Banksia petiolaris is a rare species of flowering plant in the family Proteaceae native to Western Australia, where it is found in sandy soils in the south coastal regions from Munglinup east to Israelite Bay.

B.  petiolaris is one of several closely related species that will all grow as prostrate shrubs, with horizontal stems and thick, leathery upright leaves.

It bears yellow cylindrical flower spikes, known as inflorescences, up to 16 cm (6+1⁄4 in) high in spring.

B. petiolaris adapts readily to cultivation, growing in well-drained sandy soils in sunny locations.

The first pair of leaves to appear after the cotyledons are 3.5 cm (1+3⁄8 in) long and oval in shape, with 2–3 lobes or teeth on each side.

[2] George Bentham published a thorough revision of Banksia in his landmark publication Flora Australiensis in 1870.

[3] In 1996, botanists Kevin Thiele and Pauline Ladiges published an arrangement informed by a cladistic analysis of morphological characteristics.

The placement of B. petiolaris in George's 1999 arrangement may be summarised as follows:[2] Since 1998, American botanist Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae, which includes Banksia.

[12] In a 2013 cladistics study, evolutionary scientists Marcell Cardillo and Renae Pratt found that its closest relative is B. brevidentata.

[13] Endemic to Western Australia, Banksia petiolaris is found near the state's south coast from the vicinity of Munglinup east to Israelite Bay,[2] concentrated in two disjunct ranges—an eastern one around Cape Arid National Park, and western one east of Scaddan.

It is found in white sandy soils in kwongan or mallee heathland, but sometimes occurs with the taller B. speciosa.

[14] Like many plants in Australia's Southwest, Banksia petiolaris is adapted to an environment in which bushfire events are relatively frequent.

[16] Many of its western populations are found on road verges, rendering them vulnerable to resurfacing or widening of roadways.

[14] It does, however, show little susceptibility to the soil-borne water mould Phytophthora cinnamomi, unlike many Western Australian banksias.

[1] B. petiolaris is grown fairly commonly in Australian gardens, making an attractive prostrate groundcover or rockery plant.