[1] Widespread throughout southwest Western Australia, it is found on sandy soils over laterite or limestone, often as an understorey plant in open forest, woodland or shrubland.
Encountered as a shrub or small tree up to 6 m (20 ft) in height, it has prickly dark green leaves and dome-shaped cream-yellow flowerheads.
Flowering from winter through to late spring, it provides a key source of food—both the nectar and the insects it attracts—for honeyeaters in the cooler months, and species diversity is reduced in areas where there is little or no parrot bush occurring.
As with most other Proteaceae, individual flowers consist of a tubular perianth made up of four united tepals, and one long wiry style.
The style end is initially trapped inside the upper perianth parts, but breaks free at anthesis.
Thus in B. sessilis, unlike many other Banksia species, the release of the style at anthesis does not result in a showy flower colour change.
[2][3] One field study found that anthesis took place over four days, with the outer flowers opening first and moving inwards.
[2][3] Specimens of B. sessilis were first collected by Scottish surgeon Archibald Menzies during the visit of the Vancouver Expedition to King George Sound in September and October 1791.
No firm location or collection date can be ascribed to Menzies' specimens, as their labels simply read "New Holland, King Georges Sound, Mr. Arch.
On his return to England in 1795, the surviving specimens were deposited into the herbarium of Sir Joseph Banks, where they lay undescribed for many years.
[9] The next collection was made in December 1801, when King George Sound was visited by HMS Investigator under the command of Matthew Flinders.
On board were botanist Robert Brown, botanical artist Ferdinand Bauer, and gardener Peter Good.
In the meantime, Joseph Knight published On the cultivation of the plants belonging to the natural order of Proteeae, which appeared to draw heavily on Brown's unpublished material, without permission, and in most cases without attribution.
[2] Blame for the alleged plagiarism largely fell on Richard Salisbury, who had been present at Brown's readings and is thought to have provided much of the material for Knight's book.
In that year, the colonial botanist of New South Wales Charles Fraser visited the area as part of an exploring expedition under James Stirling.
[28] The name holly-leaved dryandra was used when the plant was featured as part of a series of articles in the Western Mail of 1933–34,[29] and this was taken up by William Blackall in 1954,[30] and was still in use as late as 1970.
It also occurs in a range of vegetation complexes, including coastal and kwongan heath, tall shrubland, woodland and open forest.
It is a common understorey plant in drier areas of Jarrah forest,[2] and forms thickets on limestone soils of the Swan Coastal Plain.
[51] A field study in jarrah forest 9 km south of Jarrahdale, where B. sessilis grows in scattered clumps, found that western wattlebirds and New Holland honeyeaters sought out groups of plants with the greatest numbers of new inflorescences, particularly those one or two days after anthesis, where nectar yield was highest.
[4] Banksia sessilis is also a source of food for the Australian ringneck (Barnardius zonarius),[52] and the long-billed black cockatoo (Zanda baudinii), which tear open the follicles and consume the seeds.
[57] When self-fertilisation does occur, whether autogamous or geitonogamous, the resulting seed is almost always aborted,[54] and the species ultimately achieves an outcrossing rate of nearly 100%, at least in high density sites.
[57] The species is a prolific flowerer, and this, combined with the very high outcrossing rates, results in massive seed output.
[54][60] Regardless of the terminology used, the massive spontaneous seed output of B. sessilis is its primary survival strategy, and is so effective the species has a reputation as an excellent coloniser.
[64] Most highly susceptible species quickly become locally extinct in infected areas, and in the absence of hosts the disease itself eventually dies out.
It was recorded as being cultivated in the garden of Karl von Hügel in Vienna, Austria in 1831, and in 1833 it was listed amongst the rare plants that had been introduced into Belgium.
[70] One of the first published colour photographs of the species appeared in William Blackall's 1954 How to know Western Australian wildflowers, but this publication was restricted to plant identification.
[32][71] Possibly the first published information on the cultivation of Dryandra appeared in the magazine Australian Plants in June and September 1961.
[9] D. sessilis was among the species treated, but as there was not yet any experimental data on cultivation, information was restricted to its aesthetic qualities and the soil in which it naturally occurs.
[9] In 1965, John Stanley Beard published Descriptive catalogue of Western Australian plants, "a work of reference in which the horticultural characteristics of the plants concerned could be looked up by the staff", which described D. sessilis as an erect shrub with pale yellow flowers appearing from May to October, growing in sand and gravel.
[75] According to current knowledge, B. sessilis is an extremely hardy plant that grows in a range of soils and aspects, so long as it is given good drainage,[33] and tolerates both drought and moderate frost.