Swainsona longipilosa is a small annual plant in the family pea and is endemic to a small area in the central west of Western Australia. It has about 5 egg-shaped leaflets with the narrower end toward the base, and racemes of up to 3, reddish purple flowers.
Swainsona longipilosa is an annual plant that typically grows to a height of about . Its stems are about wide, densely softly-hairy and ribbed. The leaves are about long with about 5 egg-shaped leaflets with the narrower end towards the base, the side leaflets long and wide with stipules up to long at the base of the petioles. The flowers are arranged in racemes up to long with up to 3 flowers on a peduncle less than wide, each flower about long on a pedicel less than long. The sepals are joined at the base, forming a tube about long, the sepal lobes about the three times the length of the tube. The petals are reddish-purple, the standard petal about long and about wide, the wings long, and the keel long and deep.[1] Flowering has been observed in August and the fruit is oblong, about and wide.
Swainsona longipilosa was first formally described in 1993 by Joy Thompson in the journal Telopea from a specimen collected in 1981.[2] The specific epithet (longipilosa) means "long hair".
This species of swainsona is only known from two localities in Western Australia where it grows on a stony, exposed hilltop in Acacia woodland in the Carnarvon and Gascoyne bioregions.
Swainsona longipilosa is listed as "Priority One" by the Government of Western Australia Department of Biodiversity, Conservation and Attractions, meaning that it is known from only one or a few locations where it is potentially at risk.[3]