Guarea thompsonii (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Medicinal
Timber
Fuel
Ornamental
Conservation status

distribution in Africa (wild)

1, base of bole; 2, leaf; 3, leaflet; 4, fruit; 5, fruit in cross section. Redrawn and adapted by Iskak Syamsudin

various parts of the tree (W.D. Hawthorne)

wood in transverse section

wood in tangential section

wood in radial section

Guarea thompsonii Sprague & Hutch.

Protologue: Bull. Misc. Inform. Kew 1906: 245 (1906).

Family: Meliaceae

Chromosome number: 2n = 72

Vernacular names

• Dark bosse, sweet cedar, black guarea (En).
• Bossé foncé, guarea noir (Fr).

Origin and geographic distribution

Guarea thompsonii occurs from Liberia to Gabon and DR Congo.

Uses

The wood is valued for house building, flooring, joinery, interior trim, panelling, doors, ship building, vehicle bodies, furniture, cabinet work, veneer and plywood. It is suitable for toys, novelties, boxes, crates, carving and turnery. Traditionally, the wood is used for dugout canoes.

The bark is used in traditional medicine. In Côte d’Ivoire bark decoctions are applied as an enema to treat kidney pain, bleeding after childbirth, rheumatism and leprosy. A bark maceration is taken as a strong purgative.

Production and international trade

The wood of Guarea thompsonii, Guarea cedrata (A.Chev.) Pellegr. and Guarea laurentii De Wild. is all traded as ‘bosse’. Congo exported 11,000 m³ of Guarea logs in 2003, at an average price of US$ 174/m³, 15,000 m³ in 2004, at an average price of US$ 177/m³, and 25,000 m³ in 2005, at an average price of US$ 172/m³. Exports of Guarea sawnwood from Congo were 4000 m³ in 2004, at an average price of US$ 333/m³, and 9000 m³ in 2005, at an average price of US$ 304/m³. Small amounts of veneer were exported from Congo in 2003 and 2004, at an average price of US$ 331/m³ and 363 US$/m³, respectively. Cameroon exported 12,250 m³ and 11,700 m³ of Guarea logs in 1997 and 1998, respectively, and exports of sawn ‘bosse’ were 4150 m³ in 2003, 3300 m³ in 2004, and 3000 m³ in 2006. The Central African Republic exported 3,200 m³ of logs in 1999, and 2300 m³ in 2006. Ghana exported 2450 m³ of Guarea logs in 1994, at an average price of US$ 221/m³, and 3710 m³ of sawn wood, at an average price of US$ 424/m³. Guarea has some importance as export timber in Gabon, with in 2001–2005 an annual export volume of about 5000 m³ of logs for all Guarea species together. The share of Guarea thompsonii in these statistics is obscure.

Properties

The heartwood is pinkish brown when freshly cut, darkening to reddish brown upon exposure. It is usually distinctly demarcated from the paler sapwood. The grain is usually straight, sometimes interlocked, texture fine. The wood has a slight cedar-like smell when fresh. It may have some gummy exudate.

The wood is medium-weight, with a density of 620–740 kg/m³ at 12% moisture content. It generally air dries fairly easily with little degrade, but has some tendency to checking during kiln drying. The rates of shrinkage are moderately high, from green to oven dry 5.2–5.5% radial and 6.5–7.0% tangential. Once dry, the wood is fairly stable in service.

At 12% moisture content, the modulus of rupture is 101–171 N/mm², modulus of elasticity 10,800–14,500 N/mm², compression parallel to grain 58–69 N/mm², shear 12–14 N/mm², cleavage 15–18 N/mm, Janka side hardness 4890 N and Janka end hardness 6090 N.

The wood is usually fairly easy to saw and work; it contains less silica than the wood of Guarea cedrata, but is slightly more dense. It can be finished to a smooth surface, but there may be a slight tendency to pick up during planing of quarter-sawn material and some gum may appear at the surfaces. A cutting angle of 20° is recommended when interlocked grain is present. The wood holds nails and screws well, but may split upon nailing and pre-boring is recommended. It glues satisfactorily and takes paints, varnishes and stains well, but filling is recommended. The bending properties are usually moderate. Good-quality veneer can be produced by slicing. The wood dust may cause irritation to the skin and mucous membranes.

The wood is moderately durable and only occasionally attacked by termites and pinhole borers, but it is slightly more susceptible to attacks of powder-post beetles. The heartwood is strongly resistant to impregnation, the sapwood permeable to moderately resistant.

Adulterations and substitutes

The wood of Guarea cedrata (A.Chev.) Pellegr. is sometimes mixed with that of Guarea thompsonii, but is usually slightly lighter in weight and colour. The wood resembles that of Khaya spp., and is also close to that of Entandrophragma spp.

Description

• Evergreen, dioecious, medium-sized to fairly large tree up to 35(–55) m tall; bole branchless for up to 20 m, usually straight, often fluted, up to 150 cm in diameter, sometimes with short, blunt buttresses at base; bark surface greyish to brown, smooth to warty but exfoliating in rectangular scales leaving concentric rings of markings (mussel shell pattern), inner bark yellowish, granular, with or without cedar-like smell, exuding latex; crown rounded, dense; twigs short-hairy but glabrescent.
• Leaves arranged spirally, paripinnately or imparipinnately compound with (3–)4–8 pairs of leaflets; stipules absent; petiole 6–14 cm long, slightly winged at margins and slightly grooved, rachis 8–30 cm long; petiolules 5–7 mm long, but in terminal leaflet up to 3.5 cm; leaflets opposite or nearly so, oblong-elliptical to obovate-elliptical, 12–34 cm × 4–11 cm, cuneate and slightly asymmetrical at base, obtuse or shortly acuminate at apex, margins entire to wavy, thickly papery or thinly leathery, glabrous, pinnately veined with 9–16 pairs of lateral veins, smallest veins not conspicuous.
• Inflorescence an axillary panicle or raceme up to 30 cm long, sparsely hairy or glabrous.
• Flowers unisexual, male and female flowers very similar in appearance, regular, 4–5-merous, pale yellow, fragrant; pedicel 2–5 mm long; calyx cup-shaped, 1–2 mm long, entire or with very short lobes; petals free, elliptical-oblong to obovate-elliptical, 8–15 mm × 3–6 mm; stamens fused into an urn-shaped tube 8–10 mm long, with 8–10 included anthers near apex, alternating with rounded lobes; ovary superior, globose to flask-shaped, 6–7 mm long, 4-celled, style c. 4 mm long, thick, stigma disk-shaped; male flowers with rudimentary ovary, female flowers with smaller, non-dehiscing anthers.
• Fruit a nearly globose capsule 3–4 cm in diameter, reddish purple, glabrous, rough, dehiscing by 3–4 valves, 1–2(–4)-seeded.
• Seeds kidney-shaped to rounded-triangular, c. 3 cm × 1.5 cm, with fleshy reddish orange seed coat.
• Seedling with hypogeal germination, cotyledons remaining enclosed in the seed coat; epicotyl 6–10 cm long; first 2 leaves opposite, simple.

Other botanical information

Guarea comprises about 8 species in tropical Africa and about 35 in tropical America. It belongs to subfamily Melioideae tribe Guareeae and seems most closely related to Turraeanthus, which differs in its petals that are fused with the staminal tube.

Guarea laurentii

Guarea laurentii De Wild. from the Central African Republic, Gabon, Congo and DR Congo closely resembles Guarea thompsonii. Both these species have latex in the bark and obscure fine venation on the lower surface of leaves, in which they differ from Guarea cedrata. Guarea laurentii differs from Guarea thompsonii in its slightly smaller flowers and thinner walled fruit. Its wood is reportedly most similar to that of Guarea cedrata, used for the same purposes and mixed in trade. The bark is used as purgative in traditional medicine.

Guarea glomerulata

Several Guarea spp. in tropical Africa are understorey shrubs or small trees, of which wood is only available in small dimensions. One of these is Guarea glomerulata Harms, occurring from south-eastern Nigeria to Gabon and DR Congo; its reddish brown wood is occasionally used for small objects.

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; 24: intervessel pits minute (≤ 4 μm); 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; 65: septate fibres present; (66: non-septate fibres present); 69: fibres thin- to thick-walled.
• Axial parenchyma: 83: axial parenchyma confluent; 85: axial parenchyma bands more than three cells wide; 86: axial parenchyma in narrow bands or lines up to three cells wide; 92: four (3–4) cells per parenchyma strand; 93: eight (5–8) 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.
• Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells; (159: silica bodies present); (160: silica bodies in ray cells).

(E. Ebanyenle, A.A. Oteng-Amoako & P. Baas)

Growth and development

Initial growth of seedlings is slow. When they are exposed to more sunlight after one year, growth may speed up. However, planted trees in Nigeria reached on average only 10 m in height and 20 cm in diameter after 25 years, and it has been estimated that it takes about 200 years for Guarea thompsonii trees to reach 100 cm in bole diameter. Fruits mature about 6 months after flowering. In Côte d’Ivoire fruiting is in August and in December. Birds such as hornbills, monkeys, duiker and porcupines eat the fleshy seed coat and may disperse the seeds.

Ecology

Guarea thompsonii occurs in lowland evergreen rainforest, usually primary forest. In Ghana it is most common in moist evergreen forest, especially in undisturbed forest, but it occurs also in moister types of semi-deciduous forest. It reaches its highest density in flat but well-drained sites. Guarea thompsonii is classified as a shade-bearer. In the forest, seedlings are most common in the shade, although generally less common than those of Guarea cedrata. For proper development of seedlings, some opening of the forest canopy seems essential.

Propagation and planting

Guarea thompsonii has comparatively large seeds, with a 1000-seed weight of about 2 kg. They have short viability. Germination is rather slow, taking 20–35 days in Côte d’Ivoire. Seedlings are drought sensitive.

Management

In general, larger trees of Guarea thompsonii occur in low densities in the forest. In Côte d’Ivoire Guarea thompsonii seems to be less common than Guarea cedrata. However, it is locally common in Ghana. In southern Cameroon the average density of boles of Guarea spp. over 60 cm in diameter is 0.03–0.14 per ha, with a wood volume of 0.16–1.22 m³/ha. In the Central African Republic the average wood volume has been recorded at 0.26–0.34 m³/ha. In Gabon Guarea thompsonii is slightly less uncommon than Guarea cedrata; the average wood volume of Guarea trees has been estimated at 0.13 m³/ha. In Congo wood volumes of up to 0.30 m³/ha have been reported.

Harvesting

The minimum bole diameter for harvesting of Guarea thompsonii is 60 cm in Côte d’Ivoire and DR Congo, 70 cm in the Central African Republic, and 80 cm in Cameroon and Liberia.

Yield

In DR Congo a tree with a bole diameter of 79 cm yielded 5.3 m³ of timber, and a tree 100 cm in diameter yielded 8.8 m³, which is less than for Guarea cedrata due to a shorter bole.

Handling after harvest

The density of the wood is often around 1000 kg/m³ before drying, which means that freshly harvested boles may sink in water; this limits the possibilities of transport by river.

Genetic resources

Guarea thompsonii is quite widespread, but usually occurs in low densities and is usually restricted to undisturbed forest. It is included in the IUCN Red list as a vulnerable species because of habitat loss and degradation, and selective felling. In general, the levels of exploitation are moderate.

Prospects

More research is needed on appropriate management systems in natural forest to ensure a sustainable exploitation of Guarea thompsonii. However, its slow growth rate is a serious drawback for larger-scale commercial exploitation, necessitating very long rotation cycles. The establishment of plantations seems unprofitable. Biosystematic research is needed to clarify whether the recorded differences between Guarea thompsonii and Guarea laurentii justify their distinction on species level. The wood properties and wood anatomy of the two species should also be considered in this research because these reportedly differ between the species.

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.

• 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.

• CTFT (Centre Technique Forestier Tropical), 1961. Résultats des observations et des essais effectués au Centre Technique Forestier Tropical sur bossé, Guarea cedrata Pellegr., mutigbanaye, Guarea thompsonii Sprague & Hutch. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 7 pp.

• CTFT (Centre Technique Forestier Tropical), 1978. Bossé. Bois et Forêts des Tropiques 177: 35–49.

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

• Farmer, R.H., 1972. Handbook of hardwoods. 2nd Edition. Her Majesty’s Stationery Office, London, United Kingdom. 243 pp.

• 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.

• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.

• Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays Bas. pp. 465–1271.

Other references

• ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.

• Aubréville, A., 1959. La flore forestière de la Côte d’Ivoire. Deuxième édition révisée. Tome deuxième. Publication No 15. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 341 pp.

• CIRAD Forestry Department, 2003. Bosse. [Internet] Tropix 5.0. http://tropix.cirad.fr/ame/bosse.pdf. February 2008.

• CTFT (Centre Technique Forestier Tropical), 1951. Bossé. I – Fiche botanique et forestière. Bois et Forêts des Tropiques 20: 251–254.

• 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.

• Fouarge, J., Sacré, E. & Mottet, A., 1950. Appropriation des bois congolais aux besoins de la métropole. Série Technique No 38. Institut National pour l’Étude Agronomique du Congo belge (INEAC), Brussels, Belgium. 17 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.

• InsideWood, undated. [Internet] http://insidewood.lib.ncsu.edu/search/. May 2007.

• Keay, R.W.J., 1958. Meliaceae. In: Keay, R.W.J. (Editor). Flora of West Tropical Africa. Volume 1, part 2. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 697–709.

• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.

• Normand, D., 1955. Atlas des bois de la Côte d’Ivoire. Tome 2. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 132 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.

• Staner, P. & Gilbert, G., 1958. Meliaceae. 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 7. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 147–213.

• Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 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.

• World Conservation Monitoring Centre, 1998. Guarea thompsonii. In: IUCN. 2007 IUCN Red List of Threatened Species. [Internet] http://www.iucnredlist.org. February 2008.

Sources of illustration

• Aubréville, A., 1959. La flore forestière de la Côte d’Ivoire. Deuxième édition révisée. Tome deuxième. Publication No 15. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 341 pp.

• Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays Bas. pp. 465–1271.

• 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)

• R.H.M.J. Lemmens, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article

Lemmens, R.H.M.J., 2008. Guarea thompsonii Sprague & Hutch. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 24 September 2023.

• See the Prota4U database.