Banksia grossa

Shrub in the family Proteaceae endemic to Australia

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. Collected in 1965, it was first formally described in 1981 by Alex George. 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 high with narrow leaves and oval brownish flower spikes up to high, composed of hundreds of individual flowers. Flowering occurs throughout the cooler months of March to September. Flower spikes develop woody follicles which bear the seeds. After bushfire, Banksia grossa regenerates from its woody lignotuber; bushfires also stimulate the release of seeds, which germinate after disturbance. Visitors to (and likely pollinators of) inflorescences include insects and a nocturnal mammal, the white tailed dunnart.

Banksia grossa grows as a bushy shrub, generally high, or occasionally up to high. New growth occurs in the spring and early summer.

Flowers occur in a typical Banksia flower spike: an inflorescence made up of hundreds of small individual flowers, or florets, densely packed around (and completely obscuring) a woody cylindrical axis. In B. grossa, this axis is high with a diameter of From this, the florets radiate out laterally, giving the inflorescence a diameter of After flowering, the old florets wither and curl against the spike, giving it a hairy appearance. Now known as an infructescence, it is roughly ellipsoidal, 6 to 10 cm high (2.2–4 in) and wide. Up to 25 smooth, elliptical follicles develop on the spike, each containing up to two wide wedge shaped winged seeds. Questioning the emphasis on cladistics in Thiele and Ladiges' arrangement, George published a slightly modified version of his 1981 arrangement in his 1999 treatment of Banksia for the Flora of Australia series of monographs. The placement of B. grossa was the same as in 1981, except that B. telmatiaea was moved to set between it and B. leptophylla. The placement of B. grossa in George's 1999 arrangement may be summarised as follows:

Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subg. Spathulatae for the taxa having spoon shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. grossa is placed in B. subg Spathulatae.

Banksia grossa mainly occurs from west of Yandanooka in the north, south to Badgingarra National Park, and east almost to Coorow. It grows in shallow sand over laterite, in deep sand, and occasionally atop lateritic rises, on flat or gently undulating land, among kwongan shrubland. The follicles generally open after bushfire, releasing seeds which germinate after disturbance. Species with persistent flowers on old spikes often require higher temperatures for follicles to open after burning; laboratory testing resulted in 50% opening after exposure to 270 °C and 90% after 400 °C. Cladistic analysis suggests this species and its relatives in the series Abietinae developed long narrow leaves with inrolled margins as they invaded drier climates in Australia's southwest, having evolved from ancestors with broad leaves. Large numbers of ladybirds have been reported drinking the nectar of this species, while ignoring nearby Banksia attenuata inflorescences. No pollinators of this species were recorded in The Banksia Atlas survey. It was first noted by Byron Lamont in 1980; he attributed it to cyanobacteria that feed off the nectar sugars. 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. This purported symbiosis was investigated by Barrett and Lamont in 1985, but no evidence of nitrogen fixing was found. 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". Their analyses indicated that the nectar had unusually high levels of sugar and free amino acids, The purpose of coloured nectar is unclear, especially as pollinators such as nocturnal mammals are not thought to forage by sight. However, nectar that becomes more obvious by appearance or smell as it ages might encourage pollinators to prioritise it over newer nectar. It is possible the colour change is unrelated to pollination.

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. Once established, it tolerates dry spells. It can be pruned heavily as it resprouts from its lignotuber. Propagation is by seed. This is a slow growing plant, taking 5 to 7 years to reach maturity and begin flowering.