It is a shrub with grey-green leaves, mauve flowers and is endemic to Western Australia.

The leaves are linear to oblong shaped, upper surface grey-green, 20–95 mm (0.79–3.74 in) long, 1.5–2 mm (0.059–0.079 in) wide, margins rolled under, lower surface yellowish-green, wrinkled, thickly hairy, rounded apex on a petiole 2–3 mm (0.079–0.118 in) long.

The calyx lobes are mauve, pink-purple, sometimes white, each lobe with three distinct ribs, 1.5–2.5 cm (0.59–0.98 in) in diameter, divided to halfway, petals deep red, small, pedicel 8–15 mm (0.31–0.59 in) long and peduncles 18–50 mm (0.71–1.97 in) long.

Flowering occurs from May to September and the fruit is a woody, elliptic-shaped capsule.

[3][4] Guichenotia macrantha was first formally described in 1846 by Russian botanist Nikolai Turczaninow and the description was published in Bulletin de la Société Impériale des Naturalistes de Moscou.