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| Banksia | |
|---|---|
 | |
| Banksia serrata | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Proteales |
| Family: | Proteaceae |
| Subfamily: | Grevilleoideae |
| Tribe: | Banksieae |
| Genus: | Banksia L.f. |
| Type species | |
| Banksia serrata | |
| Diversity | |
| About 170 species | |
 | |
| Distribution ofBanksia withinAustralia | |
| Synonyms[1] | |
Banksia is agenus of around 170species offlowering plants in the familyProteaceae.[1] These Australianwildflowers and populargarden plants are easily recognised by their characteristic flower spikes, and woody fruiting "cones" and heads.[2]: 1 Banksias range in size from prostrate woodyshrubs to trees up to 30 metres (100 ft) tall. They are found in a wide variety of landscapes:sclerophyll forest, (occasionally) rainforest, shrubland, and some more arid landscapes, though not in Australia's deserts.
Heavy producers ofnectar, banksias are a vital part of the food chain in the Australian bush. They are an important food source for nectarivorous animals, including birds, bats, rats, possums, stingless bees and a host of invertebrates. Further, they are of economic importance to Australia'snursery andcut flower industries. However, these plants are threatened by a number of processes includingland clearing, frequent burning and disease, and a number of species arerare andendangered.
Banksias grow astrees or woodyshrubs. Trees of the largest species,B. integrifolia (coast banksia) andB. seminuda (river banksia), often grow over 15 metres tall, some even grow to standing 30 metres tall.[3]Banksia species that grow as shrubs are usually erect, but there are several species that are prostrate, with branches that grow on or below the soil.
The leaves ofBanksia vary greatly between species. Sizes vary from the narrow, 1–1+1⁄2 centimetre long needle-like leaves ofB. ericifolia (heath-leaved banksia), to the very large leaves ofB. grandis (bull banksia), which may be up to 45 centimetres long. The leaves of most species have serrated edges, but a few, such asB. integrifolia, do not. Leaves are usually arranged along the branches in irregular spirals, but in some species they are crowded together inwhorls. Many species have differing juvenile and adult leaves (e.g.,Banksia integrifolia has large serrated juvenile leaves).
The flowers are arranged in flower spikes or capitate flower heads.[4] The character most commonly associated withBanksia is the flower spike, an elongatedinflorescence consisting of a woody axis covered in tightly packed pairs of flowers attached at right angles. A single flower spike generally contains hundreds or even thousands of flowers; the most recorded is around 6000 on inflorescences ofB. grandis. Not allBanksia have an elongate flower spike, however: the members of the smallIsostylis complex have long been recognised asbanksias in which the flower spike has been reduced to a head; and recently the large genusDryandra has been found to have arisen from within the ranks ofBanksia, and sunk into it asB. ser.Dryandra. They similarly have capitate flower heads rather than spikes.
Banksia flowers are usually a shade ofyellow, butorange,red,pink and evenviolet flowers also occur. The colour of the flowers is determined by the colour of theperianth parts and often thestyle. The style is much longer than the perianth, and is initially trapped by the upper perianth parts. These are gradually released over a period of days, either from top to bottom or from bottom to top. When the styles and perianth parts are different colours, the visual effect is of a colour change sweeping along the spike. This can be most spectacular inB. prionotes (acorn banksia) and related species, as the white inflorescence in bud becomes a brilliant orange. In most cases, the individual flowers are tall, thin saccate (sack-shaped) in shape.
Occasionally, multiple flower spikes can form. This is most often seen inBanksia marginata andB. ericifolia[5][6](pictured right).
As the flower spikes or heads age, the flower parts dry up and may turn shades of orange, tan or dark brown colour, before fading to grey over a period of years. In some species, old flower parts are lost, revealing the axis; in others, the old flower parts may persist for many years, giving the fruiting structure a hairy appearance. Old flower spikes are commonly referred to as "cones", although they are not technically cones according to the botanical definition of the term:cones only occur inconifers andcycads.
Despite the large number of flowers per inflorescence, only a few of them ever develop fruit, and in some species a flower spike will set no fruit at all. The fruit ofBanksia is a woodyfollicle embedded in the axis of the inflorescence. In many species, the resulting structure is a massive woody structure commonly called a cone. Each follicle consists of two horizontal valves that tightly enclose the seeds. The follicle opens to release the seed by splitting along the suture. In some species, each valve splits too. In some species the follicles open as soon as the seed is mature, but in most species most follicles open only after stimulated to do so bybushfire. Each follicle usually contains one or two small seeds, each with a wedge-shaped papery wing that causes it to spin as it falls to the ground.
Specimens ofBanksia were first collected bySir Joseph Banks andDaniel Solander, naturalists on theEndeavour during Lieutenant (later Captain)James Cook's first voyage to thePacific Ocean. Cook landed on Australian soil for the first time on 29 April 1770, at a place that he later namedBotany Bay in recognition of "the great quantity of plants Mr Banks and Dr Solander found in this place".[7] Over the next seven weeks, Banks and Solander collected thousands of plant specimens, including the first specimens of a new genus that would later be namedBanksia in Banks' honour. Four species were present in this first collection:B. serrata (Saw Banksia),B. integrifolia (Coast Banksia),B. ericifolia (Heath-leaved Banksia) andB. robur (Swamp Banksia). In June the ship wascareened atEndeavour River, where specimens ofB. dentata (Tropical Banksia) were collected.[8]
The genusBanksia was finally described and named byCarolus Linnaeus the Younger in his April 1782 publicationSupplementum Plantarum; hence thefull name for the genus is "Banksia L.f.". Linnaeus placed the genus in classTetrandra, order Monogynia of his father's classification,[9] and named it in honour of Banks. The nameBanksia had in fact already been published in 1775 asBanksiaJ.R.Forst &G.Forst, referring to someNew Zealand species that the Forsters had collected during Cook's second voyage. However Linnaeus incorrectly attributed the Forsters' specimens to the genusPasserina, and therefore considered the nameBanksia available for use. By the timeJoseph Gaertner corrected Banks' error in 1788,Banksia L.f. was widely known and accepted, so GaertnerrenamedBanksia J.R.Forst, & G.Forst toPimelea, a name previously chosen for the genus by Banks and Solander.[10]
The first specimens of aDryandra were collected byArchibald Menzies, surgeon and naturalist to theVancouver Expedition. At the request ofJoseph Banks, Menzies collected natural history specimens wherever possible during the voyage. During September and October 1791, while the expedition were anchored atKing George Sound, he collected numerous plant specimens, including the first specimens ofDryandra (now Banksia) sessilis (Parrotbush) andD. (now Banksia) pellaeifolia. Upon Menzies' return to England, he turned his specimens over to Banks; as with most other specimens in Banks' library, they remained undescribed for many years.[11] Robert Brown gave a lecture, naming the new genusDryandra in 1809, howeverJoseph Knight published the nameJosephia before Brown published his paper with the description ofDryandra. Brown ignored Knight's name, as did subsequent botanists.[12]
In 1891,Otto Kuntze, strictly applying theprinciple of priority, argued thatPimelea should revert to the nameBanksia J.R.Forst & G.Forst. He proposed the new genusSirmuellera to replacedBanksia L.f. and transferred its species to the new genus.[13] This arrangement was largely ignored by Kuntze's contemporaries.[14]Banksia L.f. wasformally conserved andSirmuellera rejected in 1940.[15]
Banksia belongs to the familyProteaceae, subfamilyGrevilleoideae, and tribeBanksieae. There are around 170 species. The closest relatives ofBanksia are two genera of rainforest trees in North Queensland (Musgravea andAustromuellera).[16]
Alex George arranged the genus into two subgenera—subgenusIsostylis (containingB. ilicifolia,B. oligantha andB. cuneata) and subgenusBanksia (containing all other species except those he considered dryandras)—in his 1981 monograph and 1999 treatment for the Flora of Australia series. He held that flower morphology was the key to relationships in the genus. Austin Mast and Kevin Thiele published the official merging ofDryandra withinBanksia in 2007, recalibrating the genus into subgenusBanksia and subgenusSpathulatae.[17]
All but one of the livingBanksia species areendemic to Australia. The exception isB. dentata (tropical banksia), which occurs throughout northern Australia, and on islands to the north includingNew Guinea and theAru Islands.[18]: 148–149, 205 An extinct species,B. novae-zelandiae, was found inNew Zealand. The other species occur in two distinct geographical regions:southwestWestern Australia and eastern Australia. Southwest Western Australia is the main centre ofbiodiversity; over 90% of allBanksia species occur only there, fromExmouth in the north, south and east to beyondEsperance on the south coast. Eastern Australia has far fewer species, but these include some of best known and most widely distributed species, includingB. integrifolia (coast banksia) andB. spinulosa (hairpin banksia). Here they occur from theEyre Peninsula in South Australia right around the east coast up toCape York inQueensland.
The vast majority ofBanksia are found in sandy or gravelly soils, though some populations ofB. marginata (silver banksia) andB. spinulosa do occur on soil that is heavier and more clay-like.B. seminuda is exceptional for its preference for rich loams along watercourses.
Most occur inheathlands or lowwoodlands; of the eastern species,B. integrifolia andB. marginata occur in forests; many south-western species such asB. grandis,B. sphaerocarpa,B. sessilis,B. nobilis andB. dallanneyi grow as understorey plants injarrah (Eucalyptus marginata), wandoo (E. wandoo) andkarri (E. diversicolor)forests, withB. seminuda being one of the forest trees in suitable habitat.
Most species do not grow well near thecoast, notable exceptions being the southernWestern Australian speciesB. speciosa,B. praemorsa andB. repens. Only a few species, such asB. rosserae andB. elderiana (swordfish banksia), occur inarid areas. Most of the eastern Australian species survive inuplands, but only a few of theWestern Australian species native to theStirling Ranges –B. solandri,B. oreophila,B. brownii andB. montana – survive at high elevations.
Studies of the south-western species have found the distribution ofBanksia species to be primarily constrained by rainfall. With the exception ofB. rosserae, no species tolerates annual rainfall of less than 200 millimetres, despite many species surviving in areas that receive less than 400 millimetres.Banksia species are present throughout the region of suitable rainfall, with greatest speciation in cooler, wetter areas. Hotter, drier regions around the edges of its range tend to have fewer species with larger distributions. The greatest species richness occurs in association with uplands, especially the Stirling Range.[19]
There are many fossils ofBanksia. The oldest of these are fossil pollen between 65 and 59 million years old. There are fossil leaves between 59 and 56 million years old found in southern New South Wales.[20] The oldest fossil cones are between 47.8 and 41.2 million years old, found in Western Australia.[21] AlthoughBanksia is now only native to Australia and New Guinea, there are fossils from New Zealand, between 21 and 25 million years old.[22]
Evolutionary scientists Marcell Cardillo and Renae Pratt have proposed a southwest Australian origin for banksias despite their closest relatives being north Queensland rainforest species.[23]
Banksias are heavy producers ofnectar, making them an important source of food fornectivorous animals, includinghoneyeaters and small mammals such as rodents,antechinus,honey possums,pygmy possums,gliders andbats.[24] Many of these animals play a role in pollination ofBanksia. Various studies have shown mammals and birds to be important pollinators.[25][26] In 1978, Carpenter[27] observed that some banksias had a stronger odour at night, possibly to attract nocturnal mammal pollinators. Other associated fauna include thelarvae ofmoths (such as theDryandra Moth) andweevils, which burrow into the "cones" to eat the seeds andpupate in the follicles; andbirds such ascockatoos, who break off the "cones" to eat both the seeds and theinsect larvae.
A number ofBanksia species are considered rare or endangered. These includeB. brownii (feather-leaved banksia),B. cuneata (matchstick banksia),B. goodii (Good's banksia),B. oligantha (Wagin banksia),B. tricuspis (pine banksia), andB. verticillata (granite banksia).
Banksia plants are naturally adapted to the presence of regularbushfires in the Australian landscape. About half ofBanksia species are killed by bushfire, but these regenerate quickly from seed, as fire also stimulates the opening of seed-bearing follicles and the germination of seed in the ground. The remaining species usually survive bushfire, either by resprouting from a woody base known as alignotuber or, more rarely,epicormic buds protected by thick bark. InWestern Australia, banksias of the first group are known as 'seeders' and the second group as 'sprouters'.[28]
Infrequent bushfires at expected intervals pose no threat, and are in fact beneficial for regeneration ofbanksia populations. However, too frequent bushfires can seriously reduce or even eliminate populations from certain areas, by killing seedlings and young plants before they reach fruiting age.[29] Many fires near urban areas are caused by arson, and thus the frequency is often much higher than fires would have been prior to human habitation. Furthermore, residents who live in areas near bushland may pressure local councils to burn areas near homes more frequently, to reduce fuel-load in the bush and thus reduce ferocity of future fires. Unfortunately there are often discrepancies in agreed frequency between these groups and conservation groups.
Another threat toBanksia is thewater mouldPhytophthora cinnamomi, commonly known as "dieback". Dieback attacks the roots of plants, destroying the structure of the root tissues, "rotting" the root, and preventing the plant from absorbing water and nutrients.Banksia'sproteoid roots, which help it to survive in low-nutrient soils, make it highly susceptible to thisdisease. All Western Australian species are vulnerable, although most eastern species are fairly resistant.[30]
Vulnerable plants typically die within a few years of infection. Insouthwest Western Australia, where dieback infestation is widespread, infested areas ofBanksia forest typically have less than 30% of the cover of uninfested areas. Plant deaths in such large proportions can have a profound influence on the makeup of plant communities. For example, in southwestern AustraliaBanksia often occurs as an understorey to forests ofjarrah (Eucalyptus marginata), another species highly vulnerable to dieback. Infestation kills both the jarrah overstorey and the originalBanksia understorey, and over time these may be replaced by a more open woodland consisting of an overstorey of the resistant marri (Corymbia calophylla), and an understorey of the somewhat resistantBanksia sessilis (parrot bush).[31]
A number of species ofBanksia are threatened by dieback. Nearly every known wild population ofB. brownii shows some signs of dieback infection, which could possibly wipe it out within years.[32][33] Other vulnerable species includeB. cuneata, andB. verticillata.
Dieback is notoriously difficult to treat, although there has been some success withphosphite andphosphorous acid, which are currently used to inoculate wildB. brownii populations. However this is not without potential problems as it alters the soil composition by addingphosphorus. Some evidence suggests that phosphorous acid may inhibit proteoid root formation.[34]
Because dieback thrives in moist soil conditions, it can be a severe problem for banksias that are watered, such as in the cut flower industry and urban gardens.
Most of species are shrubs, only few of them can be found as trees and they are very popular because of their size, the tallest species are:B. integrifolia having its subspeciesB. integrifolia subsp.monticola notable for reaching the biggest size for the genus and it is the most frost tolerant in this genus,B. seminuda,B. littoralis,B. serrata; species that can grow as small trees or big shrubs:B. grandis,B. prionotes,B. marginata,B. coccinea,B. speciosa andB. menziesii. Due to their size these species are popularly planted in parks, gardens and streets, the remaining species in this genus are only shrubs.
Banksias are popular garden plants in Australia because of their large, showy flower heads, and because the large amounts ofnectar they produce attractsbirds and smallmammals. Popular garden species includeB. spinulosa,B. ericifolia,B. aemula (Wallum Banksia ),B. serrata (Saw Banksia),Banksia media (Southern Plains Banksia) and thecultivarBanksia 'Giant Candles'.Banksia species are primarily propagated by seed in the home garden as cuttings can be difficult to strike. However, commercial nurserymen extensively utilize the latter method (indeed, cultivars by nature must be vegetatively propagated by cuttings or grafting).
Over time, dwarf cultivars and prostrate species are becoming more popular as urban gardens grow ever smaller. These include miniature forms under 50 cm high ofB. spinulosa andB. media, as well as prostrate species such asB. petiolaris andB. blechnifolia.
Banksias possibly require more maintenance than other Australian natives, though are fairly hardy if the right conditions are provided (sunny aspect and well drained sandy soil).They may need extra water during dry spells until established, which can take up to two years. If fertilised, only slow-release, low-phosphorusfertilizer should be used, as theproteoid roots may be damaged by highnutrient levels in the soil. All respond well to some form of pruning.
Within the Australian horticultural community there is an active subculture ofBanksia enthusiasts who seek out interesting flower variants, breed and propagate cultivars, exchange materials and undertake research into cultivation problems and challenges. The main forum for exchange of information within this group isASGAP'sBanksia Study Group.[35]
With the exception of thenurseryindustry,Banksia have limited commercial use. Some species, principallyB. coccinea (scarlet banksia),B. baxteri,B. hookeriana (Hooker's banksia),B. sceptrum (sceptre banksia), andB. prionotes (acorn banksia), and less commonlyB. speciosa (showy banksia),B. menziesii (Menzies' banksia),B. burdettii andB. ashbyi are grown on farms in Western and Southern Australia, as well as Israel and Hawaii, and the flower heads harvested for thecut flower trade. Eastern species, such asB. ericifolia,B. robur andB. plagiocarpa, are sometimes cultivated for this purpose.[36] The nectar is also sought bybeekeepers, not for the quality of the dark-colouredhoney, which is often poor, but because the trees provide an abundant and reliable source of nectar at times when other sources provide little.[37]
Banksiawood is reddish in color with an attractive grain but it is rarely used as it warps badly on drying. It is occasionally used for ornamental purposes in wood turning and cabinet paneling. It has also been used to makekeels for smallboats. Historically, the wood of certain species such asB. serrata was used for yokes and boat parts.[38] The large "cones" or seed pods ofB. grandis are used forwoodturning projects. They are also sliced up and sold asdrink coasters; these are generally marketed assouvenirs for internationaltourists. Woodturners throughout the world valueBanksia pods for making ornamental objects.
TheIndigenous people of south-western Australia would suck on the flower spikes to obtain the nectar, they also soaked the flower spikes in water to make a sweet drink.[39][40][41] TheNoongar people of southwest Western Australia also used infusions of the flower spikes to relieve coughs and sore throats.[41] TheGirai wurrung peoples of the western district of Victoria used the spent flower cones to strain water by placing the cones in their mouths and using them like a straw.[42]Banksia trees are a reliable source of insect larvae which are extracted as food.
A number of field guides and other semi-technical books on the genus have been published. These include:
Perhaps the best known cultural reference toBanksia is the "big bad Banksia men" ofMay Gibbs' children's bookSnugglepot and Cuddlepie. Gibb's "Banksia men" are modelled on the appearance of agedBanksia "cones", with follicles for eyes and other facial features. There is some contention over which species actually provided the inspiration for the "Banksia men": the drawings most resemble the old cones ofB. aemula orB. serrata, butB. attenuata (slender banksia) has also been cited, as this was the species that Gibbs saw as a child in Western Australia.[44]
In 1989, theBanksia Environmental Foundation was created to support and recognise people and organizations that make a positive contribution to the environment. The Foundation launched the annual Banksia Environmental Awards in the same year.[45]
Announced in June 2023, the exoplanetWASP-19b was named "Banksia" in the thirdNameExoWorlds competition. The approved name was proposed by a team from Brandon Park Primary School in Wheelers Hill (Melbourne, Australia), led by scientist Lance Kelly and teacher David Maierhofer,[46] after various types ofBanksia plants.[47]
