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H. G. Richter and M. J. Dallwitz

Eusideroxylon zwageri Teijsm. & Binnend. (Billian, ulin)

Nomenclature etc. LAURACEAE. A second species, Eusideroxylon melagangai Sym., was relegated to the monotypic genus Potoxylon by Kostermans. The wood of this species endemic to Borneo differs from 'billian' by a lower density (0.70–0.80 g/cm³), lower rays (around 0.7 mm), fibres occasionally septate, oil cells also associated with rays. Trade and local names: Borneo ironwood, billian (GB); bilian, bois de fer (FR); belian, tambulian, im muk (MY); belian, onglen, tulian, tebelian, ulin (ID); tambulian, sakian, biliran (PH). Not protected under CITES regulations.

Tree. Geographic distribution: Indomalesia.

General. Growth ring boundaries indistinct or absent. Heartwood basically brown to yellow, without streaks. Sapwood colour distinct from heartwood colour. Odour indistinct or absent. Density 0.85–1.1 g/cm³. Heartwood with yellowish to greenish (olive) hues when fresh, dark brown to almost black upon exposure.

Vessels. Wood diffuse-porous. Vessels arranged in no specific pattern, in multiples, commonly short (2–3 vessels) radial rows. Average tangential vessel diameter 150–230(–280) µm; diameter of vessel lumina: large to very large. Average number of vessels/mm² 2–7(–10); vessels per square millimetre very few to few. Perforation plates simple. Intervessel pits alternate, average diameter (vertical) 8–11 µm, medium. Vessel-ray pits with distinct borders or with reduced borders or apparently simple, similar to intervessel pits, rounded or angular to horizontal to vertical. Tyloses in vessels present, thinwalled or sclerotic.

Tracheids and fibres. Fibres very thick-walled. Average fibre length 1200–1900 µm. Average fibre length medium to long. Fibre pits mainly restricted to radial walls, simple to minutely bordered. Fibres non-septate.

Axial parenchyma. Axial parenchyma not banded. Axial parenchyma paratracheal. Paratracheal axial parenchyma aliform to confluent. Aliform parenchyma lozenge. Axial parenchyma as strands. Average number of cells per axial parenchyma strand 4–9.

Rays. Rays 8–10 per tangential mm, multiseriate (also if only few), 2–3(–4) cells wide, narrow (2–3 seriate) to of medium width (3–5 seriate). Height of large rays commonly 500 to 1000 µm to commonly over 1000 µm (occasionally up to 3 mm high). Rays composed of a single cell type (homocellular), or two or more cell types (heterocellular); homocellular ray cells procumbent. Heterocellular rays with square and upright cells restricted to marginal rows, mostly 1 marginal row of upright or square cells.

Storied structures. Storied structure absent.

Secretory structures. Oil and mucilage cells present (oil cells), associated with axial parenchyma.

Mineral inclusions. Crystals not observed. Silica not observed.

Illustrations. • Transverse section. Eusideroxylon zwageri. • Tangential section. Eusideroxylon zwageri. • Radial section. Eusideroxylon zwageri.


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’.

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