Ongokea gore (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Fruit
Vegetable oil
Medicinal
Timber
Food security

Ongokea gore (Hua) Pierre

Protologue: Bull. Mens. Soc. Linn. Paris 2: 1314 (1897).

Family: Olacaceae

Synonyms

• Ongokea klaineana Pierre (1897),
• Ongokea kamerunensis Engl. (1909).

Vernacular names

• Angueuk, boleko, isano (En).
• Angueuk, boléko, ongokéa (Fr).
• Nsanu (Po).
• Kileku, ntuli, oleko (Sw).

Origin and geographic distribution

Ongokea gore occurs in dense evergreen and moist semi-deciduous forests from Sierra Leone to eastern DR Congo and south to Angola.

Uses

The wood of Ongokea gore, called ‘angueuk’ in trade, is used mostly locally in heavy construction, for railway sleepers and vehicle frames, in interior and exterior carpentry, for flooring, containers and boxes, turnery and veneer. It is well suited for interior joinery provided it is perfectly dry to avoid deformation. The seed oil, called ‘boleko oil’ or ‘isano oil’, is inedible but can be used as additive to linseed oil in the manufacture of paints, varnishes and linoleum and to oil for moulding cores in metal foundry. It can also be used to protect metal and wooden surfaces. Polymerization at moderately high temperatures yields a film with remarkable properties: strong, flexible and insoluble in acid and alkaline solvents. This makes it suitable for manufacturing brake pads and linings. In association with linseed oil the oil can be made into a standoil (a heat-polymerized oil, very thick and strongly adhesive, but slowly drying; used as a final coat in oil painting) of superior qualities. Boiling boleko oil with copal gives this resin a very high heat resistance. The oil can be used to make de-emulsifying products for the crude oil extraction industry and for the prevention of icing-up of airplane wings. It can also be vulcanized to yield highly resistant synthetic-rubber products. Ozonolytic cleavage can yield saturated double acids, which are used in the synthesis of polyamides. The use of fatty acids from boleko oil in the manufacturing of silicones and of isolating glue for lithium-based batteries has been patented. The oil is used traditionally to anoint the skin.

The pulp of the fruit is edible. The bark is laxative; in Congo fresh bark is rubbed on the breasts of lactating mothers to purge their babies; similarly, in Gabon a decoction of the bark is used as a wash for babies or they are given a pinch of pounded bark mixed with a little salt. The sap is used as styptic and the bark to treat splenomegaly in DR Congo. The seeds are used as bait for small rodents and the fruits as spinning tops for children.

Production and international trade

The wood of Ongokea gore is of little importance in international trade and is mostly included in statistics under ‘miscellaneous timbers’. Few accurate data are available: Equatorial Guinea exported 400 m³/year between 1963 and 1968, while Cameroon exported 500 m³/year in 1997 and 1998. In the Central African Republic the total extractible volume has been estimated at 3.7 million m³, of which 2.2 million m³ is quality class 1 and 2.

Boleko oil has been traded in small amounts. At the end of the 1950s less than 100 t/year were exported, although France and Belgium had high hopes to develop the use of the oil in the paint industry. Potential production at that time was estimated at 30,000 t/year for DR Congo alone. No information is available on the current production and trade of boleko oil.

Properties

The heartwood of Ongokea gore is pale yellow to pale brown and darkens on exposure to light. It is indistinctly demarcated from the 6–10 cm thick sapwood. The grain is straight, sometimes finely interlocked or wavy, texture fine and even. Quarter sawn surfaces are sometimes finely mottled or banded and slightly lustrous. The wood is heavy, with density at of 840–910 kg/m³ at 12% moisture content. The rates of shrinkage on drying are high, from green to oven dry 4.0% radial and 10.7% tangential. The wood should be dried slowly, and there is a high risk of distortion and a slight risk of checking. Logs should be quarter sawn before drying to avoid warping.

At 12% moisture content the modulus of rupture is 94–143 N/mm², modulus of elasticity 10,000–16,135 N/mm², compression parallel to grain 53–74 N/mm², shear 9.0–10.8 N/mm², and cleavage 19.8–33.6 N/mm.

Once dry the wood is easy to work, saw and plane with little blunting of tools. It is easy to finish, sand and polish. It can be painted, varnished, waxed and glued without difficulty. For nailing preboring is often required. It can be sliced into veneer, but requires much force.

The heartwood is durable; in a test in Japan it was little affected by decay fungi or termites and was resistant to marine borers and in a test in Ghana it was little affected in a 3-year wood graveyard test. The sapwood is sensitive to blue-stain and to dry-wood borers. The heartwood is extremely resistant to impregnation, whereas the sapwood moderately resistant.

The dry seed contains about 63% oil. The seed oil differs from other vegetable oils in its fatty acid composition. Boleko oil has a high iodine number, but it does not dry when exposed in a thin film such as linseed oil or tung oil. When heated to 250°C a strongly exothermic spontaneous polymerization reaction starts, which may lead to a further increase in temperature to more than 400°C and to an explosion. Diacetylenic fatty acids and hydroxy-diacetylenic fatty acids characterize the oil; it consists mainly of: isanic acid and bolekic acid (together 30–50%) and of isanolic acid (15–35%). It further contains saturated and unsaturated fatty acids of which linoleic acid is the most important one. Isanic acid is an unbranched C₁₈-fatty acid with a single ethylene bond and 2 conjugated acetylene bonds; its formula is 17-octadecene-9,11-diynoic acid. Bolekic acid is 13-octadecene-9,11-diynoic acid, isanolic acid 17-octadecene-8-hydroxy-9,11-diynoic acid. The unsaponifiable matter of the oil contains a crystalline dialcohol with molecular formula C₂₈H₄₄O₂.

The pulp of the fresh fruit contains 67% moisture; its smell is reminiscent of apple, it is sweet but slightly astringent. The root and stem bark of Ongokea gore contain cyclohexanoid protaflavanones named ongokeins; they are related to sakuranetin and are characterized by a non-aromatic C₆-ring moiety that is otherwise only known from certain ferns.

Description

Medium-sized to large, glabrous tree up to 40 m tall; bole straight and cylindrical, unbranched for up to 20 m, 100(–150) cm in diameter, without buttresses but sometimes with heavy root swellings; bark grey to dark brown or black, 1–2 cm thick, finely fissured and peeling off in fine irregular scales; crown pyramidal, rather open, with few heavy branches; leaf-bearing branches laterally compressed. Leaves alternate, simple and entire, without stipules; petiole thin, 0.5–1 cm long, grooved above, decurrent into 2 fine ridges along the branch; blade elliptical, 4–12 cm × 2–5 cm, base rounded to cuneate, apex shortly acuminate, margins retrorse especially near the base, lateral veins 6–10 at each side of the midrib, joining at some distance from the margin. Inflorescence an axillary panicle, up to 15 cm long, consisting of densely flowered, umbel-shaped cymes. Flowers bisexual or functionally unisexual, regular, 4-merous, greenish; pedicel filiform, c. 6 mm long; calyx shallowly cup-shaped, c. 1 mm in diameter; petals strap-shaped, 3–4 mm long, recurved; disk 4 lobed; stamens united into a tube c. 3 mm long; ovary superior, sessile, 1-celled, style hardly exserted from the staminal tube. Fruit a globose drupe, 2–4 cm in diameter, enclosed by the enlarged calyx except for apical part, slightly acuminate, 1-seeded. Seed globose, c. 1.5 cm in diameter. Seedling with epigeal germination; hypocotyl very short, epicotyl c. 18 cm long; first pair of leaves opposite.

Other botanical information

Ongokea comprises a single species. It is closely related to Aptandra a genus with about 4 species in tropical America and one species in tropical Africa, Aptandra zenkeri Engl., which differs from Ongokea gore in its raceme-like inflorescences and large, collar-shaped, pinkish calyx surrounding the fruit.

Growth and development

In Côte d’Ivoire Ongokea gore flowers from January to June and fruits from May to July; in DR Congo fruiting is abundant in September, in Gabon in December and January. The fruits are eaten by many animals and the seeds are dispersed e.g. by monkeys.

Ecology

Ongokea gore is found scattered in dense evergreen forest and in moist semi-deciduous forest. It occurs on dry ground and in periodically inundated localities. In Gabon it often occurs in forest dominated by Sacoglottis gabonensis (Baill.) Urb. and Aucoumea klaineana Pierre.

Propagation and planting

Germination is slow and may take several months and even more than one year. Because of its slow and irregular germination, Ongokea gore is not grown in nurseries.

Management

Large trees of Ongokea gore occur scattered in the forest. In Liberia 1 tree with a bole diameter over 60 cm has been reported per 43 ha for evergreen forest, and 1 tree per 7.5 ha for moist semi-deciduous forest.

Harvesting

Fruits of Ongokea gore are collected from the wild and mostly the pulp is allowed to rot away before the fruit stones are collected from the soil.

Handling after harvest

Fresh logs sink in water and cannot be transported by river. Depulping of fruits can be done by passing the fruits between rubber rollers and washing them with cold water. Boleko oil is produced by hydraulic pressing, but this is hampered by the high viscosity of the oil. During pressing the temperature can rise to 80°C which can alter the properties of the oil. The press cake contains considerable amounts of polymerized oil. The cake is unsuitable as cattle feed, but can be used as manure. The oil can also be extracted by solvents after the kernels have been ground and subjected to treatment with cold methanol.

Genetic resources

Ongokea gore is widespread and does not seem to be in danger of genetic erosion. No germplasm collections are known to exist.

Prospects

Ongokea gore is likely to remain important in its region of origin. There are no indications that it will become a commodity in international trade, but its volume in miscellaneous timber lots is likely to increase. Demand for the oil is likely to remain low except if local paint industries develop or if new applications for its unique fatty acids are found.

Major references

• Anonymous, 1957. Angueuk. Bois et Forêts des Tropiques 54: 23–26.

• 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.

• Chudnoff, M., 1980. Tropical timbers of the world. USDA Forest Service, Agricultural Handbook No 607, Washington D.C., United States. 826 pp.

• CIRAD Forestry Department, 2003. Angueuk. [Internet] Tropix 5.0. http://tropix.cirad.fr/ afr/angueuk.pdf. September 2005.

• CTFT (Centre Technique Forestier Tropical), undated. Résultats des observations et des essais effectués au CTFT sur angueuk - Ongokea gore. Information technique 140. Centre Technique Forestier Tropical, Nogent sur Marne, France. 5 pp.

• Miller, R.W., Weisleder, D., Kleiman, R., Plattner, R.D. & Smith Jr, C.R., 1977. Oxygenated fatty acids of isano oil. Phytochemistry 16: 947–951.

• Normand, D., 1950. Atlas des bois de la Côte d’Ivoire. Tome 1. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 148 pp.

• Pouliquen, F., 1959. Contribution à l’étude de l’huile d’Ongokéa. Oléagineux 14: 381–385, 453–459, 541–547.

• Vieux, A.S. & Taratibu, T., 1968. L’huile de boléko, essai de fractionnement sélectif par extraction liquide-liquide. Oléagineux 23(5): 325–329.

• Voorhoeve, A.G., 1979. Liberian high forest trees. A systematic botanical study of the 75 most important or frequent high forest trees, with reference to numerous related species. Agricultural Research Reports 652, 2nd Impression. Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands. 416 pp.

Other references

• Burkill, H.M., 1997. The useful plants of West Tropical Africa. 2nd Edition. Volume 4, Families M–R. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 969 pp.

• De Borger, R., 1960. Notes sur la valeur nutritive des amandes d’Ongokea gore et de Parinari pumila. Revue des Fermentations et des Industries Alimentaires 15: 167–170.

• De Vries, E., 1956. L’huile de boléko. Direction de l’Agriculture, des Forêts et de l’Elevage, Brussels, Belgium. 166 pp.

• De Vries, E., 1957. L’huile de boléko. Oléagineux 12(7): 427–431.

• Heckel, E., 1902. Les graines grasses nouvelles ou peu connues des colonies françaises. Challamel, Paris, France. 185 pp.

• Jerz, G., Waibel, R. & Achenbach, H., 2005. Cyclohexanoid protoflavanones from the stem-bark and roots of Ongokea gore. Phytochemistry 66: 1698–1706.

• 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.

• Libouga, D.G., Womeni, H.M. & Bitjoka, L., 2002. Extrait des ecorces de l’Ongokea gore: protéolysé et conservation. Journal of the Cameroon Academy of Sciences 2(2): 96–108.

• Magliocca, F., 1998. Bilan provisoire de la fréquentation par les grands mammifères de la clairière Maya Nord août & septembre 1998. Ecofac-Composante Congo. 13 pp.

• Mangala, M., 1999. Evaluation des ressources forestières ligneuses dans la République Centrafricaine. [Internet] http://www.fao.org/ documents/show_cdr.asp?url_file=/DOCREP/004/ X6805F/X6805F03.htm. May 2005.

• 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.

• Pauwels, L., 1993. Nzayilu N’ti: guide des arbres et arbustes de la région de Kinshasa Brazzaville. Scripta Botanica Belgica. Volume 4. Jardin botanique national de Belgique, Meise, Belgium. 495 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.

• Saunders, R.G. & Hall, G.S., 1968. Marine borer resistance of timbers. Research Report of the Timber Research and Development Association, High Wycombe, United Kingdom. 26 pp.

• Tsunoda, K., 1990. The natural resistance of tropical woods against biodeterioration. Wood Research 77: 18–34.

• Villiers, J.-F., 1973. Olacacées. Flore du Gabon. Volume 20. Muséum National d’Histoire Naturelle, Paris, France. pp. 101–162.

• von Mikusch, J.D., 1963. Einige Besonderheiten des Isanoöls. Farbe und Lack 69: 663–671.

• von Mikusch, J.D., 1964. Die trocknenden Öle: das Isanoöl. Farbe und Lack 70: 17–28; 101–110.

• 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

• Pauwels, L., 1993. Nzayilu N’ti: guide des arbres et arbustes de la région de Kinshasa Brazzaville. Scripta Botanica Belgica. Volume 4. Jardin botanique national de Belgique, Meise, Belgium. 495 pp.

• Voorhoeve, A.G., 1979. Liberian high forest trees. A systematic botanical study of the 75 most important or frequent high forest trees, with reference to numerous related species. Agricultural Research Reports 652, 2nd Impression. Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands. 416 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.

Author(s)

• 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

Correct citation of this article

Louppe, D., 2007. Ongokea gore (Hua) Pierre. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 17 December 2024.

• See the Prota4U database.