Common Name

Mount Augustus Rock Wattle

Family

Fabaceae

Distribution

Restricted to Mt Augustus, 195 km NE of Gascoyne Junction, W.A.

Description

Multi-stemmed shrub 2–3 (–5) m tall and 3–6 (–8) m wide, main stems rather contorted. Bark dark grey. Branchlets normally glabrous. New shoots resinous, brown, young phyllodes silvery sericeous. Phyllodes narrowly elliptic to oblong-elliptic, (3–) 4–8 cm long, 8–20 mm wide, apices acute to obtuse and innocuous, straight, often slightly twisted or undulate; multi-striate by numerous, very fine, parallel, non-anastomosing nerves 5–10 per mm; marginal nerve discrete, light yellow aging light brown, sometimes scurfy white; gland basal. Inflorescences simple; peduncles 2–4 mm long; spikes 10–20 mm long; bracteoles 1–1.5 mm long, with linear claws and short, distinct, ±thickened laminae. Flowers 5-merous, ±resinous; sepals ±free, similar to bracteoles except laminae smaller. Pods narrowly oblong, 5.5–7.5 cm long, 8–11 mm wide, firmly crustaceous to ±woody, shiny, normally glabrous; margins with a vertical flange 2–4 mm wide. Seeds oblique, 4.5–5 mm long, dark brown except yellowish bordering pleurogram; aril white to cream aril.

Phenology

Flowers in July; mature pods Aug. and Sept.

Habitat

Grows on steep, granite slopes on skeletal sand in low open shrubland over Spinifex (Triodia sp.).

Notes

Related to A. quadrimarginea which has narrower phyllodes that are acute, commonly shallowly falcate and which possess a normally red or brown, resinous marginal nerve, and larger seeds that are longitudinal in the pods. Phyllodes resemble some forms of the seemingly parapatric A. kempeana which has longer peduncles. Clearly united sepals and chartaceous pods that are not flanged on their margins.

Conservation

Acacia petricola is listed as Priority Two under Department of Parks and Wildlife Conservation Codes for Western Australian Flora.

Author

B.R. Maslin