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Letestua durissima (A.Chev.) Lecomte

Notul. Syst. (Paris) 4: 5 (1920).
Letestua floribunda Lecomte (1920).
Origin and geographic distribution
Letestua durissima is distributed in Central Africa (Cameroon, Central African Republic, Equatorial Guinea, Gabon, Congo, DR Congo).
The wood of Letestua durissima, known in the trade as ‘congotali’, is considered suitable for heavy construction and flooring, mine props, ship and boat building, vehicle bodies, sporting goods, agricultural implements, musical instruments, precision equipment, joinery, sleepers, poles and piles, toys and novelties, and pattern making. The extent of its use in tropical Africa is unknown.
A bark decoction is a component of a traditional medicine against leprosy.
Production and international trade
In 2003 the export of Letestua durissima sawnwood from DR Congo was 3000 m³ at an average price of US$ 102 per m³. Export from Cameroon is prohibited.
The heartwood is fairly dark red-brown, turning chestnut brown with age; it is distinctly demarcated from the 5–9 cm wide pale brown sapwood. The grain is usually straight, but sometimes interlocked; the texture is fine to medium.
The wood is very heavy, with a density of 1035–1130 kg/m³ at 12% moisture content. Shrinkage rates are high: 7.3–10.0% radial and 10.7–12.8% tangential from green to oven dry. Drying is slow, with high risks of distortion and checking. The dried wood is fairly stable. The low saturation point makes the wood suitable for use in humid conditions, e.g. mine work. The wood is very hard, strong, resilient and stiff. At 12% moisture content, the modulus of rupture is 230–284 N/mm², modulus of elasticity 18,900–22,800 N/mm², compression parallel to grain 91–102 N/mm², shear 10.8–17.9 N/mm², cleavage 22.4–30.4 N/mm and Chalais Meudon side hardness 10.2–19.5.
The wood is slow and difficult to saw due to the high silica content, which leads to severe blunting, and an irritating dust is produced. The wood should be sawn as fresh as possible and stellite-tipped sawteeth are recommended. Planing is relatively easy and gives a smooth surface. Pre-boring for nailing and screwing is recommended to avoid splitting, but the wood holds nails well. It glues well, when done carefully.
The durability of the wood is high. It is rarely attacked by termites, but must be treated to prevent marine borer attack. The sapwood is not susceptible to Lyctus borers. The wood is resistant to preservative treatment.
Large tree up to 50 m tall; bole branchless for up to 40 m, straight, cylindrical, up to 240 cm in diameter, base fluted or with steep buttresses; outer bark grey with rectangular scales, inner bark fibrous, pink, exuding a white latex; branches thick, covered with scars from fallen leaves, young branches glabrous, terminal buds glandular. Leaves arranged spirally, clustered at the ends of branches, simple and entire; stipules absent; petiole 3–4 cm long, grooved near blade; blade obovate-oblong, 16–24 cm × 5–10 cm, cuneate at base, rounded at apex, leathery, upper surface shiny, pinnately veined with 12–17 pairs of lateral veins. Flowers in fascicles in the leaf axils, bisexual, regular; pedicel c. 2 cm long, glabrous; sepals in 2 whorls of (2–)3, hairy outside, glabrous inside; corolla with a short tube and 12–18 lobes c. 3.5 mm long, each lobe with 2 large lateral appendages, white, glabrous; stamens opposite each corolla lobe; ovary superior, 16–18-celled. Fruit an ovoid-elongate fleshy berry 5–8 cm long, indehiscent, 1-seeded. Seed ellipsoid, compressed, c. 3.5 cm × 1 cm × 1 cm, tapering at both ends, with linear scar c. 3 cm long, seed coat woody, shiny brown. Seedling with epigeal germination.
In Gabon Letestua durissima flowers in December. In Congo the fruits ripen in October–November.
Letestua comprises a single species.
Letestua durissima occurs scattered in primary rainforest.
Germination is about 100% in 7–30 days when fresh seeds are used.
Genetic resources and breeding
It is unclear to what extent Letestua durissima is threatened by genetic erosion. Although it is not included in the IUCN Red list of threatened species, caution is warranted for a species of primary rainforest with limited distribution.
Because of its strength and durability, the wood of Letestua durissima is particularly suitable for heavy construction purposes, but sustainable production methods seem difficult to develop because of its probable slow growth and ecological requirements.
Major references
• ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.
• Aubréville, A., 1961. Sapotacées. Flore du Gabon. Volume 1. Muséum National d’Histoire Naturelle, Paris, France. 162 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.
• Pennington, T.D., 1991. The genera of Sapotaceae. Royal Botanic Gardens, Kew, Richmond, United Kingdom and the New York Botanical Garden, New York, United States. 295 pp.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.
Other references
• CIRAD Forestry Department, 2003. Congotali. [Internet] Tropix 5.0. afr/congotali.pdf. Accessed June 2006.
• 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. & Gérard, G., 1964. Bois du Mayumbe. Institut National pour l’Etude Agronomique du Congo (INEAC), Brussels, Belgium. 579 pp.
• ITTO, 2006. Annual review and assessment of the world timber situation 2005. International Timber Trade Organisation, Yokohama, Japan. 214 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.
• Pangou, S.V. & Ilengo-Boumba, S., 1984. Production de plants d’essences de forêt dense: congotali et ilomba. Centre Technique Forestier Tropical, Centre du Congo, N’Gaoua 2, Congo. 9 pp.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 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.
M. Brink
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
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:
Brink, M., 2007. Letestua durissima (A.Chev.) Lecomte. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
base of bole