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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 bivenosa

Botanical name

Acacia bivenosa DC., Prodr. 2: 452 (1825)

Common name

Two-Veined Wattle and Hill Umbrella Bush

Aboriginal name

Murrurpa, Murruba, Murrurbaor and Morama (Kurrama), Mururru (Banyjima) and Mururr (Nyangumarta)

Description

Rounded or obconic shrubs normally 1-2.5 m tall and spreading to about 3 m across, rarely prostrate, crowns either bushy or openly branched, sparingly or much-branched at base, sometimes to 3-4 m tall with a spindly, open, habit, single-stemmed or sparingly divided at base and pendulous to sub-pendulous branchlets. Bark light to mid-grey, smooth. Branchlets usually glabrous, often slightly pruinose. New shoots bright green. Phyllodes variable, narrowly elliptic to oblong-elliptic or obovate to oblanceolate, 2-5.5 (-7) cm long, 6-20 (-27) mm wide, length: width = 2-5 (-7), not rigid, smooth, commonly sub-fleshy and snapping cleanly when bent when fresh, finely wrinkled when dry, glabrous, glaucous to sub-glaucous , infrequently green (except on new growth); usually 2-nerved (nerves of equal prominence or sometimes the central one more pronounced than the other), infrequently 1-nerved (most commonly seen in the wispy variant); apex obtuse or sometimes acute, mucro straight to incurved. Glands commonly 2 or 3 along upper margin of phyllode, the lowermost prominent and 1-12 mm above pulvinus, additional smaller gland commonly at base of apical mucro. Inflorescences mostly short racemes with the axes growing out at apex and the subsequent inflorescences simple (not racemose) within axil of phyllodes; peduncles (10-) 15-35 (-45) mm long, glabrous; heads globular, about 10 mm diameter at anthesis, rich golden, sub- densely 16-23 (-32)-flowered. Flowers 5-merous; calyx ±truncate; buds bright green. Pods sub-moniliform but constrictions not pronounced, readily breaking into one-seeded or few-seeded segments at the constrictions, 2-10 cm long, 5-8 (-9) mm wide, ±erect, crustaceous to sub-woody, opening elastically from apex with the valves recurved following dehiscence, straight to shallowly curved, glabrous, yellowish brown to light brown. Seeds longitudinal in pods, remaining in pods after dehiscence, obloid-ellipsoid, 4-6 mm long, 2.5-4 mm wide, glossy, dark brown to black; aril red (tinged orange, sometimes completely orange outside the Pilbara).

Characteristic features

Glabrous, small shrubs (rarely prostrate) or sometimes tall with an open spindly growth form and pendulous to sub-pendulous branchlets. Bark smooth and grey. Phyllodes variable, narrowly elliptic to oblong-elliptic or obovate to oblanceolate, relatively short and broad (mostly 2-5.5 cm x 6-20 mm), normally 2-nerved, ±fleshy (finely wrinkled when dry), normally glaucous to sub-glaucous (new growth bright green). Gland situated at apex of phyllode, at base of apical point. Inflorescences both simple and racemose; peduncles long (mostly 15-35 mm); heads rich golden; buds bright green. Pods ±sub-moniliform and erect, hard-textured (crustaceous to sub-woody), readily breaking at constrictions between seeds. Seeds often remaining in pods after dehiscence, aril red.

Distribution and ecology

Widespread in the arid zone of W.A., N.T. and western Qld, north of about 25 degrees S. Widespread in the Pilbara and often common in the places where it occurs; it also grows on a number of the islands off the Pilbara coast, including Airlie Island. Grows in a variety of soils and habitats, including coastal dunes, stony open plains, rocky hillsides and gullies low in the landscape but has a preference for calcareous and other alkaline soils. It is commonly found along (rocky) watercourses, often with A. trachycarpa and/or A. pyrifolia. It grows in shrubland and open woodland, often with a ground cover of hard spinifex (Triodia wiseana).

Flowering and fruiting period

Flowers from May to October with the main flowering flush in July and August. Mature pods have been collected between September and December, with most in October.

Variation

Acacia bivenosa is an extremely variable species, especially with respect to growth form and phyllode morphology. A brief discussion of variation within Pilbara plants is presented below but a full discussion of variation within the species over its extensive geographic range is given in Chapman and Maslin (1992). A very unusual plant from Balfour Downs Station had hairy branchlets (hairs short, straight and wide-spreading); it grew with the normal glabrous form of A. bivenosa.

An attractive, spindly variant with an open wispy crown (branches commonly sub-pendulous or pendulous) occurs on many calcrete outcrops and other basic soils throughout the Hamersley Range and on coastal sands and dolerite hills around Dampier. It appears to differ from the normal shrubby form of the species mainly in its habit (the two forms appear to intergrade in places), although there is a tendency for the spindly form to have slightly more elongate phyllodes than the shrubby, typical form, and the phyllodes are sometimes 1-nerved.

The phyllodes of A. bivenosa are typically 2-nerved; these nerves are often of equal prominence but sometimes the central one is more pronounced than the other and this second nerve is sometimes very obscure. However, occasionally the phyllodes are 1-nerved and this is most commonly seen in the wispy variant referred to above. Some plants possess both 1- and 2-nerved phyllodes. As discussed elsewhere (Maslin 1982) the phyllodes on plants from the Hamersley Range are often slightly more elongate (i.e. higher l:w ratio) than those found on plants elsewhere. The sympatric occurrence of plants with green phyllodes and those with glaucous phyllodes is not unusual and has no taxonomic significance. The inflorescences of A. bivenosa comprise a mixture of racemes and simple axillary heads and both type are commonly found on many specimens (see Chapman and Maslin 1992 for discussion).

Affinities

Acacia bivenosa has three close relatives in the Pilbara, A. ampliceps , A. ligulata and A. sclerosperma subsp. sclerosperma but is distinguished by its short, broad, usually 2-nerved phyllodes and long peduncles which are often axillary within axil of phyllodes (racemes are often present on the plants as well). Within the Pilbara region A. bivenosa sometimes hybridizes with A. ampliceps and A. sclerosperma.

Notes

Acacia bivenosa is generally killed by fire and regenerates from seed although under very cool burn conditions large plants may regenerate from root stock close to the base of the parent plant. Fresh seeds require pre-treatment to achieve germination which can approach 100% (Fox and Dunlop 1983).

In the Pilbara A. bivenosa is used extensively in the land rehabilitation industry as it is a primary colonizer.

This species can be heavily grazed by livestock, especially at the seedling stage.

Indigenous people also obtained edible grubs from the roots.

On the Dampier Peninsula, Kimberley, the immature pods of this species attract flocks of Red-winged parrots which extract the seeds (Kenneally et al. 1996).

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is derived from the Latin bi- (two) and venosus (veined), referring to the usually 2-veined phyllodes.

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.

Fox, J.E.D. and Dunlop, J.N. (1983). Acacia species of the Hamersley Ranges, Pilbara Region of Western Australia. Mulga Research Centre. Occasional Report No. 3. pp. 94. (Western Australian Institute of Technology: Bentley.)

Kenneally, K.F., Edinger, D.C. and Willing, T. (1996). Broome and beyond: Plants and people of the Dampier Peninsula, Kimberley, Western Australia. pp. 256. (Department of Conservation and Land Management: Western Australia.)

Maslin, B.R. (1982). Studies in the genus Acacia (Leguminosae: Mimosoideae) - 11. Acacia species of the Hamersley Range area, Western Australia. Nuytsia 4(1): 61-103.

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