Acacia elachantha

Acacia elachantha M.W. McDonald & Maslin, Austral. Syst. Bot . 10: 311; 312, fig. 3 & 314, fig. 4 (1997)

Spindly shrub 2–3 m high, rarely a tree 5–6 (–8) m high; crown sparsely foliaged. Branchlets angled at extremities becoming terete with age, glabrous or minutely sericeous. New shoots glabrous or sericeous with yellow or silver hairs. Phyllodes shallowly to strongly falcate, 8–19.5 cm long, 7–22 mm wide, coriaceous, either glabrous and lightly pruinose or minutely sericeous; longitudinal nerves numerous, 2–4 per mm, with normally 3 more prominent than the rest and the lowermost 2 running together at base of phyllode, minor nerves occasionally anastomosing. Inflorescences 1 or 2 per axil, simple or vestigial binate racemes with axes to 1 mm long; peduncles 3–12 mm long, hairy or glabrous; spikes 1.5–3.3 cm long, light golden; bracteoles spathulate, 0.5 mm long. Flowers 5-merous; sepals united; ovary hairy or glabrous. Pods linear, straight to shallowly curved, 3–3.5 mm wide, chartaceous to coriaceous, glabrous to very sparsely minutely hairy. Seeds longitudinal, ±oblong, 3.5–4 mm long, glossy, dark brown to black; aril yellow. 4 n = 52, G.F.Moran et al. , in A.P.N.House & C.E.Harwood (eds), Austral. dry-zone acacias for human food 74–81 (1992).

Occurs mainly in the tropical arid zone region between latitudes 17°–24° S, extending from the Pilbara and Kimberley regions in W.A. across N.T. to central and south-western Qld. and far north-eastern S.A. (on Cordillo Downs Stn). Grows mainly on red sand plains, run-on sites associated with low rocky hills or lateritic plains. Flowers May–Aug.

Two variants, distinguished mainly on the presence or absence of indumentum, were recognised by M.W.McDonald & B.R.Maslin, op. cit. 303–320 . The main distinguishing features of these variants are:

Typical variant. Branchlets and phyllodes sparsely to densely sericeous, sometimes aging glabrous; new shoots silvery- or golden-sericeous; ovary hairy.

Glabrous variant. Branchlets glabrous, commonly pruinose at extremities; phyllodes, new shoots and ovaries glabrous.

The typical variant is more widely distributed and more commonly collected than the glabrous variant. 

Further study is required to resolve the taxonomic relationships and status of these variants.

Acacia elachantha is closely allied to, and previously confused with, A. cowleana and the two could be considered cryptic species . Apart from its mainly creek bank habitat and its more southerly distribution, A. cowleana is distinguished from A. elachantha by its more robust habit and foliage, its resinous new shoots, its longer spikes with larger flowers and its wider pods. The differences between these two species and their closest relatives, A. colei , A. leptocarpa , A. longispicata , A. thomsonii and hybrids involving A. colei x A. elachantha (typical variant) and A. elachantha (glabrous variant) x A. gonoclada are documented in M.W.McDonald & B.R.Maslin, op. cit. 303–320 . Also related to A. holosericea and its allies.

Acacia elachantha is a fast growing, short-lived species that produces prolific quantities of seed. Introduced into parts of west Africa (as A. cowleana ) since the early 1980s for fuelwood, soil rehabilitation and more recently for the use of its seeds as an alternative food. Based on allozymes, populations of A. elachantha have almost no genetic differentiation either within or between populations (Moran et al. op. cit. 78–79; referred to as A. cowleana ). This study also found that glasshouse-grown progeny were genetically identical to the parents suggesting A. elachantha has allopolyploid origins and/or an apomictic breeding system. Hybridisation between A. elachantha and A. neurocarpa (cited as the diploid race of A. holosericea ) was also suggested as the origin of the hexaploid species A. colei .

Further details on the ecology and utilisation of A. elachantha (referred to as A. cowleana ) are given in J.C.Doran & J.W.Turnbull (eds), Austral. Trees & Shrubs: species for land rehabilitation and farm planting in the tropics 134–135 (1997) and by P.Latz, Bushfires & Bushtucker 94 (1995).

Type of accepted name

14 km W of Cuddapan turn-off along Birdsville–Windorah road (71.8 km E of Betoota), Qld, 3 July 1995, M.McDonald & P.A.Butcher 57 ; holo: PERTH; iso: BRI.

Synonymy

[ A. cowleana auct. non Tate: L.Pedley, Austrobaileya 1: 171 (1978); B.R.Maslin & L.A.J.Thomson, Austral. Syst. Bot . 5: 729–743 (1992)]

Illustrations

B.R.Maslin & M.W.McDonald, A key to useful Australian acacias for the seasonally dry tropics 36–37 (1996); M.W.McDonald & B.R.Maslin, op. cit. 312, fig. 3.

Representative collections

W.A.: 10 miles [16 km] N of Sturt Creek Stn , J.S.Beard 5624 (PERTH); 11.6 km W of Kiwirrkurra , G.J.Morse 2557 (PERTH). N.T.: 28 km N of Daly Waters township turnoff on Stuart Hwy, B.R.Maslin 7410, M.McDonald & G.Leach (CANB, DNA, PERTH). Qld: 5 miles [8 km] SE of ‘Arrabury’ on ‘Lake Pure’ road , J.Pickard 1768 (K, NSW). S.A.: Cordillo Downs Stn, P.E.Conrick 2231 (AD, PERTH).

(MWM)

Top