Acacia declinata is a shrub of the genus Acacia and the subgenus Plurinerves that is endemic to an area along the south coast in south western Australia.
The dense pungent shrub typically grows to a height of 0.2to and has a prostrate habit. It has terete and densely haired branchlets with semi-persistent triangular stipules that are around in length. Like most species of Acacia it has phyllodes rather than true leaves. The sessile, patent to reflexed, glabrous and evergreen phyllodes are straight to shallowly recurved with a length of and a diameter of and have a brown tip with three nerves per face.[1] It blooms from August to September and produces yellow flowers.
The species was first formally described by the botanists Richard Sumner Cowan and Bruce Maslin in 1990 in the work A new species of Acacia from Western Australia as published in the journal the Western Australian Naturalist. It was reclassified as Racosperma declinatum by Leslie Pedley in 2003 then returned to genus Acacia in 2014.[2]
It is native to an area in the Great Southern region of Western Australia where it is found growing in loamy or sandy clay soils. It is found in an area between Borden in the north west, Manypeaks in the south west and Boxwood Hill in the south east where it is often a part of tall shrubland a woodland communities.[1]