Cotylelobium spp. (Resak)
Nomenclature etc. DIPTEROCARPACEAE. Cotylelobium burckii, C. lanceolatum, C. melanoxylon. Trade and local names: resak (MAL); resak batu (BRU); guam, resak bukit (RI); khiam (T). Status of protection under CITES regulations: not protected.
Tree. Geographic distribution: Thailand, Laos, Vietnam, Cambodia and Indomalesia.
General. Heartwood basically brown red. Sapwood colour distinct from heartwood colour. Basic specific gravity 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 frequent 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, or 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. Height of large rays commonly over 1000 µm. Rays composed of two or more cell types. Heterocellular rays square and upright cells restricted to marginal rows. Number of marginal rows of upright or square cells 1, or 2–4. 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.
Cite this publication as: H. G. Richter and M. J. Dallwitz (2000 onwards). 'Commercial timbers: descriptions, illustrations, identification, and information retrieval.' In English, French, German, and Spanish. Version: 4th May 2000. http://biodiversity.uno.edu/delta/.
Dallwitz (1980) and Dallwitz, Paine and Zurcher (1993 onwards, 1995 onwards, 1998) should also be cited (see General references).