Antrocaryon micraster A.Chev.

Family

Anacardiaceae

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Chromosome number

2n = 24

Synonyms

Vernacular names

Origin and geographic distribution

Antrocaryon micraster is widespread, occurring from Guinea and Sierra Leone east to Uganda, and south to Gabon.

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Uses

The wood, traded from Côte d’Ivoire as ‘akoua’, from Ghana as ‘aprokuma’ and on the international timber market as ‘onzabili’, is locally used, mainly for general carpentry, planks in house building, and furniture. It is suitable for joinery, interior trim, beams, frames, boxes, crates, light pallets, coffins, veneer and plywood. It is also used as firewood and for charcoal production.
The flesh of the fruits is locally eaten, and sometimes it is fermented to prepare an alcoholic drink. The seeds, which are rich in oil, are also edible and consumed locally. In traditional medicine the fruits are taken to relieve pains in chest and stomach, and to treat toothache and cough; the fruit juice is applied externally against lice. The bark is used as an enema to treat impotence, and in mixtures to treat threatened abortion.

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Production and international trade

The wood of Antrocaryon micraster is mainly used locally and occasionally traded on the international market. Information on production and trade statistics indicates that it is only occasionally exported. In 1996 plywood was exported from Ghana at an average price of US$ 400/m³.

Properties

The heartwood is greyish pink, becoming reddish brown upon exposure, and not distinctly demarcated from the greenish to yellowish white sapwood. The grain is straight, texture medium. The wood is lustrous, odourless and tasteless when dry.
The wood is medium-weight, with a density of about 520 kg/m³ at 12% moisture content. It air dries rapidly and well with only slight distortion. The rates of shrinkage are rather high, from green to oven dry 4.8–6.0% radial and 7.4–8.0% tangential. Once dry, the wood is moderately stable in service. At 12% moisture content, the modulus of rupture is 71–116 N/mm², modulus of elasticity 10,580 N/mm², compression parallel to grain 31–44 N/mm², shear 8 N/mm², cleavage 13 N/mm and Chalais-Meudon side hardness 1.8.
The wood works and saws well with both hand and machine tools, with only slight blunting effect on cutting tools. The nailing and screwing properties are satisfactory. The wood has good gluing characteristics and takes a fine polish. It has a low durability and is liable to fungal, Lyctus and termite attacks. The wood is easily treated with preservatives. It has high contents of cellulose, pentosan and starch, but has a low lignin content.
The composition of the seeds per 100 g is: water 3.7 g, protein 10.8 g, fat 70 g, carbohydrate 14.6 g, fibre 2.5 g, ash 0.9 g, Ca 67 mg and P 558 mg. The seeds contain about 70% edible oil. The main components of the oil are linoleic acid (about 40%), oleic acid (about 30%) and stearic acid (about 18%). An exceptionally high content of ascorbic acid (327 mg per 100 g edible portion) has been reported for the seeds.

Adulterations and substitutes

The wood of Antrocaryon spp. resembles that of okoumé (Aucoumea klaineana Pierre) and ilomba (Pycnanthus angolensis (Welw.) Warb.), which are both commonly used for veneer and plywood.

Description

Deciduous, dioecious, medium-sized to large tree up to 45(–50) m tall; bole branchless for up to 30 m, straight and cylindrical but often twisted in upper part, up to 130 cm in diameter, usually slightly thickened at base or with small buttresses; bark surface grey, fissured and scaly, with lenticels, inner bark thick, fibrous, reddish with white streaks, with turpentine smell and exuding a translucent resin; crown spreading; twigs thick, slightly angular. Leaves arranged spirally, clustered near ends of branches, imparipinnately compound with (4–)5–10 pairs of leaflets; stipules absent; petiole and rachis together 20–50 cm long, hairy; petiolules 1–5 mm long, grooved; leaflets opposite, narrowly ovate to oblong-lanceolate or oblong-elliptical, 5–11 cm × 1.5–4 cm, rounded and asymmetrical at base, acuminate at apex, papery, short-hairy on both surfaces, pinnately veined with 20–30 pairs of parallel lateral veins. Inflorescence an axillary lax panicle up to 25 cm long with long branches, hairy. Flowers unisexual, regular, 5-merous; pedicel short, jointed; calyx with lobes c. 1 mm long, slightly fused at base, short-hairy; petals free, oblong-ovate, 1.5–2 mm long, reflexed, short-hairy, yellowish white or greenish white; stamens 10, c. 1.5 mm long; disk thick and slightly lobed; ovary superior, depressed-globose, 1–2 mm in diameter, glabrous, 5-celled, styles 5, short; male flowers with rudimentary ovary, female flowers slightly larger and with rudimentary stamens. Fruit a depressed-globose drupe c. 3.5 cm × 5 cm, yellow when ripe; stone depressed-globose, slightly 5-lobed, c. 2.5 cm × 4 cm, with 5 apical cavities, 3–4-seeded. Seeds flattened and curved. Seedling with epigeal germination; hypocotyl 7–12 cm long, glabrous, pinkish, epicotyl 10–20 cm long, hairy, whitish; cotyledons linear-oblong, thick and fleshy; first 2 leaves opposite, imparipinnately compound.

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Other botanical information

Antrocaryon comprises 3 species and occurs from Sierra Leone east to Uganda.
Antrocaryon nannanii De Wild. closely resembles Antrocaryon micraster, apparently differing in its obovoid to globose fruit stone. It occurs in eastern Gabon, Congo, DR Congo and Cabinda (Angola). The wood, with a density of 510–695 kg/m³ at 12% moisture content, is also similar and used for joinery, furniture and veneer. It is suitable for fibreboard and particle board, and for paper production. The oily seeds are edible. Leaves and bark are used to treat complaints of liver and digestive organs, and against cough. Fruit stones are sold in local markets for medicinal and magical applications.

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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; 27: intervessel pits large (≥ 10 μm); 31: vessel-ray pits with much reduced borders to apparently simple: pits rounded or angular; 42: mean tangential diameter of vessel lumina 100–200 μm; 43: mean tangential diameter of vessel lumina ≥ 200 μm; 47: 5–20 vessels per square millimetre. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 65: septate fibres present; (66: non-septate fibres present); 68: fibres very thin-walled. Axial parenchyma: 75: axial parenchyma absent or extremely rare; 78: axial parenchyma scanty paratracheal; (92: four (3–4) cells per parenchyma strand); 93: eight (5–8) cells per parenchyma strand; 94: over eight cells per parenchyma strand. Rays: 97: ray width 1–3 cells; 106: body ray cells procumbent with one row of upright and/or square marginal cells; 107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells; 115: 4–12 rays per mm. Secretory elements and cambial variants: (130: radial canals). Mineral inclusions: (136: prismatic crystals present); (137: prismatic crystals in upright and/or square ray cells).
(N.P. Mollel, H. Beeckman & P. Baas)

Growth and development

Antrocaryon micraster is a light demanding species with rapid seedling growth. Seedlings can reach a height of 30 cm in 6 weeks and 1.5 m in one year. The tree is often deciduous from the end of November to the end of January, but flushes of new leaves appear gradually and continuously until March. Young leaves are reddish. Flowering of trees has been recorded from November to July, but in Côte d’Ivoire the main flowering period is March–April. In Ghana fruiting is usually from April to June, in Nigeria from September to October, but in Côte d’Ivoire it has been reported that ripe fruits can be found in both periods. Generally the tree produces fruits profusely and natural regeneration occurs near the mother tree. In Guinea fruits are reported to be abundant once every 3 years. The fruits are eaten by mammals such as monkeys and elephants, which may serve as dispersers of the stones. Chimpanzees may use stones to break the fruit stones, after which they eat the seeds.

Ecology

Antrocaryon micraster occurs mostly in semi-deciduous forest. In Uganda it is found in rainforest at 1000–1500 m altitude. It is susceptible to forest fires.

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Propagation and planting

Antrocaryon micraster regenerates well in forest clearings and canopy gaps. However, seedlings do not compete well with weeds. There are about 45 stones per kg. Seeds are very difficult to extract from the stones. Seeds may start germinating 2 weeks after sowing, but the start of germination of stones can take as long as 3 years. The germination rate is often low; in Côte d’Ivoire it has been reported as 20–30%, but also as 50–80%. More than one seedling per stone is common. Propagation can be done with stumped saplings. Wildlings have been successfully transplanted to the nursery. They can reach about 40 cm tall after 3–4 months, and can be transplanted to the field in full sun.

Management

In general, Antrocaryon micraster occurs scattered in the forest. In forests in Ghana, an average stocking of 0.5 m³/ha of boles above 30 cm diameter was reported in 2001. The standing stock was estimated at 402,800 m³, out of which 342,000 m³ were in the exploitable diameter classes above 50 cm; the annual allowable cut was estimated at 8500 m³.

Harvesting

The minimum bole diameter for harvesting Antrocaryon micraster is 50 cm in Ghana.

Yield

A bole without serious defects may yield 12–18 m³ of usable wood.

Handling after harvest

Freshly harvested boles sink in water and thus cannot be transported by river. Logs should be removed from the forest immediately after felling, or treated with preservatives, because they are susceptible to blue stain attack.

Genetic resources and breeding

Although Antrocaryon micraster is locally not uncommon and its exploitation seems to be moderate, it is included as vulnerable in the IUCN Red List of threatened species. The status of the species should be reviewed.

Prospects

Antrocaryon micraster is currently not exploited on a large scale, but it has potential commercial value due to its relatively large bole size. More research is needed on appropriate management systems to ensure sustainable exploitation from the natural forest and to find out its potential as a plantation species. A biosystematic study is needed to confirm the claimed differences between Antrocaryon micraster and Antrocaryon nannanii.

Major references

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• Hansen, C.P. & Treue, T., 2008. Assessing illegal logging in Ghana. International Forestry Review 10(4): 573–590.
• 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.
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• Kokwaro, J.O., 1986. Anacardiaceae. In: Polhill, R.M. (Editor), 1986. Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 59 pp.
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Other references

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Afriref references

Sources of illustration

• 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.
• Kokwaro, J.O., 1986. Anacardiaceae. In: Polhill, R.M. (Editor), 1986. Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 59 pp.

Author(s)

•	J. Ayarkwa Department of Building Technology, University P.O. Box 63, KNUST, Kumasi, Ghana

Editors

•	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

Ayarkwa, J., 2011. Antrocaryon micraster A.Chev. & Guill. [Internet] Record from PROTA4U. 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. <http://www.prota4u.org/search.asp>. Accessed .

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