Petrophile filifolia

Petrophile filifolia is a shrub that typically grows to a height of up to 0.5 m (1 ft 8 in). Its leaves are glabrous, curved, needle-shaped, 130–280 mm (5.1–11.0 in) long and 0.9–1.5 mm (0.035–0.059 in) wide. The flowers are arranged on the ends of branchlets in sessile, more or less spherical heads with a few narrow egg-shaped involucral bracts at the base. The flowers are about 17–25 mm (0.67–0.98 in) long, densely hairy and cream-coloured to pale yellow. Flowering mainly occurs from October to January and the fruit is a nut, fused with others in a oval head 15–28 mm (0.59–1.10 in) long and 14–20 mm (0.55–0.79 in) wide.[2][3]

Petrophile filifolia was first formally described in 1810 by Robert Brown in the Transactions of the Linnean Society of London.[4][5] The specific epithet (filifolia) means "thread-leaved".[6]

In 2005, Barbara Lynette Rye and Michael C. Hislop described two subspecies in the journal Nuytsia and the names are accepted by the Australian Plant Census:

• Petrophile filifolia R.Br. subsp. filifolia;[7]
• Petrophile filifolia subsp. laxa Rye & Hislop[8] that differs from the autonym in having flowers having longer hairs on the pollen presenter.[2]

This petrophile grows in a variety of habitats between Armadale, the Perup River, the Stirling Range and Albany in the Jarrah Forest biogeographical region of southwestern Western Australia.[3] Subspecies laxa grows in woodland and heath in the Armadale-Wandering area.[9]

Petrophile filifolia is classified as "not threatened"[3] but subsp. laxa is classified as "Priority Three" by the Government of Western Australia Department of Parks and Wildlife meaning that it is poorly known and known from only a few locations but is not under imminent threat.[9][10]