Botanical name

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

Description

Spindly shrubs 1-3 m high but sometimes forming large shrubs or small trees 5-6 (-8) m high, main branches ascending to erect, crowns normally open and spreading with the sparse foliage confined to the ends of the branches. Bark grey, thin, smooth except longitudinally fissured at base of main stems. Branchlets angled at extremities, soon terete, minutely sericeous, rarely glabrous. New shoots usually sericeous with yellow or silvery-white hairs (sometimes with scattered microscopic resin hairs intermixed). Phyllodes shallowly to strongly uniformly falcately recurved over their entire length, 8-19.5 cm long, 7-22 mm wide, coriaceous, wide-spreading or spreading-erect, usually moderately to densely minutely sericeous with minute, closely appressed hairs, hairs sparser or absent with age, silvery to silvery blue or silvery green (colour variation probably related to density of indumentum); parallel longitudinal nerves numerous, the nerves ąwidely spaced (2-3 per mm), with normally 3 more prominent than the rest and the lowermost 2 running together at base of phyllode (but normally remaining free from the lower margin), with a few of the minor nerves forming longitudinally-orientated anastomoses, the nervation not prominent and often obscured by the dense indumentum; apex sub-acute to rounded-obtuse and terminated by a discrete callose point 0.5-1 mm long. Gland absent from apex of phyllodes. Inflorescences (1-) or, more commonly, 2 simple or vestigial binate racemes within axil of phyllodes, with axes to 1 mm long; peduncles 3-8 (-12) mm long, appressed-hairy or glabrous; spikes 15-33 mm long, light golden, flowers sub- densely arranged within the spikes. Flowers 5-merous; calyx very shallowly dissected into broadly triangular lobes; petals glabrous. Pods linear, moderately to prominently raised over seeds and slightly to moderately constricted between them, 4-8 (-11) cm long, 3-3.5 (-4) mm wide, chartaceous to coriaceous, straight to shallowly curved, glabrous to sparsely hairy with minute, straight, appressed hairs (not readily visible to unaided eye), red-brown to rich dark brown. Seeds longitudinal in the pods, ąobloid, (3-) 3.5-4 (-5) mm long, glossy, dark brown to black; aril bright yellow.

Characteristic features

Branchlets minutely sericeous. New shoots sericeous with yellow or silver hairs (sometimes with scattered microscopic resin hairs intermixed). Phyllodes uniformly shallowly to moderately falcately recurved, large (8-19.5 cm long, 7-22 mm wide), wide-spreading or spreading-erect, silvery to silvery blue or sometimes green, with many longitudinal nerves which are ąwidely spaced (the minor nerves ąsparsely longitudinally anastomosing), 2 of the 3 more prominent nerves running together at base of the phyllode. Gland absent from apex of phyllodes. Spikes rather long (15-33 mm), light golden, the flowers sub- densely arranged; petals glabrous. Pods linear, straight to shallowly curved, 3-3.5 (-4) mm wide, thin textured. Seeds very dark brown to black with a bright yellow aril.

Distribution and ecology

Occurs mainly in the dry tropical and northern arid zone regions of Australia between latitudes 17 degrees-24 degrees S. It extends from the Pilbara and Kimberley regions in Western Australia across Northern Territory to central and south-western Queensland and far north-eastern South Australia. Acacia elachantha has a scattered distribution throughout much of the Pilbara but it is not a conspicuous element within the landscape. It grows mainly on sandplains in more or less neutral (pH 6) deep red sand or sandy loam. It also occurs along creeks or drainage lines, and low rocky hills or lateritic plains in often skeletal, slightly acidic (pH 7.5) soil. It is often common in disturbed sites (e.g. road verges, borrow-pits) in the areas where it occurs. Further ecological information is given in Doran and Turnbull (1997 - where the species is referred to as A. cowleana) and McDonald and Maslin (1997).

Flowering and fruiting period

Flowering has been recorded from May to August with the main flush in July. Flowering is usually prolific. Pods with mature seeds occur from September to November.

Variation

A rare glabrous variant occurs in Pilbara and elsewhere across the range of the species (see McDonald and Maslin 1997 for discussion). The typical variant of the species is the more common and it comprises two forms (both of which occur in the Pilbara), one with golden hairy new shoots (hairs aging silvery) and the other with silvery hairy new shoots from initiation (no golden hair phase).

Affinities

Acacia elachantha is closely allied to, and until recently was confounded with, A. cowleana. Both species occur in the Pilbara but neither is especially common (although A. elachantha is the more widely distributed). Care needs to be taken not to confuse these two species: A. cowleana is recognized by its more robust growth habit, its new shoots being encrusted by many reddish brown resin when first initiated (best observed at x10 magnification or higher), often larger and coarser phyllodes, longer spikes with larger flowers and wider pods. Acacia elachantha is also related to A. colei and A. holosericea , and superficially resembles A. fecunda , all of which occur in the Pilbara (see these species for distinguishing features). Putative hybrids between A. elachantha and A. colei var. colei occur in Northern Territory (see McDonald and Maslin 1997).

Notes

Acacia elachantha is a fast growing, short-lived species (dies after about 5 years) that regenerates rapidly under natural conditions from the prolific quantities of seed that it produces from an early age.

Acacia elachantha is an attractive plant with horticultural potential for inland areas and in mine site rehabilitation; its main constraint, however, is that it is short-lived.

Although not known to be browsed, the phyllodes of this species appear to have good digestibility, high in protein with a good calcium to phosphorus ratio (Vercoe 1989).

Acacia elachantha has been 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 human food (see McDonald and Maslin 1997 for further information).

Further information on the utilisation and silviculture of A. elachantha (referred to as A. cowleana) is given in Doran and Turnbull (1997), and on aboriginal usage by Latz (1995).

Acacia elachantha is a tetraploid and is seemingly genetically invariate both within and between populations (see Moran et al. 1992 where the species is referred to as A. cowleana).

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is derived from the Greek elachys (little, small, short, low) and anthos (flower) and refers to the smaller flowers and shorter spikes which help distinguish the species from its closest relative, A. cowleana.

References

Doran, J.C. and Turnbull, J.W. (1997). Australian trees and shrubs: species for land rehabilitation and farm planting in the tropics. ACIAR Monograph No. 24. pp. 384. (Australian Centre for International Agricultural Research: Canberra.)

Latz, P.K. (1995). Bushfires and Bushtucker: Aboriginal plant use central Australia. pp. 400. (IAD Press: Alice Springs.)

McDonald, M.W. and Maslin, B.R. (1997). A reappraisal of Acacia cowleana and allied taxa, including the description of a new species, A. elachantha, from the tropical dry-zone of Australia. Australian Systematic Botany 10: 303-320.

Moran, G.F., Thomson, L., Grant, J. and Bell, C. (1992). Distribution of genetic variation within two dry-zone Acacia species and implications for their genetic improvement. pp. 74-81. In: A.P.N. House and C. Harwood (eds) Australian Dry-zone Acacias for Human Food. Proceedings of a workshop held at Glen Helen, Northern Territory, Australia, 7-10 August, 1991. pp. 151. (Australian Tree Seed Centre, CSIRO Division of Forestry: Canberra.)

Mueller, F. (1881). Plants of North-Western Australia. pp. 19. (Government Printer: Perth.)

Vercoe, T.K. (1989). Fodder value of selected Australian tree and shrub species. pp. 187-192. In: D.J. Boland (ed.) Trees for the tropics. Growing Australian multipurpose trees and shrubs in Developing Countries. pp. 247. ACIAR Monograph No. 10. (Australian Centre for International Agricultural Research: Canberra.)