Botanical name

Acacia holosericea Cunn. ex Don, Gen. Hist. 2: 407 (1832)

Common name

Candelabra Wattle and Silver Wattle

Description

Spindly, single-stemmed, openly branched shrubs 2-4 m tall (may become trees to 9 m outside the Pilbara), crowns sub-dense. Bark grey, smooth. Branchlets acutely angled for (10-) 20-30 cm below the apex, then becoming ąterete, usually sericeous with short, straight, closely appressed and silvery hairs (observed at x10 magnification or higher). New shoots usually silvery sericeous. Phyllodes obliquely narrowly elliptic, 10-20 (-25) cm long, 20-30 mm wide on Pilbara plants (but (1.5-) 2-5 (-6) cm elsewhere), mostly ascending to erect, straight (not shallowly recurved at apices), silvery dull green or sub-glaucous, usually sericeous with minute and closely appressed hairs (observed at x10 magnification or higher), asymmetrically narrowed at base; with normally 3 prominent longitudinal nerves 2 of which are basally confluent and sometimes contiguous with the lower margin of the phyllode, the minor veins forming a somewhat open, longitudinally orientated reticulum; narrowed at apex into a distinct, linear to triangular or asymmetrically ovate-elliptic, yellow apical point 1-3 mm long. Gland on upper margin of phyllode 0-2 mm above pulvinus, an additional smaller gland adjacent to the apical mucro on at least some phyllodes. Inflorescences rudimentary racemes with axes to 0.5 mm long; peduncles 3-7 mm long, ąappressed-hairy or glabrous; spikes 2-4 (-6) cm long, light golden, the flowers sub- densely arranged in the spikes (best observed in mature buds). Flowers 5-merous; sepals united; petals hairy (occasionally glabrous outside Pilbara). Pods tightly and often somewhat irregularly coiled, 2.5-4 mm wide, thinly crustaceous to coriaceous-crustaceous, ąglabrous, often remaining as entangled clumps on the plants following dehiscence. Seeds longitudinal in the pods, obloid-ellipsoid, 3-5 mm long, shiny, dark brown; aril bright yellow.

Characteristic features

Phyllodes large (mostly 10-20 cm x 20-30 mm wide on Pilbara plants), mostly ascending to erect, straight, with normally 3 prominent longitudinal nerves (2 confluent at base of phyllode), minor veins forming a somewhat open, longitudinally orientated reticulum, apical point 1-3 mm long and usually with a gland at its base. Inflorescences spicate, petals usually hairy. Pods tightly and often somewhat irregularly coiled, narrow, thin-textured, ąglabrous, often remaining as entangled clumps on the plants following dehiscence. Seeds dark brown, the aril bright yellow.

Distribution and ecology

Widespread in northern Australia where its main distribution extends from near Derby in Western Australia eastwards across the Kimberley region and Northern Territory to near Rockhampton in eastern Queensland. Scattered outliers occur in arid regions of the Pilbara (where it is known from only Hancock Gorge in the Hamersley Range and from near Nullagine), through central Northern Territory and in southwest Queensland. It grows in sometimes gravelly sand or loam; the Pilbara populations are confined to ephemeral watercourses. Further ecological details are provided by Doran and Turnbull (1997).

Flowering and fruiting period

Over its extensive geographic range this species flowers mainly from June to August, but flowering can occur at other times between April and October (Doran and Turnbull 1997). Pods with mature seeds have been collected (outside the Pilbara region) between August and October.

Variation

While the branchlets, new shoots, phyllodes and petals are hairy on Pilbara plants, they are sometimes glabrous elsewhere.

Taxonomy

In the past a number of arid zone/tropical Acacias with large, reticulately veined phyllodes, long spicate inflorescences and bright yellow seed arils had been confused with A. holosericea. However, following taxonomic reviews by Maslin and Thomson (1992) and McDonald and Maslin (1997) A. holosericea is now more narrowly defined and A. colei, A. cowleana, A. elachantha and A. neurocarpa are treated as distinct species. These species, except the last, occur in the Pilbara region. The small gland at the apex of many of the phyllodes (on the upper edge of phyllode at base to the apical point, best observed at x10 magnification or higher) is a good character for distinguishing A. holosericea from all its Pilbara relatives (gland not present in the relatives). However, the following combination of characters further serve to distinguish the species: branchlets acutely angled, new shoots silvery sericeous (not resin-coated or citron sericeous) when first initiated, phyllodes straight (not falcate throughout or curved at apex) with the minor nerves forming a distinct, open, longitudinally oriented reticulum, petals normally hairy and the pods tightly and often somewhat irregularly coiled.

Notes

Acacia holosericea is a fast-growing, short-lived species that has poor coppicing ability.

Information on its silvicultural characteristics, including growth rates under trial conditions, pests and diseases, and germination and establishment techniques, is summarized in Doran and Turnbull (1997).

The wood makes an excellent fuel as it has a moderately high density (550 kg/m³), splits easily, dries rapidly and has acceptable burning properties (Gough et al. 1989).

Unlike its relative A. colei, A. holosericea has limited potential for the production of human food (Thomson 1992).

The phyllodes, bark and pods are used indigenous peoples of the Northern Territory for pruritic skin conditions, headache and tropical infection (Aboriginal Communities of the Northern Territory 1993). These plants have also been used by traditional aborigines as a bush soap, fish poison and for making spear shafts (Brock 1998).

Conservation status

Although A. holosericea is uncommon in the Pilbara it is widespread elsewhere and is not considered rare or endangered.

Origin of name

The botanical name is derived from the Greek holos (entire, whole) and sericos (silky) and refers to the nature of the hairs that are found on many parts of most plants of this species.

References

Aboriginal Communities of the Northern Territory (1993). Traditional Aboriginal Medicines in the Northern Territory of Australia. pp. 651. (Conservation Commission of the Northern Territory of Australia: Darwin.)

Brock, J. (1988). Top end native plants: a comprehensive guide to the trees and shrubs of the top end of the Northern Territory. pp. 354. (John Brock: Winnellie, Darwin.)

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.)

Gough, D.K., Bell, R.E., Ryan, P.A. and Bragg, C.T. (1989). Drying and burning properties of the wood of some Australian tree species. pp. 177-186. In: D.J. Boland (ed.) Trees for the tropics. pp. 247. ACIAR Monograph No. 10. (Australian Centre for International Agricultural Research: Canberra.)

Maslin, B.R. and Thomson, L.A.J. (1992). Re-appraisal of the taxonomy of Acacia holosericea A. Cunn. ex Don, including the description of a new species, A. colei, and the reinstatement of A. neurocarpa A. Cunn. ex Hook. Australian Systematic Botany 5: 729-743.

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.

Thomson, L.A.J. (1992). Australia's subtropical dry-zone Acacia species with human food potential. pp. 3-36. In: A.P.N. House and C.E. 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. (CSIRO, Division of Forestry, Australian Tree Seed Centre: Canberra.)