Swainsona pterostylis is a species of flowering plant in the family Fabaceae and is endemic to northern parts of Western Australia. It is a low-growing or prostrate perennial herb, with imparipinnate leaves with mostly 11 to 19 broadly elliptic leaflets, and racemes of 5 to more than 30 purple or violet flowers.
Swainsona pterostylis is low-growing or prostrate perennial herb, that typically grows to a height of up to about high, and usually has 3 hairy stems. Its leaves are imparipinnate, mostly long on a petiole, with mostly 11 to 19, broadly elliptic to narrowly egg-shaped with the narrower end towards the base, the side leaflets long and wide. There is a stipule long at the base of the petiole. The flowers are arranged in racemes long with 5 to more than 30 flowers on a peduncle about wide, each flower long on a pedicel long. The sepals are joined at the base, forming a tube about long, the sepal lobes equal to or about as long as the tube. The petals are purple to violet, the standard petal about long and wide, the wings long, and the keel about long and deep.[1] Flowering occurs from April to October, and the fruit is oblong to almost spherical, long and wide.
This species was first formally described in 1825 by Augustin Pyramus de Candolle who gave it the name Astragalus pterostylis in his Prodromus Systematis Naturalis Regni Vegetabilis.[2] In 1967, Reinier van den Brink transferred the species to Swainsona as S. pterostylis. The specific epithet (pterostylis) means "having a style".[3]
Swainsona pterostylis grows on coastal sandhills and red claypans, often in limy or salty soils in the Avon Wheatbelt, Carnarvon, Dampierland, Gascoyne, Geraldton Sandplains, Great Sandy Desert, Murchison, Pilbara and Yalgoo bioregions of northern Western Australia.