It is an erect shrub with prickly, pinnate or lobed leaves, and oblong or cylindrical heads of glabrous yellow to cream-coloured flowers.

The flowers are arranged on the ends of branchlets or in leaf axils in sessile, cylindrical heads 20–60 mm (0.79–2.36 in) long, with overlapping, egg-shaped involucral bracts at the base.

Flowering occurs from July to November and the fruit is a nut, fused with others in an oval to cylindrical head up to 65 mm (2.6 in) long.

[2][3] Petrophile macrostachya was first formally described in 1830 by Robert Brown in the Supplementum to his Prodromus Florae Novae Hollandiae et Insulae Van Diemen from material collected by Charles Fraser near the Swan River in 1827.

[6] Petrophile macrostachya grows in heath, shrubland and woodland from the Kalbarri National Park to near Gingin in the Avon Wheatbelt, Geraldton Sandplains, Jarrah Forest and Swan Coastal Plain biogeographic regions.