Banksia grossa

Banksia grossa grows as a bushy shrub, generally high, or occasionally up to high. New growth occurs in the spring and early summer. Flowers 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. One field study revealed, on average, eight follicles for each fertile cone. Initially covered in fine fur, these are long, high and jut out by . The fur rubs off and they become smooth with wear, and generally remain closed until opened by fire. Seeds The seeds of Banksia grossa are the largest of all the species of the series Abietinae. Measuring long, they are made up of a cuneate (wedge-shaped) seed body, long by wide, and a wide wing. The woody separator is the same shape as the seed, with an impression where the seed body lies next to it. The bright green cotyledons are obovate and can be either convex or concave, measuring 1.6 to 2.2 cm long by 0.9 to 1.2 cm wide. These arise from a stocky seedling stem, known as the hypocotyl, which is reddish and covered in short hairs. The auricles of the cotyledons are 2 mm long. Seedling leaves arise 0.6 to 0.8 cm beyond the cotyledons and are oppositely arranged. Linear, they are 1.4 to 1.6 cm long with recurved margins and are covered in white hair. The stem remains reddish. Subsequent leaf pairs are successively longer. ==Taxonomy==

The first known specimen collection of B. grossa was made by botanist Fred W. Humphreys in 1965. 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. It was placed in phyletic order between B. micrantha and B. leptophylla. The specific epithet is from the Latin grossus ("coarse") and refers to the leaves, flowers, and fruit, all of which George observed were more coarse than other members of B. ser. Abietinae. 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. ==Distribution and habitat==

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. Around 40% of plants occur on road verges. ==Ecology==

Banksia grossa resprouts from its woody lignotuber after bushfire. Shrubs carry relatively low numbers of seeds compared with plant species that regenerate by seed after bushfire. A field study in Eneabba showed shrubs bore anywhere from 30 to 90 seeds per plant. Seeds borne on plants, however, are less likely to be eaten by animals than seed lying dormant in the soil, and hence survive to produce future seedlings. Populations of resprouting plants, like B. grossa, benefit more from longer intervals between fires as their stored seedbank takes longer to accumulate than reseeding species. 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 and 90% after . 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. ==Use in horticulture==

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. ==Cultural references==

This banksia was featured on an Australian postage stamp in 2018. ==Notes==