Acacia undosa

The dense spreading shrub typically grows to a height of 0.3 to 1.5 metres (1 to 5 ft)^[1] and has a domed or obconic habit with hairy branchlets with persistent slender stipules that taper to a point and have a length of about 2 mm (0.079 in). Like most species of Acacia it has phyllodes rather than true leaves. The rigid, glabrous and pungent phyllodes have a linear to linear-oblanceolate shape and are straight to slightly curved with a length of 2 to 4.5 cm (0.79 to 1.77 in) and a width of 1 to 4 mm (0.039 to 0.157 in) and terminate with a rigid point.^[2] It blooms from July to September and produces yellow flowers.^[1] The simple inflorescences occur in pairs in the axils and have spherical flower-heads with a diameter of 3 to 3.5 mm (0.12 to 0.14 in) containing 18 to 20 golden coloured flowers. The pimply looking and crustaceous seed pods form that have a linear shape but are strongly undulate with a length of 1 to 4 cm (0.39 to 1.57 in) and a width of 2.5 mm (0.098 in) with a distinct pale marginal nerve. The dark brown seeds inside the pods have an elliptic-oblong to broadly oblong-elliptic shape with a length of 2.2 to 2.7 mm (0.087 to 0.106 in).^[2]

The species was first formally described by the botanists Richard Sumner Cowan and Bruce Maslin in 1995 as a part of the work Acacia Miscellany. Five groups of microneurous species of Acacia (Leguminosae: Mimosoideae: section Plurinerves), mostly from Western Australia as published in the journal Nuytsia. It was reclassified as Racosperma undosum by Leslie Pedley in 2003 then transferred back to genus Acacia in 2006.^[3]