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Botanical name
Acacia aneura F. Muell. ex Benth., Linnaea 26: 627 (1855)
Common name
Mulga
Aboriginal name
Wirndamarra (Ngarluma, Yindjibarndi and Banyjima), Wintamarra, Windamarra, Tharrgan, Tharrkan or Wintamaya (Kurrama), Wintamarra or Wirntamarra (Nyamal), Wirntamarra (Kariyarra, Putijarra and Nyangumarta), Munturru (Putijarra), Kujilara (Jiwarli), Kurnturr (Martuthunira), Warlun (Thalanyji) and Karnturr (Martuthunira)
Description
Shrubs or trees (2-) 3-10 (-12) m tall, young plants often with a pseudo-conifer growth form. Bark grey, finely or coarsely fissured towards base of trunks, otherwise smooth. Branchlets not pendulous, terete, ribless or (often obscurely) ribbed at extremities, the ribs sometimes slightly resinous, normally sparsely to moderately silvery sericeous between the ribs (the hairs minute, straight and appressed: difficult to see without magnification), becoming glabrous with age. New shoots resinous, not sticky (at least when dry), light brown to dark brown or red-brown at initiation due to dense layer of microscopic resin hairlets which become sparse and are eventually lost as shoot matures. Phyllodes single or (mostly on juvenile plants) clustered in groups of 2-4 per node, (2-) 4-10 (-13) cm long, 1-4 mm wide, terete to flat and linear or rarely linear-elliptic, ascending to erect, not rigid, ±straight to incurved (very rarely recurved) or shallowly wavy, green to grey-green or sub-glaucous (rarely glaucous), obscurely appressed-hairy especially between the nerves, sometimes glabrous; parallel longitudinal nerves numerous, fine, of uniform prominence, close together, resinous (resin most evident on young phyllodes); apices acute, straight to sub-uncinate or occasionally uncinate, not spiny; discrete marginal nerve absent or very rarely poorly developed. Gland situated on upper margin of phyllode 0-4 (-10) mm above the pulvinus. Inflorescences simple; peduncles (2-) 3-15 mm long, glabrous or sparsely appressed-hairy, the hairs silvery and often interspersed with ±scattered red-brown resin hairlets; spikes 10-35 mm long. Flowers 5-merous; sepals free, linear-spathulate. Pods oblong to narrowly oblong or oblong-elliptic, (10-) 15-70 mm long, 5-22 mm wide, flat, papery, straight, light brown or yellow-brown to dark brown or greyish brown, nerveless to obscurely longitudinally or transversely nerved, glabrous to moderately sericeous (the hairs difficult to see without magnification); marginal wing absent or if present narrowed (to 1 mm wide). Seeds longitudinal to transverse in the pods, obloid to ellipsoid or ±ovoid, 4-6 mm long, 3-4 mm wide, dark brown, shiny; aril small, creamy white.
Distribution and ecology
Mulga is widespread and common in arid Australia. In the Pilbara, it occurs mostly from the Fortescue River and southern Chichester Range southwards with the West Angelas area containing the greatest diversity of forms. Mulga favours heavy-textured soil along alluvial flats and water courses. It often forms dense stands in shrubland and woodland settings. On Bajada plains (convergence of neighbouring alluvial fans) these dense Mulga stands may alternate with bare hardplains areas. This type of patterning, which usually occurs along the contour is called Grove-intergrove Mulga, Tiger bush or Banded Mulga and is particularly common on the Bajada plain at the front of the Hamersley Range above the Fortescue River and on the large alluvial flats such as Coondewanna and Wanna Munna Flats on the Hamersley Plateau. Such Mulga communities tend to be very susceptible to minor changes in surface hydrology and the flow of nutrients into and out of the woodlands. In more steeply sloping situation, particularly areas covered by a surface strew of cobbles and rocks at the bases of banded ironstone ranges and ridges and above the Bajada plain, extensive Mulga woodlands or shrublands may occur over an understorey of spinifex. This community type is common on the central and southern extent of the Hamersley Plateau, particularly in the West Angelas, Angelo River and Giles Minni areas. On the southern slopes of the Hamersley Plateau abutting the hardpan plains of the Ashburton River catchment Mulga woodland and shrubland may extend across the landscape sequence from the top of the highest ridges down to the creekline draining the valley floor (van Leeuwen and Fox 1985). Environmental variables, particularly access to soil water have been suggested (Fox and van Leeuwen 1985, Gerald Page pers. comm.) to significantly influence the distribution of Mulga across the landscape and may explain why the largest individuals and densest woodland tend to occupy water gaining sites low in the landscape. The preponderance of large trees (up to 12m) on southern shaded slopes (East Munjina Gorge) also substantiates this relationship between soil water availability and size of Mulga.
Many of the Mulga communities tend to be extremely vulnerable to fire with most Mulga plants succumbing to even the coolest of burns. The usual mode of regeneration is from seed (Fox 1980); however, some varieties do resprout advantageously from the stem or main trunk while others which have only been lightly scorched may recover by regrowing new phyllodes. In instances where the bole of the trunk is burnt some varieties may regenerate from root sprouts. Seed germination in Mulga is significantly enhanced by pre-treating (boiling water) and tends to be best at temperatures approaching 20º C (Fox and Dunlop 1983). A best temperature for germination of 20º C contracts notably with most other Pilbara wattles tested where the temperature approached 25º C. This discrepancy supports the suggestion that Mulga is at the limits of it bioclimatic range in the Pilbara and is typically a species of the cooler southern arid zone (Beard 1975).
Flowering and fruiting period
Mulga flowering and fruiting is most likely determined by the timing and intensity of rainfall events. Plants can flower from March to May (following summer rains) and also in June and July (following winter rains). Pods with mature seeds occur from September through to early November.
Taxonomy
Acacia aneura and related species form a very complex and polymorphic assemblage of taxa with A. aneura itself the most variable (see Miller et al. 2002 for discussion). These species are currently under review therefore the classification here of Pilbara entities within A. aneura is provisional. Currently 10 varieties are recognized within A. aneura (Pedley 2001) of which six appear to occur in the Pilbara, namely, var. conifera, var. intermedia, var. macrocarpa, var. microcarpa, var. pilbarana and var. tenuis. These varieties encompass most of the variation in Mulga in the Pilbara and are the entities upon which this Wattles of the Pilbara treatment of Mulga is based. It is often difficult to distinguish between the varieties, and between A. aneura and related species (especially A. ayersiana and A. paraneura) on account of seemingly intermediate forms. Judging from the maps provided in the Flora of Australia treatment of A. aneura Pedley (2001) did not record var. conifera, var. macrocarpa or var. microcarpa for the Pilbara. He did however cite a specimen identified as A. aneura var. aneura from the region (we now regard this specimen to be A. aneura var. pilbarana) and doubtfully referred some Hamersley Range specimens to var. major (we regard these specimens as belonging to an intergrade between A. aneura var. intermedia and A. ayersiana).
In past literature it is often not possible to know to which of the varieties the information applies. Therefore, the Wattles of the Pilbara data for A. aneura is derived mainly from a compilation of our field and herbarium studies and applies only to Pilbara plants.
Affinities
Acacia aneura is closely related to A. ayersiana (phyllodes and pods broad), A. affin. clelandii (generally larger and more thickly textured pods, larger seeds and shorter flowering spikes), A. minyura (phyllodes small, branchlets prominently resin-ribbed) and A. paraneura (trees with sparse crowns and often weeping branchlets). In the Pilbara A. aneura may superficially resemble A. exilis , A. balsamea and A. sibirica , and may possibly be confused with these species in the absence of flowers or pods.
Notes
Mulga is not only a very important component of arid zone natural ecosystems but also provides many commodities for man. Mulga species are commonly used in minesite rehabilitation projects in the Hamersley Range. They also form a significant part of the dry-range diet of sheep in arid Australia, but without supplementary high quality feed it is barely sufficient for subsistence. Further information on the fodder value of Mulga is given in Everist (1949, 1969), Chippendale and Jephcott (1963), Askew and Mitchell (1978), Cunningham et al. (1981), Goodchild and McMeniman (1987), Mitchell and Wilcox (1994) and Doran and Turnbull (1997).
Ngarluma, Banyjima, Yindjibarndi and Kurruma people of the Pilbara use A. aneura in various ways. The hard, dense wood of mature plants is used to make wanu or warnu (women's fighting sticks), kurartu (digging sticks), mirru or wulparra (spearthrowers), jurnha (clubs), gurrardu (walking sticks) and jurna (tapping sticks), while wood from young plants is used to make marrandu (spears) and ceremonial head adornments. Edible Mulga Apple, a fruit-like structure (jagarlurlu, jakatutu, jagadurdu) which is actually a wasp gall, was obtained from some Mulga plants. Wintamarra is also the main tree for building bough shelters (Young 2007). Mulga seed (purtuwari or jalyka) is also roasted on an open fire and eaten.
Conservation status
Not considered rare or endangered.
Origin of name
The species name comes from the Greek words a (not) and neuron (a nerve) in allusion to the absence of conspicuous veins on the phyllodes.
References
Askew, K. and Mitchell, A.S. (1978). The fodder trees and shrubs of the Northern Territory. Extension bulletin No. 16. pp. 84. (CSIRO Division of Primary Industry: Alice Springs.)
Beard, J.S. (1975). Vegetation survey of Western Australia - Pilbara. (University of Western Australia Press: Nedlands.)
Chippendale, G.M. and Jephcott, B.R. (1963). Topfeed. The fodder trees and shrubs of Central Australia. Extension article No. 5. pp. 51. (Northern Territory Administration, Animal Industry Branch: Alice Springs.)
Cunningham, G.M., Mulham, W.E., Miltnorpe, P.L. and Leigh, J.H. (1981). Plants of western New South Wales. pp. 766. (Government Printing Office: Sydney.)
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.)
Everist, S.L. (1949). Mulga (Acacia aneura F. Muell) in Queensland. Queensland Journal of Agricultural Science 6: 87-131.
Everist, S.L. (1969). Use of fodder trees and shrubs. Advisory leaflet No. 1024. pp. 44. (Queensland Department of Primary Industries, Division of Plant Industry: Brisbane.)
Fox, J.E.D. (1980). Effects of Fire on the Mulga. pp. 1-19. Mulga Research Centre. Annual Report No. 3. (Western Australian Institute of Technology: Bentley.)
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.)
Fox, J.E.D. and van Leeuwen, S.J. (1985). Observations on germination and early development of several Pilbara species in relation to environmental variables. Mulga Research Centre Journal 8: 93-100.
Goodchild, A.V. and McMeniman, N.P. (1987). Nutritive value of Acacia foliage and pods for animal feeding. pp. 118-122. In: J.W. Turnbull (eds) 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.)
Miller, J.T., Andrew, R.A. and Maslin, B.R. (2002). Towards an understanding of variation in the Mulga complex (Acacia aneura and relatives). Conservation Science Western Australia 4(3): 19-35.
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.)
Pedley, L. (2001). Acacia aneura. pp. 314-322. In: A.E. Orchard and A.J.G. Wilson (eds) Flora of Australia. Volume 11B. pp. 536. (ABRS/CSIRO Publishing: Australia.)
van Leeuwen, S.J. and Fox, J.E.D. (1985). An account of edaphic factors in relation to the distribution of perennial woody species in a tropical Mulga community. Mulga Research Centre Journal 8: 1-12.
Young, L. (2007). Lola Young: Medicine Woman and Teacher. Complied by Anna Vitenbergs. pp. 160. (Fremantle Arts Centre Press: Fremantle.)