Strombosia pustulata (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

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

Strombosia pustulata Oliv.

Protologue: Hooker’s Icon. pl. 23: t. 2299 (1894).

Family: Olacaceae

Synonyms

Strombosia glaucescens Engl. (1909).

Origin and geographic distribution

Strombosia pustulata occurs from Guinea Bissau east to the Central African Republic, and southwards to DR Congo and Cabinda (Angola).

Uses

The wood, known as ‘afina’, ‘afena’ or ‘poé’, is locally used for heavy construction including hydraulic work, poles, railway sleepers, utensils, drainage boards and tool handles. It is suitable for flooring, joinery, mine props, ship building, vehicle bodies, toys, novelties, agricultural implements, carvings, turnery and sliced veneer. It is also used as firewood and for charcoal production. The wood pulp has been tried in paper making, but it was found unsuitable because the pulp yield was low.

The plant has various medicinal uses throughout its distribution area. In West Africa the pulped bark is rubbed on the skin to treat skin complaints, wounds and sores. In Côte d’Ivoire the leaf sap is taken to treat hiccups. Different parts of the plant are used in treating cough, abscesses and furuncles. In Nigeria the seed oil is used as laxative and as lubricant for massaging. In Cameroon powdered bark, together with seeds of Aframomum melegueta K.Schum., is externally applied to aching muscles and kidneys. In Gabon bark decoctions are taken to treat dysentery, stomach-ache, backache and pain in the side. In Ghana the seed oil is used as ointment and in soap making.

Production and international trade

The wood of Strombosia pustulata is mainly used locally and rarely traded on the international market and then often sold in mixed consignments with other Strombosia spp.

Properties

The heartwood is pale brown with purplish streaks, and more or less distinctly demarcated from the yellowish to pale brown, wide sapwood. The grain is fairly straight, sometimes wavy, texture fine. The wood is lustrous, slightly gummy and rather oily to the touch, with an unpleasant odour when freshly cut.

The wood is heavy, with a density of 850–1020 kg/m³ at 12% moisture content, and hard. Air drying can be problematic, with a high risk of distortion and splitting. Slow drying is recommended. The shrinkage rates are high, from green to oven dry 7.4–8.6% radial and 7.9–11.4% tangential. Once dry, the wood is unstable in service. At 12% moisture content, the modulus of rupture is (115–)170–243 N/mm², modulus of elasticity 16,370–20,190 N/mm², compression parallel to grain 58–90 N/mm², cleavage 18–38 N/mm and Chalais-Meudon side hardness 5.3–7.9(–12.8).

Considering the high density, the wood saws and works comparatively easily with both hand and machine tools. It takes a smooth finish and polishes well. Splitting is common in nailing, and pre-boring is recommended. The wood glues well. It has a high natural durability with an expected service life of up to 50 years. The heartwood is very resistant to fungal and termite attacks, but the sapwood is moderately resistant and susceptible to Lyctus borers. The heartwood is very resistant to preservative treatment, the sapwood is permeable.

The wood contains 39–42.5% cellulose, 31–38% lignin, 12–16% pentosan, 0.3–1.9% ash and up to 0.02% silica. The solubility is 0.8–3.3% in alcohol-benzene, 0.4–4.8% in hot water and 9.1–18.6% in a 1% NaOH solution.

Seed samples from Côte d’Ivoire yielded 15–18% of a reddish brown oil with a disagreeable smell, whereas samples from Nigeria yielded 2–3% of a golden-yellow oil.

Description

Evergreen medium-sized tree up to 25(–35) m tall; bole cylindrical, usually straight, up to 60(–100) cm in diameter, slightly fluted at base or with low buttresses; bark surface grey-black, with numerous small corky lenticels, becoming scaly with an irregular pattern of olive-green and whitish patches, inner bark thin, hard, granular, pale yellow to pale orange or brown with narrow white streaks; crown dense, small and rounded; twigs more or less angled, glabrous. Leaves alternate, simple and entire; stipules absent; petiole 0.5–1(–2.5) cm long, grooved above; blade ovate to elliptical or oblong-elliptical, 4–11(–25) cm × 2–7(–18) cm, base cuneate to rounded, often slightly asymmetrical, apex acute to short-acuminate, thick-papery, glabrous, more or less pustulate, pinnately veined with 4–7(–10) pairs of lateral veins. Inflorescence a compact axillary fascicle, usually few-flowered. Flowers bisexual, regular, 5-merous; pedicel 1–3 mm long; calyx lobes almost circular, c. 1 mm long, hairy at margins; petals free, linear-oblong, (2–)3–5 mm long, upper inner half densely short-hairy, outside glabrous, pale green, whitish or yellowish; stamens 3–4 mm long, filaments fused for 1–3 mm with petals; ovary inferior or semi-inferior, c. 1 mm in diameter, 1-celled but at base 5-celled, upper part surrounded by disk, style 1–3 mm long, stigma (3–)5-lobed. Fruit a broadly ellipsoid or globose drupe 1–3 cm in diameter, enclosed by fleshy calyx, blackish purple when ripe, with depression at apex, stone 1-seeded. Seeds ellipsoid, wrinkled, with much waxy endosperm. Seedling with epigeal germination; hypocotyl 8–15 cm long, epicotyl 1–3 cm long; cotyledons nearly orbicular, 3–6 cm in diameter, 3–5-veined from the base; first leaves alternate.

Other botanical information

Strombosia comprises about 10 species, 7 of which occur in tropical Africa and 3 in tropical Asia. It has been classified in Olacaceae, but recent molecular studies showed that it is better placed in a separate family Strombosiaceae, together with 5 other genera including Strombosiopsis. The wood of some other Strombosia spp. is used for similar purposes as that of Strombosia pustulata.

Strombosia grandifolia

Strombosia grandifolia Hook.f. is a shrub or small to medium-sized tree up to 25 m tall with bole up to 60 cm in diameter, occurring from Nigeria east to southern Sudan and south to Cabinda (Angola). Its reddish brown, heavy wood, with a density of (680–)950–1010(–1280) kg/m³ at 12% moisture content, is used for construction, dug-out canoes, railway sleepers, tool handles and carvings; it is fairly easy to saw and has good durability. The bark yields a dye which is used in DR Congo to blacken pottery. In the Central African Republic pulverized bark wrapped in a large leaf is warmed over a fire and applied to oedema. In Gabon the bark is used to treat chest complaints, post-partum pain and kidney pain. In DR Congo bark decoctions are taken to treat tuberculosis, as an emetic. In Gabon the seed is sometimes eaten after thorough drying, cooking and washing to remove toxicity and bitterness.

Strombosia zenkeri

Although Strombosia zenkeri Engl. is a small tree up to 15 m tall, its wood is probably used for similar purposes as that of Strombosia pustulata. It occurs in south-eastern Nigeria, Cameroon, Gabon and Congo. It has been reported that bark and leaf sap are used in traditional medicine in Congo as a substitute of Strombosiopsis tetrandra Engl.

Anatomy

Wood-anatomical description (IAWA hardwood codes):

• Growth rings: 2: growth ring boundaries indistinct or absent.
• Vessels: 5: wood diffuse-porous; 14: scalariform perforation plates; 16: scalariform perforation plates with 10–20 bars; 17: scalariform perforation plates with 20–40 bars; 20: intervessel pits scalariform; 21: intervessel pits opposite; 27: intervessel pits large (≥ 10 μm); 32: vessel-ray pits with much reduced borders to apparently simple: pits horizontal (scalariform, gash-like) to vertical (palisade); 41: mean tangential diameter of vessel lumina 50–100 μm; 48: 20–40 vessels per square millimetre; (49: 40–100 vessels per square millimetre); 56: tyloses common; 57: tyloses sclerotic.
• Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 70: fibres very thick-walled.
• Axial parenchyma: 76: axial parenchyma diffuse; 77: axial parenchyma diffuse-in-aggregates; (78: axial parenchyma scanty paratracheal); 93: eight (5–8) cells per parenchyma strand; 94: over eight cells per parenchyma strand.
• Rays: 97: ray width 1–3 cells; 107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells; 108: body ray cells procumbent with over 4 rows of upright and/or square marginal cells; 115: 4–12 rays per mm; 116: ≥ 12 rays per mm.
• Mineral inclusions: 136: prismatic crystals present; 137: prismatic crystals in upright and/or square ray cells; 138: prismatic crystals in procumbent ray cells; 140: prismatic crystals in chambered upright and/or square ray cells; 141: prismatic crystals in non-chambered axial parenchyma cells; (142: prismatic crystals in chambered axial parenchyma cells); 157: crystals in tyloses.

(E. Uetimane, P. Baas & H. Beeckman)

Growth and development

Strombosia pustulata is considered to be slow growing. In silvicultural trials in Ghana, seedlings reached 15 cm tall after 1 year and saplings 1 m tall when 4 years old. Strombosia pustulata is considered a shade bearer, but seedlings and saplings grow well in small canopy gaps. In Côte d’Ivoire trees flower from June to September, in Nigeria from October to December, and ripe fruits are found about 3 months after flowering. The fruits are relished by birds such as hornbills and also by elephants, serving thus as important seed dispersers.

Ecology

Strombosia pustulata occurs in evergreen forest and moist semi-deciduous forest, at low altitudes. It is most common in undisturbed forest. It is in general non-selective of soil conditions but prefers free draining soils.

Propagation and planting

There are about 800 fruit stones per kg. Germination is irregular, varying from 2 weeks to 10 weeks after sowing, but the germination rate is generally high, up to 90%. Propagation by wildlings is sometimes practised; these may be very abundant near the mother tree.

Management

Strombosia pustulata is often common, usually forming part of the dominant species in the middle storey of the forest. In evergreen forest in Ghana, an average density of 60 boles/ha has been reported, but most of the boles had a diameter of less than 30 cm.

Genetic resources

Strombosia pustulata is widespread and locally common, sometimes even dominant, within its geographical range, and it is not threatened at present. However, its preference for undisturbed forest may make it liable to genetic erosion in forest that is subject to serious damage by logging practices.

Prospects

Strombosia pustulata is a useful local source of wood and traditional medicine. It does not seem to be promising for more commercial exploitation because of its vulnerability to logging practices in the forest and slow growth. The chemical and pharmaceutical properties of the bark and seed oil deserve further investigation.

Major references

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• 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.

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• 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.

• 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.

• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.

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Other references

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• de Koning, J., 1983. La forêt de Banco. Part 2: La Flore. Mededelingen Landbouwhogeschool Wageningen 83–1. Wageningen, Netherlands. 921 pp.

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Sources of illustration

• Voorhoeve, A.G., 1965. Liberian high forest trees. A systematic botanical study of the 75 most important or frequent high forest trees, with reference to numerous related species. Pudoc, 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)

• A.A. Oteng-Amoako, Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article

Oteng-Amoako, A.A., 2012. Strombosia pustulata Oliv. In: Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 5 April 2025.

• See the Prota4U database.