Common Name

Artesian Range Whorled Wattle

Family

Fabaceae

Distribution

Occurs in a relatively restricted area of the W Kimberley region of northern W.A. where it is known from the Edkins Ra. and Artesian Ra., near the Charnley R.

Description

Erect shrub 0.4–1 m tall. Branchlets pubescent to short-pilose with straight, patent, white hairs. Stipules 1–1.5 (–2) mm long, wide-spreading. Phyllodes 11–18 per whorl, dimorphic, the uppermost phyllodes subtending inflorescences 2–5 mm long with mucro 2–3 mm long, the lowermost phyllodes in vegetative region 6–20 mm long with slender, brittle mucro 0.5–1.5 mm long, straight to shallowly incurved but commonly shallowly recurved at apex, sub-terete to flat, hirsutulous; longitudinal nerves not visible. Peduncles 15–25 mm long, indumentum as on branchlets; heads 25–40-flowered. Bracteoles lanceolate to narrowly lanceolate, c. 1.5 mm long and 0.3 mm wide. Flowers 5-merous; calyx 1/3–2/5 length of corolla, dissected for 1/4–1/2 its length into oblong or triangular lobes, calyx tube glabrous; petals striate but often obscurely so, glabrous. Pods ±sessile, 2.5–9 cm long, 5–7 mm wide, flat but raised over seeds along midline, reticulately nerved. Seeds longitudinal, irregularly obloid-ellipsoid, black, dull and smooth except slightly shiny and often wrinkled at centre, aril clavate.

Phenology

A short-lived species that regenerates prolifically following fire. Flowers Mar.–June. and Aug.–Oct.; immature pods often occurring with flowers; mature seed collected in Apr.

Habitat

Grows on red-grey sand over quartzite or sandstone on slopes and rocky ridges, in sand seeps and along seasonal creeks.

Specimens

W.A.: [localities withheld for conservation reasons.] 20 Mar. 1998, M.D. Barrett MDB 446 (PERTH); 11 Apr. 2013, R.L. Barrett, M.D. Barrett & B. Anderson RLB 7948 (PERTH); 22 June 2012, H. Dauncey H 611 (PERTH).

Notes

Very closely related to the poorly known A. smeringa which grows in the northern Packhorse Ra., c. 80 km SE of where A. dimorpha occurs. Acacia smeringa is recognized by its phyllodes in the vegetative region of the branchlets being shorter than those of A. dimorpha (5–7 mm long) and its calyx longer (½–2/3 length of the petals); see B.R.Maslin, M.D.Barrett & R.L.Barrett, Nuytsia 23: 581 (2013) for further details. Future studies may consider it is better to treat A. dimorpha as a subspecies of A. smeringa. Acacia dimorpha is also closely related to A. prolata. These three species grow relatively close to one another within a geologically complex area that contains many localised plant species. A few specimens may possibly be intermediates; for example, R.L.Barrett 619 (PERTH) from the Caroline Ra. is vegetatively similar to A. dimorpha but it has the calyx of A. smeringa (this specimen was noted by A.S.George, Fl. Australia 11B: 394, 2001, as a variant of A. smeringa) and R.L. & M.D.Barrett RLB 6766 (PERTH) from Mt Russ (NW of Caroline Ra.) appears to combine characters of both A. smeringa and A. dimorpha.

Conservation

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

FOA Reference

Flora of Australia Project

Author

B.R.Maslin