Banksia alliacea is a species of shrub that is endemic to southwestern Western Australia.

[2] The composite flower heads, known as inflorescences, grow from the ends of stems and give off an onion-like smell.

As the name "Banksia nervosa" had already been published by Otto Kuntze for the plant now known as Pimelea angustifolia, Mast and Thiele were forced to choose a new specific epithet; their choice, "alliacea", is from the Latin alliaceus ("onion-like"), in reference to scent of the flowers.

[5] Genetic analysis by Marcell Cardillo and Renae Pratt indicate that its sister species is Banksia pellaeifolia.

It grows in flat areas on clay-loam or sandy loam with a yearly rainfall of 400 to 800 millimetres (16 to 31 in).