Banksia integrifolia


Banksia integrifolia, commonly known as the coast banksia, is a species of tree that grows along the east coast of Australia. One of the most widely distributed Banksia species, it occurs between Victoria and Central Queensland in a broad range of habitats, from coastal dunes to mountains. It is highly variable in form, but is most often encountered as a tree up to in height. Its leaves have dark green upper surfaces and white undersides, a contrast that can be striking on windy days.
It is one of the four original Banksia species collected by Sir Joseph Banks in 1770, and one of four species published in 1782 as part of Carolus Linnaeus the Younger's original description of the genus. It has had a complicated taxonomic history, with numerous species and varieties ascribed to it, only to be rejected or promoted to separate species. Modern taxonomy recognises three subspecies: B. integrifolia subsp. integrifolia, B. integrifolia subsp. compar and B. integrifolia subsp. monticola.
A hardy and versatile garden plant, B. integrifolia is widely planted in Australian gardens. It is a popular choice for parks and streetscapes, and has been used for bush revegetation and stabilisation of dunes. Its hardiness has prompted research into its suitability for use as a rootstock in the cut flower trade, but has also caused concerns about its potential to become a weed outside its natural habitat.

Names

Now widely known as the coast banksia or coastal banksia, B. integrifolia was previously known by a range of common names. The Checklist of Australian Trees lists four other common names: honeysuckle, white banksia, white bottlebrush and white honeysuckle; and some older sources refer to it as honeysuckle oak.
It was known to Indigenous Australians before its discovery and naming by Europeans; for example, the Gunai people of Gippsland called it birrna. Because of its wide range it would have a name in a number of other indigenous languages, but these are now lost. In 2001, a search of historical archives for recorded indigenous names of Victorian flora and fauna failed to find a single name for the species.

Description

B. integrifolia is a highly variable species. It is most often encountered as a tree up to in height, but in sheltered locations it can reach. In more exposed areas it may grow as a small, gnarled tree, reaching to no more than about, and in highly exposed positions, such as on exposed coastal headlands, it may even be reduced to a small shrub.
The tree usually has a single stout trunk, which is often twisted and gnarled, with the rough grey bark characteristic of Banksia. The leaves are dark green with a white underside, and occur in whorls of three to five. Adult leaves have entire margins. George specifies their dimensions as long and wide, but The Banksia Atlas warns that "Atlas contributors found great variability in these measurements with specimens often falling outside the varietal limits specified by George or being intermediate between two varieties." Juvenile leaves have dentate margins with a few short teeth, and are generally larger than adult leaves.
Flowers occur in Banksia's characteristic "flower spike", an inflorescence made up of several hundred flowers densely packed in a spiral around a woody axis. This is roughly cylindrical, high and wide. Flowers are usually pale yellow to yellow, but may be greenish or pinkish in bud. Each individual flower consists of a tubular perianth made up of four united tepals, and one long wiry style. Characteristic of the taxonomic section in which it is placed, the styles are straight rather than hooked. The style ends are initially trapped inside the upper perianth parts, but break free at anthesis. This process starts with the flowers at the bottom of the inflorescence, sweeping up the spike at an unusually high rate of between 96 and 390 flowers per 24 hours.
The flower spikes are not as prominent as in some other Banksia species, as they arise from two- to three-year-old nodes nested within the foliage. After flowering, old flower parts wither and fall away over a period of several months, revealing the "cone", a woody axis embedded with many small follicles. The follicles are initially greenish and downy, but gradually fade to dark grey. Each follicle contains one or sometimes two seeds, separated by a thin wooden separator. The seed itself is black, long with a feathery black 'wing' long.

Taxonomy

B. integrifolia was first collected at Botany Bay on 29 April 1770, by Sir Joseph Banks and Dr Daniel Solander, naturalists on the Endeavour during Lieutenant James Cook's first voyage to the Pacific Ocean. Solander coined the binomial name Leucadendrum integrifolium in Banks' Florilegium. However, the species was not published until April 1782, when Carolus Linnaeus the Younger described the first four Banksia species in his Supplementum Plantarum. Linnaeus distinguished the species by their leaf shapes, and named them accordingly. Thus the species with entire leaf margins was given the specific name integrifolia, from the Latin integer meaning 'entire' and folium 'leaf'. The full name for the species is therefore Banksia integrifolia L.f.
Then followed around 200 years of confusion over the taxonomic limits of the species, caused by the species' great variability, similarities with closely related species, and early attempts to classify the species based on dried specimen material alone. A stable Banksia taxonomy did not begin to emerge until 1981 with the publication of Alex George's landmark monograph The genus Banksia L.f. . Over the next 18 years, George's arrangement was gradually refined in the light of new research and the discovery of new material, and there were several changes to B. integrifolias infraspecific taxa. These changes culminated in George's 1999 arrangement, which had broad acceptance until 2005, when Austin Mast, Eric Jones and Shawn Havery published a phylogeny that did not accord with George's arrangement. A new taxonomic arrangement was not published at the time, but early in 2007 Mast and Thiele initiated a rearrangement by transferring Dryandra to Banksia, and publishing B. subg. Spathulatae for the species 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. integrifolia is placed in B. subg. Spathulatae; it is the type species for the subgenus.

Placement within ''Banksia''

The current taxonomic arrangement of the genus Banksia is based on George's 1999 monograph for the Flora of Australia book series. In this arrangement, B. integrifolia is placed in Banksia subg. Banksia, because its inflorescences take the form of Banksias characteristic flower spikes; Banksia sect. Banksia because of its straight styles; and Banksia ser. Salicinae because its inflorescences are cylindrical. Kevin Thiele additionally placed it in a subseries Integrifoliae, but this was not supported by George.
B. integrifolias placement within Banksia may be summarised as follows:
  • Genus Banksia
  • *Subgenus Isostylis
  • *Subgenus Banksia
  • **Section Oncostylis
  • **Section Coccinea
  • **Section Banksia
  • ***Series Grandes
  • ***Series Banksia
  • ***Series Crocinae
  • ***Series Prostratae
  • ***Series Cyrtostylis
  • ***Series Tetragonae
  • ***Series Bauerinae
  • ***Series Quercinae
  • ***Series Salicinae
  • ****B. dentata – B. aquilonia – B. integrifolia – B. plagiocarpa – B. oblongifolia – B. robur – B. conferta – B. paludosa – B. marginata – B. canei – ''B. saxicola''

    Subspecies

The names of three subspecies are accepted at the Australian Plant Census as at May 2020:
  • B. integrifolia subsp. compar K.R.Thiele;
  • B. integrifolia R.Br.subsp. integrifolia;
  • B. integrifolia subsp. monticola K.R.Thiele.
Although some of the great variability of B. integrifolia can be attributed to environmental factors, much is genetic: George writes that it "gives the impression that it is actively speciating to fill the many ecological niches through its range". Genetic variation across its range has been mapped in some detail with microsatellite markers, facilitating further analysis of intraspecific relationships. Fractal analysis of the shape and spectrum of the leaves has been used to determine to which subspecies plants of unknown provenance belong.
;Banksia integrifolia subsp. integrifolia
;Banksia integrifolia subsp. compar
;Banksia integrifolia subsp. ''monticola''

Hybrids

Presumed natural hybrids have been reported between B. integrifolia and other members of Banksia ser. Salicinae, although no hybrid names have been formally published to date. Presumed hybrids are identified by their intermediate features; for example those with B. paludosa, known from Jervis Bay and Green Cape on the coast of southern New South Wales, have a smaller habit, longer, thinner flower spikes, and persistent old flowers on old "cones", which are otherwise bare on pure B. integrifolia.
Presumed hybrids with B. marginata occur on Wilsons Promontory in Victoria; these are found in localities where both species co-occur, and have features intermediate between the two. Another purported hybrid with B. marginata, thought to be from Cape Paterson on Victoria's south coast, was first described by Alf Salkin and is commercially available in small quantities. It forms an attractive hardy low-growing plant to.