Acacia olgana Maconochie, J. Adelaide Bot. Gard . 1: 183; 184, fig. 4 (1978)
Mount Olga Wattle
Shrub or small tree to 6 (sometimes 15) m high. Bark rough, slightly fissured, grey or grey-brown. Branchlets angular or flattened towards apices, light brown to reddish, mostly glabrous. Phyllodes linear to very narrowly elliptic, flat, often curved at apex, 6–18 cm long, 2–7 (–10) mm wide, coriaceous, the margins sometimes reddish, golden-pubescent when young, soon becoming glabrous, with 1 prominent central nerve, the minor parallel nerves 6–11 per mm, nonanastomosing; gland 1, basal, inconspicuous, to 5 mm above pulvinus. Spikes 1.5–4 cm long, densely flowered, bright or golden yellow. Flowers 5-merous; calyx 0.5–1 mm long, dissected to at least 4/5, spathulate, densely villous; corolla 1.25–1.75 mm long, dissected to 2/5–1/2, glabrous; ovary glabrous or tomentose towards apex. Pods linear, straight to slightly curved, 3.5–10 cm long, mostly 3–5 mm wide, chartaceous to coriaceous, glabrescent; margins nerve-like. Seeds longitudinal to slightly oblique, broadly oblong to broadly elliptic, dorso-ventrally flattened, 3.1–5 mm long, dark brown; areole small, pale.
Occurs in far central-eastern W.A., Ayers Rock area and the Olgas in south-western N.T. and several hilly ranges in north-western S.A. The herb. NSW specimen, Coward Springs, due W of Lake Eyre, S.A., Knox College Expedition no. 7 (partim), is distributionally anomalous and may well represent an error; the area comprises chenopod plains dotted with mound springs, an unlikely habitat for A. olgana. Often grows along watercourses, in gorges, crevices on rocky ranges, on sedimentary or conglomerate rocks, sometimes on sand dunes, in shrubland and woodland. Flowers May–Sept.
This species has distinctively smooth, narrow, chartaceous mature pods. An allied taxon has been separated from A. olgana on the basis of having slightly broader (to 7 mm wide), sparsely to mid-villous mature pods, larger seeds and shorter phyllodes with reddish, often resinous crenulate margins, e.g. 1 km N of Kulgera, N.T., R.B.Hadlow 166 & A.B.Court (CANB, NSW); 1 km E of Kulgera, N.T., P.K.Latz 5843 (BRI, DNA, NSW, NT, PER); Everard Park, S.A., P.L.Milthorpe 3107 (NSW); slopes of Mt Illbillee, eastern end of Everard Ra., S.A., G.C.Cornwall 171 (AD, NSW). Further investigation of these taxa is required.
Type of accepted name
Central Amphitheatre, Valley of Heads, at Mt Olga, N.T., 4 July 1958, R.Hill & T.R.N.Lothian 791 ; holo: NT n.v. ; iso: AD n.v ., K n.v.
Racosperma olganum (Maconochie) Pedley, Bot. J. Linn. Soc. 92: 249 (1986). Type: as for accepted name.
J.R.Maconochie, loc. cit. ; M.Simmons, Acacias Australia 2: 251 (1988); A.Urban, Wildfl. & Pl. Centr. Australia 83 (1990); D.J.E.Whibley & D.E.Symon, Acacias S. Australia 2nd edn, 252 & 253 (1992).
W.A.: between Thryptomene Hill and Mt Samuel on Gunbarrel Hwy, D.J.Edinger 106 (PERTH). N.T.: Valley of the Winds, Mt Olga, B.G.Briggs 3526a (CANB, NSW); Olga Gorge, J.R.Maconochie 1931 & 2532 (BRI, DNA, NSW, NT, PERTH) . S.A.: Musgrave Ra., 12 July 1969, F.T.Turvey (AD, NSW, PERTH).