Acacia orthocarpa F.Muell.
Acacia orthocarpa F.Muell.
Pilbara Weeping Wattle, Needle-leaf Wattle
Occurs in tropical Australia, in the Dampier–Sahara–Mt Anderson and Fitzroy Crossing–Gordon Downs–Wyndham areas of W.A., in mainly central N.T., and in the Lawn Hill–Mount Isa, Galilee and Georgetown–Gilberton areas of Qld.
Commonly wispy, graceful, glabrous shrub or small tree 2–6 m high, crown open with ultimate branchlets sometimes ±pendulous, single-stemmed or sparingly branched at base, sometimes multi-stemmed with bushy crown. Branchlets obscurely ribbed. Phyllodes straight to ±curved, terete to subterete (but sometimes drying irregularly quadrangular or rarely flat), (5–) 6–15 cm long (wispy form) or (1.5–) 2–6 (–7) cm long (bushy form), 0.5–0.9 mm wide, slender, not rigid, puncticulate by evident (x10 mag.) stomata, green to grey-green or sub-glaucous, sometimes lightly resinous; nerveless or very obscurely longitudinally multistriate; gland 1, inconspicuous, basal. Spikes 0.9–3.2 cm long, yellow. Flowers 5-merous; calyx gamosepalous, dissected for 1/2–4/5, thin. Pods erect, mostly linear-oblanceolate to ±linear, basally tapered, straight-sided, terete to compressed, 3–10 cm long, 3.5–5 mm wide, woody, ±straight, light brown to yellow-brown, resinous, ±longitudinally nerved, opening elastically from apex with dehisced valves shallowly recurved. Seeds retained in pods following dehiscence, longitudinal or slightly oblique and seated in distinct chambers, oblong-elliptic, 4.3–6 mm long, laterally compressed, dark brown; funicle-aril narrowly turbinate and creamy white.
Flowers (often sporadically) Apr.–Nov.
Grows on sandy flats, rocky hills and in rocky watercourses, in savannah woodland and eucalypt shrubland, often with spinifex.
W.A.: Cherrabun Stn, S of Fitzroy Crossing, J.S.Beard 6956 (NSW, PERTH); 1 mile [1.6 km] E of turnoff to Port Hedland, I.V.Newman 678 (NSW). N.T.: c. 73.6 km N of Tennant Creek, J.R.Maconochie 971 (DNA, NSW, PERTH); 61.2 km S of Dunham R. on Great Northern Hwy, M.D.Tindale 10144, P.Munns & R.Turley (BRI, DNA, MEL, MO, NSW, PERTH). Qld: Lake Moondarra, Mount Isa, R.G.Coveny 480 (CANB, NSW, US); Lawn Hill Stn, P.K.Latz 1602 (DNA, NSW).
Acacia orthocarpa is very closely related to A. arida and the relationship between the two species requires further investigation. The bushy form of A. orthocarpa is superficially similar to A. tenuissima and although the two species can easily be confused they are not particularly closely related. A rare putative hybrid between A. orthocarpa and A. ancistrocarpa occurs on Woodstock station (K.L.Tinley 3244, PERTH).
Data derived from Flora of Australia Volumes 11A (2001), 11B (2001) and 12 (1998), products of ABRS, ©Commonwealth of Australia
Revised by B.R.Maslin
Dr M.D.Tindale and Dr P.G.Kodela with the assistance of M.Bedward, S.J.Davies, C.Herscovitch, D.A.Keith and/or D.A.Morrison
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