Nomenclature etc. DIPTEROCARPACEAE. Trade and local names: upun, upun batu, penyau (MY); balau penyau, cangal tanduk, penyau tanduk (ID). Not protected under CITES regulations.
Tree. Geographic distribution: Indomalesia (endemic to Borneo).
General. Growth ring boundaries indistinct or absent. Heartwood basically brown red green. Sapwood colour distinct from heartwood colour. Density 0.85–1 g/cm³.
Vessels. Wood diffuse-porous. Vessels arranged in no specific pattern, exclusively solitary. Average tangential vessel diameter 160–220 µm; diameter of vessel lumina: large to very large. Average number of vessels/mm² 5–11; vessels per square millimetre few. Perforation plates simple. Intervessel pits alternate, average diameter (vertical) 4–6 µm, small, vestured. Vessel-ray pits with reduced borders or apparently simple, rounded or angular. Tyloses in vessels present, thinwalled.
Tracheids and fibres. Fibres very thick-walled. Average fibre length 1200–2000 µm. Average fibre length medium to long. Fibre pits common in both radial and tangential walls, distinctly bordered. Fibres non-septate.
Axial parenchyma. Axial parenchyma apotracheal and paratracheal. Apotracheal axial parenchyma diffuse and diffuse-in-aggregates. Paratracheal axial parenchyma scanty and vasicentric. Axial parenchyma as strands. Average number of cells per axial parenchyma strand 5–10.
Rays. Rays 6–12 per tangential mm, multiseriate (also if only few), 3–4(–6) cells wide, of medium width (3–5 seriate). Rays of two distinct sizes. Height of large rays commonly 500 to 1000 µm to commonly over 1000 µm (up to 1.5 mm high). Rays composed of two or more cell types (heterocellular). Heterocellular rays with square and upright cells restricted to marginal rows, mostly 2–4 marginal rows of upright or square cells. Sheath cells present.
Secretory structures. Intercellular canals present, non-traumatic origin, axial type, diffusely arranged. Intercellular canals rather large (100–230 µm) and therefore easily mistaken for vessels.
Mineral inclusions. Crystals not observed. Silica not observed.
Illustrations. • Transverse section. Upuna borneensis. Axial intercellular canals (IC). IC. IC. IC. IC. IC. • Tangential section. Upuna borneensis. • Radial section. Upuna borneensis.
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. http://delta-intkey.com’.