Distribution and Habitat
All but one of the living Banksia species are endemic to Australia. The exception is B. dentata (Tropical Banksia), which occurs throughout northern Australia, and on islands to the north including New Guinea and the Aru Islands. An extinct species, B. novae-zelandiae, was found in New Zealand. The other species occur in two distinct geographical regions: southwest Western Australia and eastern Australia. Southwest Western Australia is the main centre of biodiversity; over 90% of all Banksia species occur only there, from Exmouth in the north, south and east to beyond Esperance on the south coast. Eastern Australia has far fewer species, but these include some of best known and most widely distributed species, including B. integrifolia (Coast Banksia) and B. spinulosa (Hairpin Banksia). Here they occur from the Eyre Peninsula in South Australia right around the east coast up to Cape York in Queensland.
The vast majority of Banksia are found in sandy or gravelly soils, though some populations of B. marginata (Silver Banksia) and B. spinulosa do occur on heavier, more clay-like, soils. B. seminuda is exceptional for its preference for rich loams along watercourses.
Most occur in heathlands or low woodlands; of the eastern species, B. integrifolia and B. marginata occur in forests; many south-western species such as B. grandis, B. sphaerocarpa, B. sessilis, B. nobilis and B. dallanneyi grow as understorey plants in Jarrah (Eucalyptus marginata), Wandoo (E. wandoo) and Karri (E. diversicolor) forests, with B. seminuda being one of the forest trees in suitable habitat.
Most species do not grow well near the coast, notable exceptions being the southern Western Australian species B. speciosa, B. praemorsa and B. repens. Only a few species, such as B. rosserae and B. elderiana (Swordfish Banksia), occur in arid areas. Most of the eastern Australian species survive in uplands, but only a few of the Western Australian species native to the Stirling Ranges - B. solandri, B. oreophila, B. brownii and B. montana - survive at high altitudes.
Studies of the south-western species have found the distribution of Banksia species to be primarily constrained by rainfall. With the exception of B. 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 the genus' range tend to have fewer species with larger distributions. The greatest species richness occurs in association with uplands, especially the Stirling Range.
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