Banksia idiogenes is a tufted shrub up to about 70 cm (28 in) in diameter with hairy stems, but does not form a lignotuber. The leaves are deeply pinnatifid, 150–370 mm (5.9–14.6 in) long and 12–38 mm (0.47–1.50 in) wide on a petiole up to 90 mm (3.5 in) long. There are between twenty and twenty-five triangular lobes up to 19 mm (0.75 in) long on each side of the leaves and the lower surface has a prominent network of veins. The flowers are strongly scented and arranged in groups of about eighty in a head on the ends of branches, often the heads close together. There are linear to lance-shaped, papery involucral bracts up to 45 mm (1.8 in) long at the base of the head. The flowers have a perianth 36–44 mm (1.4–1.7 in) long that is white near the base and deep red near the end, and a cream-coloured pistil 35–39 mm (1.4–1.5 in) long. Flowering occurs in August and several egg-shaped, glabrous follicles 12–13 mm (0.47–0.51 in) long form in each head.^[2][3][4]

This species was first formally described by Alex George in 1996 in the journal Nuytsia and given the name Dryandra idiogenes, from material he collected near Newdegate in 1986.^[5] The specific epithet (idiogenes) is an ancient Greek word meaning "distinctive" or "peculiar", in reference to this species' unusual bracts and strongly scented red and white flowers.^[4]

In 2007, Austin Mast and Kevin Thiele transferred all the dryandras to the genus Banksia and this species became Banksia idiogenes.^[6][7]

Banksia idiogenes grows in kwongan and is only known from several small populations in a small area near Newdegate in the Mallee biogeographic region.^[2][3][4]

This banksia is classified as "Priority Two" by the Western Australian Government Department of Parks and Wildlife^[2] meaning that it is poorly known and from only one or a few locations.^[8]