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Botanical name

Common name

Aboriginal name

Description

Characteristic features

Distribution and ecology

Flowering and fruiting period

Variation

Affinities

Notes

Conservation status

Origin of name

References

Acacia trachycarpa

Botanical name

Acacia trachycarpa E. Pritzel, Bot. Jahrb. Syst. 35: 308 (1904)

Common name

Pilbara Minni Ritchi (preferred common name), Curly-bark Tree and Sweet-scented Minni Ritchi

Aboriginal name

Burduwayi, Purtuwari or Buruwaie (Yindjibarndi), Buruway or Purtuwari (Ngarluma) Yijaringu (Thalanyji), Parrhalyi or Parrkalyi (Nyangumarta) and Mundaru, Muntaru, Pudawarri, Putawarri, Putawayi or Butawarri (Kurrama)

Description

Resinous, obconic shrubs or small trees 1-5 m tall, crowns spreading and sometimes flat-topped, ultimate branchlets sometimes ±pendulous. Bark Minni Ritchi, burgundy red to red-brown and peeling off the stems in narrow strips which curl back on themselves to form scrolls down the stem. Branchlets glabrous or more commonly very sparsely appressed -hairy. New shoots slightly sticky at least when fresh, light green, with a mixture of silvery and light golden appressed hairs when young (but indumentum not conspicuous). Stipules persistent but not prominent, small (0.5-1 mm long) and brown. Phyllodes narrowly linear, 4-10 (-15) cm long and 0.8-2 mm wide in the typical variant but linear, narrowly oblong or oblong-oblanceolate, (15-) 20-40 mm long and a few reaching 3 (-5) mm wide in the dwarf variant, normally soft, delicate and not rigid (typical variant) or sometimes sub-rigid (dwarf variant), straight or shallowly curved or wavy, flat, sub-glabrous or more commonly with often sparse, appressed, silky hairs on nerves and margins, not shiny, green; parallel longitudinal nerves 3 or more per face but normally only the central nerve evident with the other nerves very obscure, the upper margin broader than the lower margin; apex narrowed to a fine, innocuous or ±pungent point. Gland situated on upper margin of phyllode 0-7 mm above pulvinus. Inflorescences simple; peduncles 5-15 mm long, glabrous or very sparsely appressed -hairy; spikes 9-20 (-30) mm long, golden. Flowers 5-merous; calyx dissected to 1/5-2/3 or more, golden-hairy. Pods narrowly oblong to linear, flat, scarcely raised over seeds, straight-sided to occasionally shallowly constricted between the seeds, (3-) 7-11 cm long, 7-12 mm wide, coriaceous, may persist on plants following dehiscence, moderately to strongly and often irregularly curved (sometimes into an open circle), resinous and sticky, finely reticulately nerved, sericeous with golden hairs when young but becoming glabrous or ±sparsely hairy with age (hairs wide-spreading to appressed and white), shiny, mid-brown. Seeds oblique in pods, 5-8 mm long, 4-7 mm wide, globose to obloid, depressed at centre, shiny, dark brown to black except dull yellow or brown at centre of seed; aril white.

Characteristic features

Resinous shrubs or small trees with spreading, sometimes flat-topped crowns. Bark Minni Ritchi, red-brown. Stipules persistent, small (0.5-1 mm long) and brown. Phyllodes usually narrowly linear, soft, delicate and not rigid, green, longitudinally multi-nerved but normally only the central nerve evident, upper margin slightly thickened and broader than the lower margin. Spikes golden. Pods flat, moderately to strongly and often irregularly curved (sometimes into an open circle), resinous and sticky, golden hairy when young, finely reticulately nerved. Seeds dark brown to black except dull yellow or brown at centre. Normally found along watercourses.

Distribution and ecology

Mostly confined to the Pilbara region of northwest Western Australia where it is widespread and common, usually along creeks and rivers mostly to the north and west of the Hamersley Range; an outlier occurs in the Kimberley region. In the Pilbara A. trachycarpa is often common in the places where it occurs sometime forming thickets on coastal pindan sandplains. It often grows with A. pyrifolia and/or A. coriacea subsp. pendens on alluvial river plains and washes. An uncommon variant occurs on drier sites away from watercourses.

Flowering and fruiting period

Flowers from April to August and sometimes October with the main flush from May to July. Pods with mature seeds have been collected from September to December with most in October.

Variation

Acacia trachycarpa is a variable species with two forms recognized. Typically it is a spreading, obconic tree or shrub about 2-5 m tall with phyllodes mostly 4-10 cm long, 1-2 mm wide and not rigid; these plants are normally found along rivers and creeks. A relatively uncommon variant occurs scattered throughout the range of the species away from water courses, including coastal dunes on Finucane Island, gravelly, spinifex plains near Nullagine and on rocky ranges (e.g. the Barlee Range Nature Reserve to the south of the Pilbara). It is a low spreading shrub to about 1 m tall with short phyllodes (15-) 20-40 mm long with some occasionally wider than normal (3-5 mm) that tend to be held more erect and sometimes more rigid than the typical variant. Despite the above differences current evidence suggests that the dwarf variant is not worthy of formal rank.

Affinities

Acacia trachycarpa is most closely allied to Minni Ritchi species that occur in northern Australia, namely, A. chisholmii, A. gracillima and A. lysiphloia, but it also has affinities with the Pilbara Minni Ritchi species A. effusa (which has much smaller, differently shaped phyllodes) and A. monticola (which has shorter, broader phyllodes and normally round or oblong heads). In the Pilbara A. trachycarpa hybridizes with A. tumida (see A. trachycarpa x tumida var. pilbarensis) and rarely with A. eriopoda (see A. eriopoda x trachycarpa) and A. monticola (see A. monticola x trachycarpa); see also A. sp. Nullagine (B.R. Maslin 4955). A rare possible hybrid between A. trachycarpa and A. stellaticeps is recorded from near Roebourne but as we were not able to relocate this entity it's taxonomic status remains ambiguous. Plants described by Maslin (1983) as A. ancistrocarpa x trachycarpa are now referable to A. trachycarpa x tumida var. pilbarensis.

Notes

A reasonably fast growing species that is reported to be frost sensitive and not very drought tolerant. Plants are killed by intense fires but have the ability to resprout after cool fires or mechanical clearing.

It is used in amenity plantings in places in the Pilbara (e.g. Karratha) and has also been introduced into West Africa for firewood and stock fodder (where it was found to be palatable to sheep, cattle and goats). Under trial conditions in Malawi A. trachycarpa produced 3.3 t/ha of foliage after 2.2 years. Although the phyllodes may contain low levels of cyanogenic glycoside the species is unlikely to be dangerous to stock (Maslin et al. 1987). In Niger this species has been used successfully as a low windbreak.

The air-dry density of the wood is 770 kg/m3 with a calorific value of 4740 kcal/kg.

Indigenous people in the west and central Pilbara boiled young leaves to make a sticky liquid for the treatment of skin irritations. The wood was used to make spears, fighting sticks and digging tools. The smoke from burnt phyllodes was also used to calm troublesome children. Plants of A. trachycarpa are frequently infected with a spherical gall with rather long, narrow projections (reminiscent of the fruits of Liquidambar).

Further information on the utilisation and silviculture of this species are given in Turnbull (1986) and Doran and Turnbull (1997).

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is derived from the Greek trachys (rough) and carpos (fruit) and refers to the rough-textured pods. As discussed under A. monticola some past confusion has existed with respect to common names between this species and A. trachycarpa.

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.)

Maslin, B.R. (1983). Studies in the genus Acacia (Leguminosae: Mimosoideae) - 14. New taxa from north-west Western Australia. Nuytsia 4(3): 383-410.

Maslin, B.R., Conn, E.E. and Dunn, J.E. (1987). Cyanogenic Australian species of Acacia: a preliminary account of their toxicity potential. pp. 107-111. In: J.W. Turnbull (ed.) Australian Acacias in developing countries. Proceedings of an international workshop held at the Forestry Training Centre, Gympie, Australia, 4-7 August 1986. ACIAR Proceedings No. 16. pp. 196. (Australian Centre for International Agricultural Research: Canberra.)

Turnbull, J.W. (ed.) (1986). Multipurpose Australian trees and shrubs: lesser-known species for fuelwood and agroforestry. pp. 316. (Australian Centre for International Agricultural Research: Canberra.)

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