Its unusual pinkish, pendent (hanging) flower spikes, known as inflorescences, are generally hidden in the foliage and appear during the early summer.

A bushy shrub, Banksia aculeata grows up to 2 m (7 ft) tall, with fissured grey bark on its trunk and branches.

[2] Appearing in February and March,[3] the cylindrical flower spikes—known as inflorescences—range from 6–9 cm (2+1⁄4–3+1⁄2 in) long, growing at the ends of short leafy 2–3-year-old side branches.

Hanging downward rather than growing upright like those of most other banksias, they are composed of a central woody spike or axis, from which many compact individual flowers arise perpendicularly.

It then splits at anthesis to reveal the smooth straight pistil, which is slightly shorter than its enveloping structure at 3.0–4.2 cm (1+1⁄4–1+3⁄4 in) long.

[4] The related Banksia caleyi is similar in appearance but can be distinguished by its recurved (downward curving) leaf margins, and smaller follicles and perianths.

[3] Banksia aculeata was first collected by James Drummond on one of his three trips to the Stirling Range between 1843 and 1848, though he did not regard it as distinct from B. caleyi—this was only recognised over a century later by Alex George.

For the type of the species, George selected a specimen he collected on Chester Pass Road in the Stirling Range east of Cranbrook on 20 March 1972.

Tetragonae was found to be monophyletic, and therefore retained; and their analysis of the relationships within the series supported the placement of B. aculeata alongside B. caleyi.

Under George's 1999 arrangement, B. aculeata's placement was as follows:[2] Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae.

His analyses suggest a phylogeny that is rather different from previous taxonomic arrangements, but support the placement of B. aculeata alongside B. caleyi in a clade corresponding closely with B. ser.

[6][7][8] A 2013 molecular study by Marcel Cardillo and colleagues using chloroplast DNA and combining it with earlier results found that B. aculeata was sister to B. lemanniana and that B. caleyi was the next closest relative.

[10] B. aculeata is native to the foothills of the Stirling Range in the southwest of Western Australia, occurring at elevations between 250 and 500 m (825 and 1,650 ft), in shrubland in gravelly, clayish soils.

[4] B. aculeata has been reported as susceptible to dieback from the soil-borne water mould Phytophthora cinnamomi,[14] but in a 2008 study this pathogen was found to have no direct impact on the species.

[16] Regarding its potential as an ornamental plant, Alex George observes that the flowers are brightly coloured but have a short life and are obscured by the foliage, which is quite prickly.