Banksia marginata, commonly known as the silver banksia, is a species of tree or shrub in the family Proteaceae found throughout much of southeastern Australia. It ranges from the Eyre Peninsula in South Australia to north of Armidale, New South Wales, and across Tasmania and the islands of Bass Strait. It grows in various habitats, including Eucalyptus forest, scrub, heathland and moorland. Banksia marginata varies widely in habit, ranging from a shrub to a tree. The narrow leaves are linear and the yellow inflorescences occur from late summer to early winter. These flower spikes fade to brown and then grey and develop woody follicles bearing the winged seeds. Originally described by Antonio José Cavanilles in 1800, further collections of B. marginata were designated as several separate species by Robert Brown in 1810. However, all were reclassified as a single species by George Bentham in 1870. No distinct subspecies have been recognised by Banksia expert Alex George, who nonetheless concedes that further work is needed.
Many species of bird, in particular honeyeaters, forage at the flower spikes, as do native and European honeybees. The response to bushfire varies. Some populations are serotinous: they are killed by fire and regenerate from large stores of seed, which have been held in cones in the plant canopy and are released after a fire. Others regenerate from underground lignotubers or suckers from lateral roots. Although it has been used for timber, Banksia marginata is most commonly seen as a garden plant, with dwarf forms being commercially propagated and sold.
Description
Banksia marginata is a highly variable species, usually ranging from a small shrub around a metre (3 ft) tall to a tree. Unusually large trees of 15 to possibly 30 m (50–100 ft) have been reported near Beeac in Victoria's Western District as well as several locations in Tasmania, while compact shrubs limited to high have been recorded on coastal heathland in Tasmania (such as at Rocky Cape National Park).Salkin, p. 145. Shrubs reach only high in Gibraltar Range National Park. The bark is pale grey and initially smooth before becoming finely tessellated with age. The new branchlets are hairy at first but lose their hairs as they mature, with new growth a pale or pinkish brown. The leaves are alternately arranged on the stems on 2–5 mm long petioles, and characteristically toothed in juvenile or younger leaves, which are long. The narrow adult leaves are dull green in colour and generally linear, oblong or wedge-shaped (cuneate) and measure long and wide. The margins become entire with age, and the tip is most commonly truncate or emarginate, but can be acute or mucronate. The cellular makeup of the leaves shows evidence of lignification, and the leaves themselves are somewhat stiff. Leaves also have sunken stomates. The leaf undersurface is white with a prominent midrib covered in brownish hairs.
The complex flower spikes, known as inflorescences, appear generally from late summer to early winter (February to June) in New South Wales and Victoria, although flowering occurs in late autumn and winter in the Gibraltar Range. Cylindrical in shape, they are composed of a central woody spike or axis, perpendicularly from which a large number of compact floral units arise. The flower spikes measure tall and wide. Pale yellow in colour, they are composed of up to 1,000 individual flowers (784 recorded in the Gibraltar Range) and arise from nodes on branchlets that are at least three years old. Sometimes two may grow from successive nodes in the same flowering season. They can have a grey or golden tinge in late bud. As with most banksias, anthesis is acropetal; the opening of the individual buds proceeds up the flower spike from the base to the top. Over time the flower spikes fade to brown and then grey, and the old flowers generally persist on the cone. The woody follicles grow in the six months after flowering, with up to 150 developing on a single flower spike. In many populations, only a few follicles develop. Small and elliptic, they measure long, high, and wide. In coastal and floodplain populations, these usually open spontaneously and release seed, while they generally remain sealed until burnt by fire in plants from heathland and montane habitats.Salkin, p. 146. Each follicle contains one or two fertile seeds, between which lies a woody dark brown separator of similar shape to the seeds. Measuring in length, the seed is egg- to wedge-shaped (obovate to cuneate) and composed of a dark brown wide membranous "wing" and wedge- or sickle-shaped (cuneate–falcate) seed proper, which measures long by wide. The seed surface can be smooth or covered in tiny ridges, and often glistens. The resulting seedling first grows two obovate cotyledon leaves, which may remain for several months as several more leaves appear. The cotyledons of Banksia marginata, B. paludosa and B. integrifolia are very similar in appearance.
Taxonomy and naming
Banksia marginata is commonly called the silver banksia, because the white undersides of its leaves contrast with the otherwise green foliage and give the plant a 'silvery' look. Alternate common names include honeysuckle and dwarf honeysuckle. The aboriginal name in the Jardwadjali language of western Victoria was , while the Kaurna name from the Adelaide Plains was pitpauwe and the local name in the Macquarie Harbour region in Tasmania was tangan.
A widely distributed and diverse plant, B. marginata was described independently and given many different names by early explorers. During his third voyage in January 1777, Captain James Cook reported a "most common tree [...] about ten feet high, branching pretty much, with narrow leaves, and a large, yellow, cylindrical flower, consisting only of a vast number of filaments; which, being shed, leave a fruit like a pine top." The genus Banksia was named in honor of Sir Joseph Banks, a botanist who was with Captain Cook during his first voyage (1768–1771) in which he circumnavigated the world, including stops in New Zealand and Australia (Botany Bay).Royal Botanic Gardens, Kew. Kew Science, Plants of the World Online. Accessed 2 December 2019. The species marginata was first collected by Luis Née in 1793, from somewhere between Sydney and Parramatta. In 1800, the Spanish botanist Antonio José Cavanilles gave the species the binomial name it still bears today. The species name is the Latin adjective marginatus ('bordered') and refers to appearance of the lower surface of the recurved margins of the leaves when viewed from underneath. Cavanilles also described another specimen collected by Née in the same locality as a different species, Banksia microstachya Cav. A smaller shrub with dentate leaves, this turned out to be an immature plant of the same species with juvenile leaves.Salkin, p. 25. Robert Brown described 31 species of Banksia in his 1810 work Prodromus Florae Novae Hollandiae et Insulae Van Diemen, including six taxa (B. marginata α and β plus four further species) now attributable to B. marginata. He split the genus into two subgenera, placing these species in subgenus Banksia verae, the "True Banksias". He described Banksia australis R.Br., giving the location of the collection as Port Phillip Bay in Victoria in 1802 (having crossed out Van Diemen's Land 1804). Brown's other collections which were reduced to synonymy with B. marginata were Banksia depressa R.Br., a prostrate shrub from Margate Rivulet in southeastern Tasmania, Banksia insularis R.Br., from Flinders and King Island, and Banksia patula R.Br., a shrub from the vicinity of Port Lincoln, South Australia. The French naturalist Aimé Bonpland in 1816 called it Banksia marcescens Bonpl., deemed an illegitimate name, as by that time the name Banksia marginata already had been published. Still more synonyms are Banksia ferrea Vent. ex Spreng. and Banksia gunnii Meisn.
By the time Carl Meissner published his 1856 arrangement of the genus, there were 58 described Banksia species. Meissner divided Brown's Banksia verae, which had been renamed Eubanksia by Stephan Endlicher in 1847, into four series based on leaf properties. He listed six species and a further four varieties all now sunk into B. marginata in series Salicinae.
In 1870, George Bentham published a thorough revision of Banksia in his landmark publication Flora Australiensis. In Bentham's arrangement, the number of recognised Banksia species was reduced from 60 to 46. Bentham observed that the characteristics Brown used to define B. australis, B. depressa, B. patula, and B. insularis were unable to distinguish separate forms as more specimens came to light, and hence declared them synonyms of B. marginata. Meissner's four series were replaced by four sections based on leaf, style and pollen-presenter characters. B. marginata was placed in section Eubanksia along with B. integrifolia and B. dentata.
Placement within Banksia The current taxonomic arrangement of the genus Banksia is based on botanist Alex George's 1999 monograph for the Flora of Australia book series. In this arrangement, B. marginata is placed in Banksia subgenus Banksia, because its inflorescences take the form of Banksia's characteristic flower spikes, section Banksia because of its straight styles, and series Salicinae because its inflorescences are cylindrical. In a morphological cladistic analysis published in 1994, Kevin Thiele placed it as the most basal member of a newly described subseries Integrifoliae, within the series Salicinae. However, this subgrouping of the Salicinae was not supported by George. George did concede that major work is needed on Banksia marginata, which shows such a high degree of variability over its range.
B. marginata'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
Since 1998, American botanist Austin Mast and co-authors have been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae, which then comprised genera Banksia and Dryandra. Their analyses suggest a phylogeny that differs greatly from George's taxonomic arrangement. Banksia marginata resolves as the closest relative, or "sister", to B. saxicola, the two taxa part of a larger group containing B. paludosa and the three subspecies of B. integrifolia. Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra into it, and published B. subg. Spathulatae for the taxa having spoon-shaped cotyledons; thus B. subg. Banksia was redefined as encompassing taxa lacking 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. marginata is placed in B. subg. Spathulatae.
Hybrids with other species Hybridisation with Banksia conferta subsp. penicillata at the site of an old abandoned railway between Newnes and Clarence in the Blue Mountains has been recorded; a single B. marginata plant was surrounded by plants with intermediate features but more strongly resembling B. conferta subsp. penicillata. B. marginata can also interbreed with B. paludosa where they are found together. A hybrid with B. saxicola was recorded from Mount William during the Banksia Atlas project.