiscent at one side, many-seeded. Seeds oblong, flat, up to 7.5 cm long including the papery wing surrounding the seed, brown. Seedling with epigeal germination but cotyledons remaining within seed coat; hypocotyl c. 1 cm long, epicotyl 5–10 cm long.
Other botanical information
Cylicodiscus comprises a single species and seems to have a rather isolated position.
Anatomy
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 2: growth ring boundaries indistinct or absent. Vessels: 5: wood diffuse-porous; 13: simple perforation plates; 22: intervessel pits alternate; 23: shape of alternate pits polygonal; 25: intervessel pits small (4–7 μm); 26: intervessel pits medium (7–10 μm); 29: vestured pits; 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 42: mean tangential diameter of vessel lumina 100–200 μm; 43: mean tangential diameter of vessel lumina 200 μm; 46: 5 vessels per square millimetre; 47: 5–20 vessels per square millimetre; 58: gums and other deposits in heartwood vessels. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 69: fibres thin- to thick-walled; (70: fibres very thick-walled). Axial parenchyma: 79: axial parenchyma vasicentric; 80: axial parenchyma aliform; 81: axial parenchyma lozenge-aliform; (83: axial parenchyma confluent); 91: two cells per parenchyma strand; 92: four (3–4) cells per parenchyma strand. Rays: (97: ray width 1–3 cells); (98: larger rays commonly 4- to 10-seriate); 104: all ray cells procumbent; 115: 4–12 rays per mm. Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells.
(N.P. Mollel, P. Détienne & E.A. Wheeler)
Growth and development
Seedlings tolerate shade, and young trees can be found in small gaps in the forest. The boles of young trees are spiny. The trees are deciduous or evergreen. Adult trees have huge crowns that spread in the upper canopy of the forest. Young leaves are red. In Gabon trees flower in November–April and fruits mature in May–August. In Nigeria trees flower in February–April and June–September, whereas fruiting trees have been observed in November–March. In Ghana fruits are ripe in January–February and May–June. The winged seeds are dispersed by wind. They are eaten by several primate species. Natural regeneration is often sparse.
Ecology
Cylicodiscus gabunensis can be found in deciduous as well as evergreen forest, but is most abundant in well-drained sites in moist semi-deciduous forest. In Gabon it occurs scattered in primary forest, but may be locally more abundant in old secondary forest.
Propagation and planting
The 1000 seed weight is about 100 g. The seeds do not show dormancy, and germinate in 5–12 days. Wildlings are collected for planting.
Management
In general Cylicodiscus gabunensis occurs scattered and in low densities in the forest. In Gabon the average bole volume is 0.3 m³/ha, but in south-western Cameroon 2.1 m³/ha for bole diameters over 60 cm. In Ghana the average stock is estimated at 267 m³/km², and the total exploitable volume (above 70 cm bole diameter) 866,400 m³ with an annual allowable cut volume of 21,600 m³.
Harvesting
Felling of the trees is difficult because the hard wood has a serious dulling effect on saws.
Yield
One big tree may provide 15–20 m³ of usable timber.
Handling after harvest
Logs are durable and can be left in the forest for some time before transport. However, if they are left for a long time, deep splits develop on exposed transverse sections, which extend into the log. The logs sink in water and therefore cannot be transported by river.
Genetic resources
Cylicodiscus gabunensis is fairly widespread in West and Central Africa, the export volumes are low, and it is not commonly cut for local applications because of the hardness of the wood. Therefore, it does not seem to be threatened at present.
Prospects
There is an export market for the naturally durable timber of Cylicodiscus gabunensis. It may replace other durable timbers which have become rare due to overexploitation, such as Milicia species. However, although there is a lack of data, Cylicodiscus gabunensis probably grows slowly, and this may hamper its sustainable exploitation from natural forest.
Major references
• ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.
• 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.
• CIRAD Forestry Department, 2003. Okan. [Internet] Tropix 5.0. http://tropix.cirad.fr/ afr/okan.pdf. Accessed April 2007.
• CTFT (Centre Technique Forestier Tropical), 1955. Okan (Adoum). Bois et Forêts des Tropiques 43: 11-14.
• Déon, G., Chadenson, M. & Hauteville, M., 1980. Influence des extraits naturels du bois sur sa résistance à la pourriture. Bois et Forêts des Tropiques 191: 75–90.
• Farmer, R.H., 1972. Handbook of hardwoods. 2nd Edition. Her Majesty’s Stationery Office, London, United Kingdom. 243 pp.
• Okokon, J.E., Ita, B.N. & Udokpoh, A.E., 2006. Antiplasmodial activity of Cylicodiscus gabunensis. Journal of Ethnopharmacology 107(2): 175–178.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.
• Villiers, J.-F., 1989. Leguminosae - Mimosoideae. Flore du Gabon. Volume 31. Muséum National d’Histoire Naturelle, Paris, France. 185 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.
Other references
• Adjanohoun, E.J., Ahyi, A.M.R., Aké Assi, L., Baniakina, J., Chibon, P., Cusset, G., Doulou, V., Enzanza, A., Eymé, J., Goudoté, E., Keita, A., Mbemba, C., Mollet, J., Moutsamboté, J.-M., Mpati, J. & Sita, P. (Editors), 1988. Médecine traditionnelle et pharmacopée - Contribution aux études ethnobotaniques et floristiques en République Populaire du Congo. Agence de Coopération Culturelle et Technique, Paris, France. 606 pp.
• Agyeman, V.K., Ayarkwa, J., Owusu, F.W., Boachie-Dapaah, A.S.K., Addae-Mensah, A., Appiah, S.K., Oteng Amoako, A., Adam, A.R. & Pattie, D., 2003. Technological and investment profiles of some lesser used timber species in Ghana. Publication of International Tropical Timber Organization and Forestry Research Institute of Ghana, Accra, Ghana. 85 pp.
• ATIBT (Association Technique Internationale des Bois Tropicaux), 2004. Tropical wood and wooden product export statistics. ATIBT Newsletter 20: 29–47.
• ATIBT (Association Technique Internationale des Bois Tropicaux), 2005. Statistics. ATIBT Newsletter 22: 26–47.
• Ayarkwa, J., 2000. Cold and steam bending properties of some lesser-used species of Ghana. Ghana Journal of Forestry 9: 1–10.
• Bouquet, A., 1969. Féticheurs et médecines traditionnelles du Congo (Brazzaville). Mémoires ORSTOM No 36. Office de la Recherche Scientifique et Technique Outre-Mer. Paris, France. 282 pp.
• 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.
• 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.
• Diafouka, A., 1993. Utilisation populaire des plantes médicinales dans le district de Mbomo (Nord du Congo). Centre d'étude sur les ressources végétales (CERVE), Brazzaville, Congo. 6 pp. + 8 Tables.
• FORIG (Forestry Research Institute of Ghana), 1998. Proceedings of the international conference on value-added processing and utilization of lesser-used timber species. Smart Services Ltd., Kumasi, Ghana. 190 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.
• InsideWood, undated. [Internet] http://insidewood.lib.ncsu.edu/search/. Accessed May 2007.
• 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.
• Kouitcheu-Mabeku, L.B., Kouam, J., Penlap-Beng, V., Ngadjui, B.T., Fomum, Z.T. & Etoa, F.X., 2005. Evaluation of antimicrobial activity of the fruitrind of Picralima nitida (Apocynaceae) and the stem bark of Cylicodiscus gabunensis (Mimosaceae). West African Journal of Pharmacology and Drug Research 21(1): 6–12.
• Kouitcheu-Mabeku, L.B., Penlap-Beng, V., Kouam, J., Ngadjui, B.T., Fomum, Z.T. & Etoa, F.X., 2006. Evaluation of antidiarrhoeal activity of the stem bark of Cylicodiscus gabunensis (Mimosaceae). African Journal of Biotechnology 5(11): 1062–1066.
• 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.
• Owusu, F.W., 1998. Sanding properties of some seven Ghanaian lesser-used timber species. MSc degree thesis, Department of Wood Science and Technology, Institute of Renewable Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. University Press, Kumasi, Ghana. 163 pp.
• Phongphaew, P., 2003. The commercial woods of Africa. Linden Publishing, Fresno, California, United States. 206 pp.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
• Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 pp.
Sources of illustration
• Villiers, J.-F., 1989. Leguminosae - Mimosoideae. Flore du Gabon. Volume 31. Muséum National d’Histoire Naturelle, Paris, France. 185 pp.
• Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 pp.
Author(s)
J. Ayarkwa
Department of Building Technology, University P.O. Box 63, KNUST, Kumasi, Ghana
F.W. Owusu
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana


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
Photo editor
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Ayarkwa, J. & Owusu, F.W., 2008. Cylicodiscus gabunensis Harms. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.

















































Distribution Map wild


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



tree habit


base of bole


bole and crown


bole


slash


bark


fruit


opened fruit with seed


deckboard


flooring


wood


wood in transverse section


wood in tangential section


wood in radial section