418 
Telopea 9(2): 2001 
Other specimens examined: New South Wales: North Western Slopes: Myall Creek Station: W. 
Halves, P. O'Keefe & J. Keivley NSW445999M46002, 17 July 2000 (NSW); F. Millar NSW441449, 25 May 
2000 (BRI, NSW, PERTH); K. Stevens NSW443828, 23 Feb 2000 (NSW); T. Tame 6285, 4 Nov 2000 (BRI, 
CANB, Hunter Region Botanic Gardens, MEL, NE, NSW, PERTH). 
Discussion 
Acacia atrox is distinguished by the markedly splayed or dilated base of its phyllodes. 
It does not appear to have any particularly close relatives, but may have some 
affinities with A. carneorum Maiden from central-eastern South Australia and the 
North and South Far Western Plains of New South Wales, which is superficially 
similar in its gregarious suckering habit, rigid, pungent phyllodes, globular flower- 
heads and united sepals. Acacia carneorum appears to produce few fruits, which may 
also be the case for A. atrox where pods have not been observed. Acacia carneorum 
mainly differs from A. atrox by not having splayed phyllode bases, and by having 
often thicker, 4-veined phyllodes (distinctly quadrangular in section), hairy branchlets 
and phyllodes (especially when young), simple inflorescences and yellow to bright 
yellow flower-heads. 
The phyllodes of Acacia colletioides Benth. (which occurs in Western Australia, South 
Australia, New South Wales and Victoria) are superficially similar to those of A. atrox, 
however, they are strongly 8-veined, have raised stomata, are not splayed at the base 
and are inserted on distinct raised stem-projections; also the sepals are free in 
A. colletioides. Acacia pickardii Tindale (restricted in north-eastern South Australia and 
south-eastern Northern Territory) is superfically similar to A. atrox in that it has 
pungent phyllodes, spreads by suckering, produces hakea fruit-like galls in some 
phyllodes and appears to rarely produce fruit, but differs most obviously by the 
phyllodes being ± erect, terete and obscurely 4-veined, the stipules conspicuously 
spinose, the inflorescences simple and the sepals free. Acacia pachypoda Maslin from 
Western Australia is superficially similar to A. atrox, especially because it also has 
pungent phyllodes with prominently dilated bases, however, the relationship between 
these two species is not close. Acacia pachypoda is a small shrub which differs 
significantly in having its short racemes subtended by conspicuous imbricate bracts 
which enclose the young heads, no bracteoles subtending the flowers, shorter 
peduncles, shorter phyllodes, and more. In the absence of A. atrox pods and 
biochemical or genetic (DNA) studies it is difficult to further assess possible 
relationships of this unusual species. 
Hawes et al. (2000) estimated a population of 50 000-100 000 individual plants 
(or more correctly, stems, if clonal) of A. atrox in an area of approximately 10 ha., and 
T. Tame (pers. comm.) estimated 20 000 plants in an area of approximately 2 ha. 
However, many of the plants, if not the whole population, could be clonal since 
younger plants appear to be suckering from existing roots and the plants are 
morphologically very uniform (Hawes et al. 2000; T. Tame, pers. comm.). According to 
Hawes et al. (2000), vegetative reproduction and apparent poor seed production in this 
species is also indicated by the absence of any individuals further down the local 
catchment. 
There is a history of habitat disturbance, including the 'thinning' of vegetation, 
grazing (cattle until very recently), pasture improvement (most recently 2 years ago) 
and stick raking (4 years ago) (Hawes et al. 2000). These activities may well have 
promoted the apparent expansion of A. atrox in recent years through disturbance of 
the soil and surface roots stimulating extensive suckering (Hawes et al. 2000). There is 
the possibility that the area might be burned with the aim of controlling the spread 
