Commercial Timbers


H. G. Richter and M. J. Dallwitz

Grevillea robusta A.Cunn. (Silky oak)

Nomenclature etc. PROTEACEAE. Not protected under CITES regulations.

Description based on 3 specimens. Tree. Geographic distribution: Australia and tropical South America.

General. Growth ring boundaries indistinct or absent. Heartwood basically brown and yellow, without streaks. Sapwood colour distinct from heartwood colour. Odour indistinct or absent. With conspicuous silver grain (high rays).

Vessels. Vessels present. Wood diffuse-porous. Vessels arranged in tangential bands and no specific pattern, in multiples, commonly in clusters. Vessel outline rounded. Two distinct vessel diameter classes absent. Vessels often grouped in clusters or short tangential rows. Average tangential vessel diameter 100–140–200 µm; diameter of vessel lumina: large. Average number of vessels/mm² 7–10; vessels per square millimetre few. Perforation plates simple. Intervessel pits alternate, average diameter (vertical) 6–8 µm, small and medium, not vestured. Vessel-ray pits with distinct borders, similar to intervessel pits, of uniform size or type, of the same type in adjacent elements, located throughout the ray. Helical thickenings present, only in narrow vessel elements, throughout the body of vessel elements. Tyloses in vessels absent. Other deposits in heartwood vessels present, brown organic deposits.

Tracheids and fibres. Vascular or vasicentric tracheids sporadic to absent. Fibres of medium wall thickness. Fibre pits common in both radial and tangential walls, simple to minutely bordered and distinctly bordered. Helical thickenings absent. Fibres non-septate.

Axial parenchyma. Axial parenchyma present, banded. Axial parenchyma bands not marginal (or seemingly marginal), scalariform, coarse, more than three cells wide. Axial parenchyma paratracheal. Paratracheal axial parenchyma unilateral. Axial parenchyma as strands. Average number of cells per axial parenchyma strand 2–4(–6).

Rays. Rays present, 1 per tangential mm, multiseriate (also if only few), 1–15 cells wide, very wide (more than 10 seriate). Rays with multiseriate portions as wide as uniseriate portions absent. Aggregate rays absent. Rays of two distinct sizes. Height of large rays commonly over 1000 µm. Rays composed of a single cell type (homocellular) and 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. Sheath cells present. Tile cells absent. Perforated ray cells absent. Disjunctive ray parenchyma end walls indistinct or absent.

Storied structures. Storied structure absent.

Secretory structures. Oil and mucilage cells absent. Intercellular canals absent. Laticifers or tanniniferous tubes absent.

Cambial variants. Included phloem absent. Other cambial variants absent.

Mineral inclusions. Crystals not observed. Cystoliths absent. Silica not observed.

Physical and chemical tests. Heartwood not fluorescent. Water extract fluorescent; basically colourless to brown or shade of brown. Heartwood extractives not leachable by water. Ethanol extract fluorescent. Colour of ethanol extract yellow or shade of yellow. Weak yellowish fluorescence of water and ethanol extracts. Chrome azurol-S test positive. Froth test negative. Splinter burns to full ash. Ash other than white, grey, yellow or brown.

Illustrations. • Transverse section. Grevillea robusta. • Tangential section. Grevillea robusta. • Radial section. Grevillea robusta.

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.’.