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 . 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 (1981) 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 ''Banksias characteristic "flower spike", an inflorescence made up of several hundred flowers densely packed in a spiral 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 (later Captain) James Cook's first voyage to the Pacific Ocean. 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 , meaning "entire", and , meaning "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. (Proteaceae)''. 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. integrifolia''s 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 ''Banksia''s 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. integrifolia''s 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'' ( R.Br.) 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 relationshops. Fractal analysis of the shape and spectrum (colour) of the leaves has been used to determine to which subspecies plants of unknown provenance belong.

;''Banksia integrifolia'' subsp. ''integrifolia''
:The nominate subspecies occurs near the coast over most of the species' range except the far north. It varies little except in northern New South Wales and southern Queensland, where some populations appear to be intermediate with ''B. integrifolia'' subsp. ''compar''.
;''Banksia integrifolia'' subsp. ''compar''
:This subspecies grows in coastal Queensland as far north as Proserpine. For most of its range it is the only subspecies, but near its southern limit it co-occurs with ''B. integrifolia'' subsp. ''integrifolia''. The two subspecies are distinguishable by their leaves, which are larger and glossy with wavy margins on ''B. integrifolia'' subsp. ''compar''.
;''Banksia integrifolia'' subsp. ''monticola''
:Commonly known as white mountain banksia, it is the only subspecies with a montane distribution; it occurs in the Blue Mountains of northern New South Wales. It is similar in form to ''B. integrifolia'' subsp. ''integrifolia'', but differs in having longer, narrower leaves, and follicles that are more deeply embedded in the old flower spike.

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'' (swamp banksia), 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''.
Salkin, Abraham Isaac (Alf) (1979). "Variation in ''Banksia'' in Eastern Australia". (MSc thesis). Clayton, Victoria: Monash University.

Presumed hybrids with '' B. marginata'' (silver banksia) 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 .

Distribution and habitat

''B. integrifolia'' is widely distributed, in both geographical and ecological terms. According to Alex George, "it spans a wider geographical and climatic range than any other species." Thiele and Ladiges make a similar claim: that its distribution "is a broader latitudinal, altitudinal and ecological amplitude than any other species, with the possible exception of '' B. spinulosa''." No other species of tree occurs closer to the coast at Cape Byron, making ''B. integrifolia'' the most easterly tree on the Australian mainland.

It occurs along almost the entire eastern coast of Australia, from Geelong, Victoria to Proserpine, Queensland. There was an isolated population on Long Island, Tasmania in 1999, and an 1876 record allegedly from King Island, although there has been speculation that that specimen was actually collected in the Furneaux Group. The species no longer occurs at any of these Tasmania locations, and has been declared extinct in Tasmania under that state's ''Threatened Species Protection Act 1995''. The range of latitude is thus about 20° to 38°S.

For most of its distribution, ''B. integrifolia'' occurs only within about of the coast, where it typically occurs on poor quality sandy soils derived from sandstone. It grows near coastal cliffs and headlands, alongside river estuaries, and even on stabilised sand dunes. The temperature range for this area is around , with almost no frosts. The species can occur in pure stands, but is usually associated with other species such as ''Melaleuca quinquenervia'' (broad-leaved paperbark), ''Angophora costata'' (smooth-barked apple), ''Corymbia gummifera'' (red bloodwood), ''Eucalyptus botryoides'' (bangalay), ''Monotoca elliptica'' (wedding bush) and ''Leptospermum laevigatum'' (coast tea tree).

Between Sydney and Brisbane, ''B. integrifolia'' is found up to inland, with ''B. integrifolia'' subsp. ''monticola'' occurring in the Blue Mountains at altitudes up to . There it grows on better quality volcanic or rocky soils derived from granites and basalts, and would experience up to 100 frosts per year. In this montane habitat, it occurs in association with ''Eucalyptus'' species such as ''E. viminalis'' (manna gum) and ''E. pauciflora'' (snow gum), and also rainforest species such as ''Nothofagus moorei'' (Antarctic beech) and ''Orites excelsa'' (prickly ash).

Ecology

Like most other Proteaceae, ''B. integrifolia'' has proteoid roots, roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter. These enhance solubilisation of nutrients, thus allowing nutrient uptake in low-nutrient soils such as the phosphorus-deficient native soils of Australia. Studies on ''B. integrifolia'' suggest that its proteoid root mat achieves this by chemically modifying its soil environment.

''B. integrifolia'' flowers have an unusually short life span for ''Banksia'' species, producing nectar for only about four to twelve days after anthesis. Most nectar is produced during the night and early in the morning, with only small amounts produced during the day. Flowers are produced all through the year, but there is a strong peak in autumn. Little else flowers within its range at this time, so it is a seasonally important source of food for nectariferous animals. Surveys have observed a range of animals feeding on the species, including a wide range of insects; many species of bird including '' Phylidonyris novaehollandiae'' (New Holland honeyeater), ''Anthochaera carunculata'' (red wattlebird), '' Anthochaera chrysoptera'' (little wattlebird), '' Acanthorhynchus tenuirostris'' (eastern spinebill) and ''Trichoglossus haematodus'' (rainbow lorikeet); and mammals such as ''Petaurus norfolcensis'' (squirrel glider), '' Petaurus breviceps'' (sugar glider), '' Acrobates pygmaeus'' (feathertail glider), ''Pteropus poliocephalus'' (grey-headed flying fox), and ''Syconycteris australis'' common blossom bat. In some areas such as at Bungawalbin National Park in northern New South Wales, ''B. integrifolia'' is the only source of nectar and pollen in the autumn (March–April) and late winter (July). The importance of non-flying mammals to pollination of ''B. integrifolia'' was demonstrated in 1989, with a study in Wilsons Promontory National Park showing a reduction of fruit set when measures were taken to exclude them. ''Banksia integrifolia'' is the host plant of the lichen

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