Banksia grossa is a species of shrub in the family Proteaceae and is endemic to Southwest Australia.

It is one of fourteen species of banksia of the series Abietinae, all of which bear predominantly cylindrical or oval inflorescences.

Its thick leaves and large seeds distinguish it from other members of the Abietinae, and are the basis of its species name.

Found in sand or sand over laterite among heath between Eneabba and Badgingarra in Western Australia, the species grows as a many-stemmed shrub to 1 m (3.3 ft) high with narrow leaves and oval brownish flower spikes up to 10 cm (4 in) high, composed of hundreds of individual flowers.

The margins of the leaves are straight with no teeth and rolled over, and the upper surfaces are sparsely hairy when young, but later hairless.

The opening of flowers occurs sequentially, starting at the bottom of the inflorescence and sweeping through to the top over a period of around two weeks.

Alex George has expressed surprise that it was not collected by earlier visitors to the area, speculating that "perhaps they were diverted by its similarity to B. leptophylla and B. sphaerocarpa."

George formally described the species in his 1981 monograph "The genus Banksia L.f. (Proteaceae)", based on a specimen collected by him on the Brand Highway, 76 km north of Regans Ford, on 14 May 1969.

He placed it in subgenus Banksia because of its flower spike; section Oncostylis because its styles are hooked; and the resurrected series Abietinae, which he constrained to contain only round-fruited species.

caesia This clade became the basis for the new subseries Sphaerocarpae, which Thiele defined as containing those species with lignotubers, styles loosely curling around the infructescence (although this trait was reversed in B. micrantha), and "transversely aligned cells of the seed wing inner face".

The placement of B. grossa in George's 1999 arrangement may be summarised as follows:[4] Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae.

leptophylla B. lanata B. grossa Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subg.

[11] Banksia grossa mainly occurs from west of Yandanooka in the north, south to Badgingarra National Park, and east almost to Coorow.

The trichomes (leaf hairs) run along the mid-vein and the margins, further protecting the surface where the stomates are located, thus minimising water loss.

[14] Large numbers of ladybirds have been reported drinking the nectar of this species, while ignoring nearby Banksia attenuata inflorescences.

[a] Whereas other Banksia species produce nectar that is clear and watery, the nectar of these species is pale yellow initially, but gradually becomes darker and thicker, changing to a thick, olive-green mucilage within one to two days of secretion, and eventually becoming "an almost black, gelatinous lump adhering to the base of the flowers".

Noting that many of these cyanobacteria had heterocysts, he speculated that they aid the plant by fixing atmospheric nitrogen, which is then washed off the flower heads by rain, and absorbed by the proteoid root mat.

[18] Further investigation by Markey and Lamont in 1996 suggested that the discolouration is not caused by cyanobacteria or other microorganisms in the nectar, but is rather "a chemical phenomenon of plant origin".

[19] The purpose of coloured nectar is unclear, especially as pollinators such as nocturnal mammals are not thought to forage by sight.

[16] Banksia grossa is cultivated for its attractive needle-like leaves and rusty-brown flower spikes, both of which can be quite variable in colour.

This species favours well-drained sandy or loamy acidic soils with a pH of 5.5 to 7, and a sunny aspect.