Shrub to c. 0.6 m high. Branchlets normally red-brown to light brown, puberulous with antrorse to ± patent hairs. Stipules setaceous to narrowly triangular, 2.5–4 mm long. Phyllodes often crowded, patent, narrowly semi-trullate with a prominent gland-angle on adaxial margin near base, 6–8 mm long, 1.5–2.5 mm wide, acuminate, pungent, with slender, c. 1 mm long cusp, rigid, green, glabrous; midrib prominent, central; lateral veins absent. Inflorescences simple, 1 per axil; peduncles 5–10 mm long, puberulous; heads globular, 4-flowered, pale yellow. Flowers 4-merous; sepals united. Pods terete, narrowed at both ends, curved, to 7.5 cm long and 3.5 mm wide, red-brown, striate, subglabrous. Seeds longitudinal, obloid, 4–5 mm long; aril terminal, conical.

Flowers May–August.

Native.

This species occurs in southwestern Western Australia in the Darling Range from the Helena Valley S to the Serpentine River, and is also recorded from the adjacent coastal plain at Maddington.

In the Darling Range it grows on rocky hillsides in Eucalyptus woodland.

Conservation Code Three in Western Australia.

W.A.: Serpentine, B.R. Maslin 4175 (PERTH); Maddington, 6 Aug. 1904, A. Morrison s.n. (K, PERTH); Helena Valley, end [of] Moola Rd, J. Seabrook 13 (PERTH).

Acacia horridula Meisn., in J.G.C. Lehmann, (ed.) Plantae Preissianae 1(1): 9 (1844); Acacia horridula Meisn. var. horridula (autonym), F.L.E. Diels & E.G. Pritzel, Botanische Jahrbucher fur Systematik, Pflanzengeschichte und Pflanzengeographie 35(2–3): 297 (1904); Racosperma horridulum (Meisn.) Pedley, Austrobaileya 6(3): 468 (2003). Type: "In regionibus interioribus Australiae meridionali-occidentalis, m. Nov. 1840. Herb. Preiss. No. 965, cum fruct. jun. et in arenosis ad fluv. Canning (Perth) d. 4. Dec. 1839. florescens No. 1151"; lecto: Canning R., Perth, W.A., 4 Dec. 1839, L. Preiss 1151, NY, designated by B.R. Maslin, Nuytsia 2(5): 277 (1978); isolecto: G, LD, MEL, P, PERTH (fragment ex MEL), W; excluded syn: L. Preiss 965 , see Acacia pycnocephala.

The description of Acacia horridula in G. Bentham, Flora Australiensis 2: 350 (1864) is a mixture of A. horridula (Preiss 1151), A. pycnocephala (Preiss 965) and A. semitrullata (Drummond s.n. and Oldfield s.n.). These species together with A. hastulata, A. inops and A. uliginosa comprise the 'A. horridula group', according to B.R. Maslin, Nuytsia 2(5): 270 (1978). Acacia rigida, A. phaeocalyx and A. plautella appear to have fairly close relationships to this group.

B.R. Maslin, Nuytsia 2(5): 278, fig. 5 (1978); B.R. Maslin, Flora of Australia 11A: 510, fig. 65A–C (2001).

Maslin, B.R. (1978). Studies in the genus Acacia (Mimosaceae) – 8 A revision of the Uninerves - Triangulares, in part (the tetramerous species). Nuytsia 2(5): 266–333.

Maslin, B.R. (2001). Acacia horridula, p. 508, in A.E. Orchard & A.J.G. Wilson (eds), Flora of Australia Volume 11A, Mimosaceae, Acacia part 1. (CSIRO Publishing: Melbourne).

Maslin, B.R. & Cowan, R.S. (1994). C.F. Meissner’s species of Acacia (Leguminosae: Mimosoideae): typification of the names. Nuytsia 9(3): 399–414 (1994). https://florabase.dpaw.wa.gov.au/science/nuytsia/217.pdf

Wheeler, J.R. (1987). Mimosaceae, p.p. 211–234, in N.G. Marchant, J.R. Wheeler, B.L. Rye, E.M. Bennett, N.S. Lander & T.D. Macfarlane, Flora of the Perth Region Part 1. (Western Australian Herbarium, Department of Agriculture: W.A.).

Adapted from Flora of Australia Volume 11A (2001), product of ABRS, ©Commonwealth of Australia.