Members of subgenus Isostylis have dome-shaped flower heads that are superficially similar to those of B. ser.

Dryandra, but structurally more like reduced versions of the "flower spikes" characteristic of most other Banksia taxa.

Isostylis was first published by Robert Brown in his 1810 Prodromus Florae Novae Hollandiae et Insulae Van Diemen; thus its full name, with author citation, is Banksia subg.

[1] Twenty years later, Brown issued a supplement to his Prodromus entitled Supplementum Primum Prodromi Florae Novae Hollandiae; another nine Banksia species were published, but there was no change to the 1810 arrangement, and no new Isostylis species.

[6] When Carl Meissner published his arrangement of Banksia in 1856, he demoted both of Brown's subgenera to sectional rank, maintaining B. sect.

integrifolia, based on specimens collected by Ludwig Preiss near the Swan River in Western Australia.

The next change to Isostylis came in 1981, when Alex George promoted it back to subgenus rank, and published a second species, B. cuneata.

In discussing the subgenus, George commented that there had been calls to transfer Isostylis into Dryandra, which was then a distinct genus.

In 1996, Kevin Thiele and Pauline Ladiges published a revised arrangement based on a cladistic analysis of morphological characters of Banksia.

Isostylis was unaffected and can be summarised 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 has provided compelling evidence for the paraphyly of Banksia with respect to Dryandra, and suggest an overall phylogeny that is very greatly different from George's arrangement.

[8][9][10] Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subg.

They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, B. subg.

Further complicating the situation is the existence of a population of B. cuneata having both genetic and phenetic affinities with B. oligantha.

B. ilicifolia is widespread within 70 kilometres of the coast from Mount Lesueur in the north, south to Cape Leeuwin and east to Albany.

They lack a lignotuber, so shrubs are killed by bushfire; mature trees of B. ilicifolia have a limited ability to resprout from epicormic buds on the trunk.

Threats include loss of habitat, Phytophthora cinnamomi dieback, and grazing on seedlings by feral rabbits.