Commercial Timbers


H. G. Richter and M. J. Dallwitz

Cotylelobium spp. (Resak)

Nomenclature etc. DIPTEROCARPACEAE. Cotylelobium burckii, C. lanceolatum, C. melanoxylon. Trade and local names: resak (MY); resak batu (BN); guam, resak bukit (ID); khiam (TH). Not protected under CITES regulations.

Tree. Geographic distribution: Thailand, Laos, Vietnam, Cambodia and Indomalesia.

General. Heartwood basically brown red. Sapwood colour distinct from heartwood colour. Density 0.81–1.16 g/cm³.

Vessels. Wood diffuse-porous. Vessels exclusively solitary. Average tangential vessel diameter 120–140 µm. Average number of vessels/mm² 8–10(–20) (most numerous in Cotylelobium burckii). Perforation plates simple. Intervessel pits extremely rare if at all present alternate, average diameter (vertical) 4–5 µm, vestured. Vessel-ray pits with reduced borders or apparently simple, rounded or angular (predominantly circular and very large), unilaterally compound and coarse. Tyloses in vessels present (abundant), thinwalled.

Tracheids and fibres. Fibres of medium wall thickness to very thick-walled. Average fibre length 1000–1500 µm. Fibre pits common in both radial and tangential walls, distinctly bordered.

Axial parenchyma. Axial parenchyma apotracheal, or paratracheal. Apotracheal axial parenchyma diffuse, or diffuse-in-aggregates. Paratracheal axial parenchyma vasicentric, aliform, and confluent. Aliform parenchyma winged. Axial parenchyma as strands.

Rays. Rays 6–8 per tangential mm, multiseriate (also if only few), 2–6(–8) cells wide. Rays of two distinct sizes. Height of large rays commonly over 1000 µm. Rays composed of two or more cell types (heterocellular). Heterocellular rays with square and upright cells restricted to marginal rows, mostly 1 marginal row of upright or square cells or mostly 2–4 marginal rows of upright or square cells. Sheath cells present.

Secretory structures. Intercellular canals present, axial type, diffusely arranged (sometimes grouped in small units).

Mineral inclusions. Crystals present (only in: C. melanoxylon), prismatic, located in ray cells. Crystal-containing ray cells upright and/or square. Number of crystals per cell or chamber one. Silica present, as grains, in rays cells.

Illustrations. • Transverse section. Cotylelobium melanoxylon. Note axial intercellular canals, solitary (ICs) and in tangential bands (ICb). ICs. ICs. ICs. ICb. • Tangential section. Cotylelobium lanceolatum. • Radial section. Cotylelobium lanceolatum. Note silica particles in ray cells, blow-up next illustartion. • Silica in rays. Cotylelobium lanceolatum.

The interactive key allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, summaries of attributes within groups of taxa, and geographical distribution.

Cite this publication as: ‘Richter, H.G., and Dallwitz, M.J. 2000 onwards. Commercial timbers: descriptions, illustrations, identification, and information retrieval. In English, French, German, Portuguese, and Spanish. Version: 25th June 2009.’.