Common Name

Lawley River Wattle

Family

Fabaceae

Distribution

Occurs near the mouth of the Lawley R. in the Kimberley region of northern W.A. where it is known from only a single large population over several kilometres.

Description

Erect shrub 1.5–2 m tall. Branchlets hirsutulous with fine, short, patent, straight, gland-tipped and eglandular hairs. Stipules persistent, 2–3 mm long, slender, subulate, curved upwardly from base, not or scarcely fused at their base. Phyllodes inaequilaterally obtriangular, upper margin obviously rounded or more commonly with a ±sharp angle above the middle at the gland, lower margin ±straight, pungent by a slender, rigid cusp 0.5–0.7 mm long, 3–5 mm long, 2–3 mm wide, l: w = 1.5–2, green, indumentum similar to branchlets; longitudinal nerves 6–8, sometimes rather indistinct; gland 3–4 mm above the pulvinus, often at apex of marginal angle, tiny but evident a ´10 mag. Peduncles 10–12 mm long, indumentum as on branchlets, with a persistent bract just below the spike; spikes short-cylindrical, 7–10 mm long (when dry). Bracteoles 1.5–2 mm long, exserted in buds. Flowers 5-merous; sepals 2/3–3/4 length of the petals, united at extreme base, linear. Pods narrowly oblong, 2–5 cm long, (4–) 5 mm wide, curved, low-rounded over seeds, hirsutulous by fine, patent, very short, eglandular hairs intermixed with larger, gland-tipped hairs with inflated, septate stalks. Seeds longitudinal, arillate.

Phenology

The single fertile specimen was collected in late Mar. and possessed young and near-mature inflorescence buds, a few spikes at anthesis and a few pods with seeds.

Habitat

Grows on sand over sheet sandstone.

Specimens

W.A. [locality withheld for conservation reasons] R.L.Barrett & M.D.Barrett RLB 6464 (PERTH).

Notes

Acacia obtriangularis belongs to the ‘A. deltoidea group’ but is distinguished from all other members of this group by its spicate inflorescences. It appears closest to A. froggattii and A. vincentii which are both further distinguished by their fewer-nerved phyllodes that that are more uniformly rounded along their upper margins (not angled at the gland which is normally more obscure or sometimes absent); see B.R.Maslin, M.D.Barrett & R.L.Barrett, Nuytsia 23: 569–570 (2013), for further discussion.

Conservation

Acacia obtriangularis 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