Acacia macdonnelliensis, commonly known as MacDonnell mulga or Hill mulga, is a species of flowering plant in the family Fabaceae and is endemic to central Australia. The Alyawarr people know the plant as , the Kaytetye know it as or and the Western Arrernte people know it as . It is a shrub or tree with deeply fissured grey bark, erect, very narrowly elliptic to linear or thread-like phyllodes, dense spikes of golden yellow flowers, and linear, papery pods slightly constricted between the seeds.
Description Acacia macdonnelliensis is shrub or tree that typically grows to a height of and one or several trunks with deeply fissured grey bark and branchlets sometimes covered with a few hairs, otherwise glabrous. Its phyllodes are erect, very narrowly elliptic to linear or thread-like, straight to slightly sickle-shaped, long, wide and leathery, with a hook-like tip. The flowers are golden yellow, densely arranged in spikes mostly long and in diameter on peduncles long. Flowering time depends on subspecies, and the pods are linear, long, wide, papery, pale brown and slightly constricted between the seeds. The seeds are long and dark brown with a whitish aril.
Taxonomy Acacia macdonnelliensis was first formally described in 1978 by John Richard Maconochie in the Journal of the Adelaide Botanic Garden from specimens he found in Serpentine Gorge in 1967.
In 1987, Bruce Maslin described two subspecies of A. macdonnelliensis in the journal Nuytsia, and the names are accepted by the Australian Plant Census: Acacia macdonnelliensis subsp. macdonnelliensis has flat phyllodes, the racemes long and flowers from April to September. Acacia macdonnelliensis subsp. teretifolia Maslin has terete phyllodes, the racemes mostly long and flowers from June to August.
Distribution and habitat Acacia macdonelliensis is found in southern parts of the Northern Territory around Alice Springs and in far eastern Pilbara and north eastern Goldfields regions of Western Australia. It grows in areas of sandstone and quartzite along rocky ridges and creeklines. A. macdonnelliensis is drought and frost tolerant. Subspecies macdonnellensis is common in the MacDonnell Ranges to the Petermann Ranges in the Northern Territory, but is rare between them. It is only recorded from the Pollock Hills in Western Australia. Subspecies teretifolia is restricted to the Rawlinson Ranges in Western Australia extending to the Petermann Ranges in the Northern Territory.
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