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Botanical name

Common name

Aboriginal name

Description

Characteristic features

Distribution and ecology

Flowering and fruiting period

Variation

Taxonomy

Affinities

Notes

Conservation status

Origin of name

References

Acacia sclerosperma subsp. sclerosperma

Botanical name

Acacia sclerosperma F. Muell. subsp. sclerosperma, S. Sci. Rec. 2(7): 150 (1882)

Common name

Limestone Wattle (preferred common name), Silver Bark Wattle and Rattle Tree

Aboriginal name

Bagurda (Banyjima), Bagurda, Bugurda, Bugguda, Pakuta or Pakurta (Kurrama), Purtarrpa (Nyangumarta) and Warntayin (Kariyarra)

Description

Dense, rounded or sometimes obconic, multi-stemmed, glabrous shrubs or small trees (1-) 2-4 (-6) m tall and spreading to 4-6 m across. Bark dark grey and fissured towards base of oldest stems, otherwise smooth and light grey on branches and branchlets. New shoots light green. Phyllodes linear, terete to flat, (5-) 6-14 (-17) cm long, (0.5-) 1-4 (-5) mm wide, ±thick and fleshy, smooth (but often longitudinally ±wrinkled when dry), green to grey-green or sub-glaucous; with 4 longitudinal nerves (1-nerved per face when flat); apex often with tip recurved. Glands not prominent, 2 or 3 along the upper margin of the phyllode, the lowermost 1-22 mm above the pulvinus, a smaller (often obscure) gland adjacent to the apical mucro. Inflorescences 2-5-headed racemes which are 3-30 mm long, occasionally growing out at apex; peduncles (4-) 6-15 (-20) mm long; heads globular, 9-11 mm in diameter when fresh, golden, sub- densely 15-20-flowered. Flowers 5-merous; buds bright green; calyx truncate. Pods conspicuous on plants, pendulous, moniliform to sub-moniliform, breaking readily breaking at constrictions between seeds, large, (6-) 9-14 (-16) cm long and 8-20 mm wide, woody, dehiscing first by opening from the apex, yellow-brown, often pruinose when young. Seeds longitudinal in pods, ±globose, large (7-10 mm long), turgid, rattling in unopened pods at maturity, ±shiny, dark brown to black, seed coat thick and hard; aril small, hemispherical to depressed-clavate, red.

Characteristic features

Spreading, glabrous shrubs or small trees. Bark on branches and branchlets light grey. Phyllodes long and narrow (mostly 6-14 cm x 1-4 mm wide), ±fleshy, smooth (when fresh), with 4 fine longitudinal nerves (1-nerved per face when flat); gland (often obscure) adjacent to the small apical point. Inflorescences rather short racemes (3-30 mm); heads sub- densely flowered, golden; buds bright green. Pods large (mostly 9-14 cm x 8-20 mm) and moniliform to sub-moniliform, breaking readily breaking at constrictions between seeds, woody. Seeds large (7-10 mm long) with a very hard seed coat and a small red aril.

Distribution and ecology

Confined to Western Australia where it extends from the Pilbara and Murchison regions south to near Mingenew and Mt Magnet, with disjunct occurrences near Lake Carnegie and Wongan Hills. It is widespread in the Pilbara where it grows on coastal dunes and more typically along inland creeks and flood plains, on calcrete or in alkaline sand, loam or clay. Also occurs on Thevenard and Airlie Islands off Onslow but is apparently not common there. A variant of subsp. sclerosperma with thinly textured phyllodes and a sucker habit also occurs on these islands.

Flowering and fruiting period

According to Mitchell and Wilcox (1994) A. sclerosperma flowers opportunistically after rain. Pilbara plants have been recorded as flowering from May to August with the main flush seemingly in June and July. Pods with mature seeds have been collected between August and December, with most occurring in October.

Variation

Phyllodes vary from terete to flat. Two variants with thinly textured phyllodes and a sucker habit occur on Thevenard and Airlie Islands off Onslow, together with the typical variant of the species, see Maslin 2007. Additionally, these two island variants can normally be recognized by their phyllode dimensions: in typical subsp. sclerosperma the phyllodes are (5-) 7-9 cm long, 1.2-2 mm wide with l:w = 30-50; in subsp. sclerosperma (island variant 1) the phyllodes are 6-9 (-11) cm long, 3-5  mm wide with l: w = (8-) 15-30 (-40); in subsp. sclerosperma (island variant 2) the phyllodes are 4-7 cm long, 2-4 mm wide with l:w = (9-) 15-30.

Taxonomy

Acacia sclerosperma comprises two subspecies, subsp. sclerosperma and subsp. glaucescens (which does not occur in the Pilbara).

Affinities

Acacia sclerosperma belongs to a group of related species called the A. bivenosa group (see Chapman and Maslin 1992 for discussion). Other members of this group which occur the Pilbara include A. ampliceps, A. bivenosa and A. ligulata. Acacia sclerosperma is distinguished from all these relatives by having large, woody pods and large seeds. The pods are similar to those of the unrelated A. stenophylla which can be recognized by having wider phyllodes with many fine parallel nerves (observe at x10 magnification), seeds with scarcely arillate funicles and pale-coloured flower-heads. Within the Pilbara this subspecies hybridizes with A. ampliceps and A. bivenosa in a few places (see A. ampliceps x sclerosperma subsp. sclerosperma and A. bivenosa x sclerosperma subsp. sclerosperma); hybrids with A. ligulata are recorded for a few localities outside the Pilbara (see Chapman and Maslin 2001).

Notes

A somewhat salt tolerant species that is useful as a windbreak in coast areas. When grown in gardens at least (e.g. in Newman) it coppices vigorously when cut at about 0.5 m above ground level (Ken Walker, pers. comm.).

Not highly palatable to stock and eaten only as a forage of last resort; crude protein content is about 8% and digestibility 45% (Mitchell and Wilcox 1994). These authors also report that in the Ashburton district A. sclerosperma is sometimes an increaser species on floodplain and limestone areas if palatable perennial grass and shrub species are overgrazed.

Indigenous people from the central Pilbara used the bark from Limestone Wattle to tan animal hides and as a dye.

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is taken from the Greek scleros (hard) and sperma (seed).

References

Chapman, A.R. and Maslin, B.R. (1992). Acacia Miscellany 5. A review of the A. bivenosa group (Leguminosae: Mimosoideae: Section Phyllodineae). Nuytsia 8(2): 249-283.

Chapman, A.R. and Maslin, B.R. (2001). Acacia descriptions. In: A.E. Orchard and A.J.G. Wilson (eds) Flora of Australia. Volume 11A. pp. 536. (ABRS/CSIRO Publishing: Australia.)

Maslin, B.R. (2007). The Acacia bivenosa group of Wattles on Airlie & Thevenard Islands, Pilbara region, W.A. Unpublished Report produced for Apache Energy and Cheveron Australia. pp. 36. (Department of Environment and Conservation: Perth.)

Mitchell, A.A. and Wilcox, D.G. (1994). Arid shrubland plants of Western Australia. Edn. 2. pp. 478. (University of Western Australia Press in association with the Department of Agriculture: Perth.)

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