The arrival of humans around 50,000 years ago[2][3] and the settlement by Europeans from 1788, has had a significant impact on the flora. The use of fire-stick farming by Aboriginal people led to significant changes in the distribution of plant species over time, and the large-scale modification or destruction of vegetation for agriculture and urban development since 1788 has altered the composition of most terrestrial ecosystems, leading to the extinction of 61 plant species by 2006, and endangering over 1000 more.
Origins and history
The Tasmanian rainforest is considered a Gondwanan relic.
Australia was part of the southern supercontinent Gondwana, which also included South America, Africa, India and Antarctica. Most of the modern Australian flora had their origin in Gondwana during the Cretaceous when Australia was covered in subtropical rainforest. Australian ferns and gymnosperms bear a strong resemblance to their Gondwanan ancestors,[4] and prominent members of the early Gondwanan angiosperm flora such as the Nothofagus, Myrtaceae and Proteaceae were also present in Australia.[5]
Gondwana began to break up 140 million years ago (MYA); 50 MYA during the Eocene Australia separated from Antarctica, and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene era 5.3 MYA. As Australia drifted, local and global climatic change had a significant and lasting effect: a circumpolar oceanic current developed, atmospheric circulation increased as Australia moved away from Antarctica, precipitation fell, there was a slow warming of the continent and arid conditions started to develop.[6] These conditions of geographic isolation and aridity led to the development of a more complex flora. From 25 to 10 MYA pollen records suggest the rapid radiation of species like Eucalyptus, Casuarina, Allocasuarina, Banksia and the pea-flowered legumes, and the development of open forest; grasslands started to develop from the Eocene. Collision with the Eurasian Plate also led to additional South-east Asian and cosmopolitan elements entering the flora like the Lepidium and Chenopodioideae.[7]
The development of aridity and the old and nutrient poor soils of the continent led to some unique adaptations in the Australian flora and evolutionary radiation of genera – like Acacia and Eucalyptus – that adapted to those conditions. Hard leaves with a thick outer layer, a condition known as scleromorphy, and C4 and CAM carbon fixation which reduce water loss during photosynthesis are two common adaptations in Australian arid-adapted dicot and monocot species respectively.
Rising aridity also increased the frequency of fires in Australia. Fire is thought to have played a role in the development and distribution of fire-adapted species from the Late Pleistocene. An increase in charcoal in sediment around 38,000 years ago coincides with dates for the inhabitation of Australia by the Indigenous Australians and suggests that man-made fires, from practices like fire-stick farming, have played an important role in the establishment and maintenance of sclerophyll forest, especially on the east coast of Australia.[8] Adaptations to fire include lignotubers and epicormic buds in Eucalyptus and Banksia species that allow fast regeneration following fire. Some genera also exhibit serotiny, the release of seed only in response to heat and/or smoke. Xanthorrhoea grass trees and some species of orchids only flower after fire.[9]
Biogeography
In biogeography and zoogeography, Australia alone is sometimes considered a realm (Australian realm), while some authors unite the area with other regions to form the Australasian realm.
Major vegetation groups in Australia from the 2009 Atlas of Australian ResourcesHummock grassland, the green hummocks are Triodia pungens and the blue-grey hummocks are Triodia basedowii.
Australia's terrestrial flora can be collected into characteristic vegetation groups. The most important determinant is rainfall, followed by temperature which affects water availability.[12] Several schemes of varying complexity have been created. As of 2022, the NVIS (National Vegetation Information System) divides Australia's terrestrial flora into 33 Major Vegetation Groups,[13] and 85 Major Vegetation Subgroups.[14]
According to the scheme the most common vegetation types are those that are adapted to arid conditions where the area has not been significantly reduced by human activities such as land clearing for agriculture. The dominant vegetation type in Australia is the hummock grasslands that occur extensively in arid Western Australia, South Australia and the Northern Territory. It accounts for 23% of the native vegetation, the predominant species of which are from the genus Triodia. Zygochloa also occurs in inland sandy areas like the Simpson Desert.
A further 39% of native vegetation is covered by a combination of:
Eucalypt woodlands found at the transition between hummock grasslands and higher rainfall areas where conditions still limit tree growth; the woodland may have a grass or shrubby understory. The largest area is in Queensland.
Acacia forests and woodlands that occur in semi-arid areas where tree growth is stunted.[15] The dominant Acacia species varies with the location, and may include lancewood, bendee, mulga, gidgee and brigalow. The largest area is in Western Australia.[16]
Acacia shrublands in semi arid and arid regions. The most common are mulga shrublands; the largest area is in Western Australia.
Tussock grasslands that occur in semi-arid and some temperate [clarification needed] parts of Australia; they host a large variety of grasses from more than 10 genera. The largest area is in Queensland.
Chenopod/samphire shrubs and forblands that are widespread in the near-estuarine, arid and semi-arid areas. Species in chenopod communities are drought and salt tolerant and include the genera Sclerolaena, Atriplex, Maireana, Chenopodium and Rhagodia while samphire representatives include Tecticornia, Salicornia, Sclerostegia and Sarcocornia. Both South and Western Australia have large areas with this vegetation type.
Other groups with restricted areas of less than 70,000 square kilometres include tropical or temperate rainforest and vine thickets, tall or open eucalypt forests, Callitris and Casuarina forests, and woodlands and heath.
Vascular plants
Australia has over 21,077 described species of vascular plants,[17] these include the angiosperms, seed-bearing non-angiosperms (like the conifers and cycads), and the spore-bearing ferns and fern allies.[18] Of these about 11% are naturalised species; the remainder are native or endemic.[19] The vascular plant flora has been extensively catalogued, the work being published in the ongoing Flora of Australia series. A list of vascular plant families represented in Australia using the Cronquist system is also available.[20]
At the higher taxonomic levels the Australian flora is similar to that of the rest of the world; most vascular plant families are represented within the native flora, with the exception of the cacti, birch and a few others, while 9 families occur only in Australia.[21][22] Australia's vascular flora is estimated to be 85% endemic;[23] this high level of vascular plant endemism is largely attributable to the radiation of some families like the Proteaceae, Myrtaceae, and Fabaceae.
Data from Orchard modified to AGPII classifications.[18]
The native Australian flora contains many monocotyledons. The family with the most species is the Poaceae which includes a huge variety of species, from the tropical bamboo Bambusa arnhemica to the ubiquitous spinifex that thrives in arid Australia from the genus Triodia. There are more than 800 described species of orchid in Australia.[24] About one quarter of these are epiphytes. The terrestrial orchids occur across most of Australia, the majority of species being deciduous – their aboveground parts die back during the dry season and they re-sprout from a tuber when it rains.
Other families with well-known representatives include the alpine Tasmanian button grass, which form tussock-like mounds from the Cyperaceae; the genus Patersonia of temperate iris-like forbs from the Iridaceae; and, the kangaroo paws from the family Haemodoraceae. The Xanthorrhoea grass trees, the screw palms of the Pandanaceae and palms are large monocots present in Australia. There are about 57 native palms; 79% of these only occur in Australia.[25]
Many plant families that occur in Australia are known for their floral displays that follow seasonal rains. The Asteraceae is well represented by its subfamily Gnaphalieae, which included the paper or everlasting daisies; this group has its greatest diversity in Australia. Other families with flowering shrubs include the Rutaceae, with the fragrant Boronia and Eriostemon, the Myoporaceae with the Eremophila, and members of the Ericaceae with Victoria's Floral Emblem Epacris impressa.
Senna odorata, a fabaceae native to eastern Australia
Australia's salt marshes and wetlands are covered by a large variety of salt and drought tolerant species from the Amaranthaceae which include the saltbushes (Atriplex) and bluebushes (Maireana and Chenopodium). Many of these plants have succulent leaves; other native succulents are from the genera Carpobrotus, Calandrinia and Portulaca. Succulent stems are present in many of the Euphorbiaceae in Australia, though the best known members are the non-succulent looking fragrant Wedding bushes of the genus Ricinocarpos. Carnivorous plants which favour damp habitats are represented by four families including the sundews, bladderworts, pitcher-plants from the Cephalotaceae, which are endemic to Western Australia, and the Nepenthaceae.
Aquatic monocots and dicots both occur in Australian waters. Australia has about 51,000 square kilometres of seagrass meadows and the most diverse group seagrass species in the world. There are 22 species found in temperate waters and 15 in tropical waters out of a known 70 species worldwide.[26] Aquatic dicots include the mangroves; in Australia there are 39 mangrove species that cover 11,500 square kilometres and comprise the third largest area of mangroves in the world.[27] Other native aquatic dicots here include water lilies and water milfoils.
Gymnosperms
Gymnosperms present in Australia include the cycads and conifers. There are 69 species of cycad from 4 genera and 3 families of eastern and northern Australia, with a few in south-western Western Australia and central Australia[clarification needed]. Native conifers are distributed across 3 taxonomic families (Cupressaceae, Podocarpaceae, Araucariaceae), 14 genera and 43 species, of which 39 are endemic. Most species are present in wetter mountainous areas consistent with their Gondwanan origins, including the genera Athrotaxis, Actinostrobus, Microcachrys, Microstrobos, Diselma and the Tasmanian Huon pine, sole member of the genus Lagarostrobos. Callitris is a notable exception; species from this genus are found mainly in drier open woodlands.[28] The most recently discovered species of conifer is the living fossilWollemi pine, which was first described in 1994. Although many Australian conifers are referred to as 'pines', there are no members of the pine family (Pinaceae) native to Australia.
Ferns and fern allies
Spore bearing vascular plants include the ferns and fern allies. True ferns are found over most of the country and are most abundant in tropical and subtropical areas with high rainfall. Australia has a native flora of 30 families, 103 genera and 390 species of ferns, with another 10 species being naturalised. The "fern allies" are represented by 44 native species of whisk ferns, horsetails and lycophytes.[28] Ferns prefer a cool and damp environment since water is required for reproduction, the majority of Australian species are found in bushland [clarification needed] and rainforest, there are aquatic, epiphytic (Platycerium, Huperzia and Asplenium), and terrestrial species including large tree ferns from the genera Cyathea and Dicksonia.
Non-vascular plants
The algae are a large and diverse group of photosynthetic organisms. Many studies of algae include the cyanobacteria, in addition to micro and macro eukaryotic types that inhabit both fresh and saltwater. Currently, about 10,000 to 12,000 species of algae are known for Australia.[29] The algal flora of Australia is unevenly documented: northern Australia remains largely uncollected for seaweeds and marine phytoplankton, descriptions of freshwater algae are patchy, and the collection of terrestrial algae has been almost completely neglected.[30]
The bryophytes – mosses, liverworts and hornworts – are primitive, usually terrestrial, plants that inhabit the tropics, cool-temperate regions and montane areas; there are some specialised members that are adapted to semi-arid and arid Australia. There are slightly fewer that 1,000 recognised species of moss in Australia. The five largest genera are the Fissidens, Bryum, Campylopus, Macromitrium and Andreaea.[31] There are also over 800 species of liver- and horn-worts in 148 genera in Australia.[32]
The fungal flora of Australia is not well characterised; Australia is estimated to have about 250,000 fungal species of which roughly 5% have been described. Knowledge of distribution, substrates and habitats is poor for most species, with the exception of common plant pathogens.[33]
Lichens
Lichens are composite organisms comprising, in most cases, an Ascomycete fungus and a unicellular green alga, their classification is based on the type of fungi. The lichen flora of Australia and its island territories, including Christmas Island, Heard Island, Macquarie Island and Norfolk Island, currently comprises 3,238 species and infra-specific taxa in 422 genera, 34% of which are considered to be endemic.[34]
The first Australian plants recognised and classified in Linnaean taxonomy were a species of Acacia and Synaphea in 1768 as Adiantum truncatum and Polypodium spinulosum respectively by Dutch philologist Pieter Burman the Younger, who stated they were from Java. Later, both were found to be from Western Australia, likely to have been collected near the Swan River, possibly on a 1697 visit there of fellow Dutchman Willem de Vlamingh.[35] This was followed by Cook's expedition making landfall at what is now Botany Bay in April 1770, and the early work of Banks, Solander and Parkinson.[who?] Botanical exploration was enabled by the
founding of the permanent colony at Port Jackson in 1788, and the subsequent expeditions along Australia's coastline.[35]
The Australian flora was utilised by the Indigenous inhabitants of Australia. Indigenous Australians used thousands of species for food, medicine, shelter, tools and weapons.[36] For example, the starchy roots of Clematis microphylla were used in western Victoria to make a dough that was baked, and the leaves of the plant were used as a poultice applied to skin irritations and blisters.[37]
Modification of the Australian environment by Indigenous Australians and following European settlement has affected the extent and the distribution of the flora.
Threats
The changes since 1788 have been rapid and significant: displacement of Indigenous Australians disrupted fire régimes that had been in place for thousands of years; forestry practices have modified the structure of native forests; wetlands have been filled in; and broad scale land-clearing for crops, grazing and urban development has reduced native vegetation cover and led to landscape salinisation, increased sediment, nutrient and salt loads in rivers and streams, loss of habitat and a decline in biodiversity.[40] The intentional and unintentional release of invasive plant and animal species into delicate ecosystems is a major threat to floral biodiversity; 20 introduced species have been declared Weeds of National Significance.[41]
Threatened plant biodiversity
As of 2006, 61 plant species were known to have become extinct since European settlement; and a further 1,239 species were considered threatened.[42]
Protected areas
Protected areas have been created in every state and territory to protect and preserve the country's unique ecosystems. These protected areas include national parks and other reserves, as well as 64 wetlands registered under the Ramsar Convention and 16 World Heritage Sites. As of 2002, 10.8% (774,619.51 km2) of the total land area of Australia is within protected areas.[43] Protected marine zones have been created in many areas to preserve marine biodiversity; as of 2002, these areas cover about 7% (646,000 km2) of Australia's marine jurisdiction.[44]
Biodiversity hotspots
In 2003, the Australian Government's Threatened Species Scientific Committee identified 15 biodiversity hotspots in Australian and 85 characteristic ecosystems, as classified by the Interim Biogeographic Regionalisation for Australia. Some effort is being made to ensure each is represented within a protected area under Australia's Biodiversity Action Plan.[45][46]
^Josephine Flood (2004) Archaeology of the Dreamtime, J.B Publishing, Marleston p. 283 ISBN1-876622-50-4
^Page, C. N. and Clifford, H. T. 1981. Ecological biogeography of Australian conifers and ferns. In A. Keast Ecological Biogeography of Australia. W. Junk
^Dettmann, M. E.; Jarzen, D. M. (1990). "The Antarctic/Australian rift valley: Late Cretaceous cradle of Northeastern Australasian relicts?". Review of Palaeobotany and Palynology. 65 (1–4): 131–144. doi:10.1016/0034-6667(90)90064-p.
^Bowler, J. M. 1982. Age, origin and landform expression of aridity in Australia. In W. R. Barker, P. J. M. Greensdale. Evolution of the Flora and Fauna of Australia. Australian Systematic Botany Society ISBN0-909209-62-6
^Singh, G. et al. 1981. Quaternary vegetation and fire history in Australia. In A. M. Gill, R. A. Groves and I. R. Nobel. Fire and the Australian Biota. Australian Academy of Science, 23-54
^Gill, A. M. 1981. Adaptive responses of Australian vascular plant species to fire. In A. M. Gill, R. H. Groves, and I. R. Noble. eds. Fire and the Australian Biota. Australian Academy of Science
^Тахтаджян А. Л. Флористические области Земли / Академия наук СССР. Ботанический институт им. В. Л. Комарова. — Л.: Наука, Ленинградское отделение, 1978. — 247 с. — 4000 экз. DjVu, Google Books.
^Takhtajan, A. (1986). Floristic Regions of the World. (translated by T.J. Crovello & A. Cronquist). University of California Press, Berkeley, PDF, DjVu.
^Groves, R. H. 1999. Present vegetation types. In A. E. Orchard, ed. Flora of Australia - Volume 1, 2nd edition pp 369-401. ABRS/CSIRO
^Crisp, M. D., West, J. G., and Linder, H.P. 1999. Biogeography of the Australian flora. In A. E. Orchard, ed. Flora of Australia - Volume 1, 2nd edition pp 321-367. ABRS/CSIRO
^ESD Working Group on Biological Diversity. 1991. The Conservation of Biological Diversity as it Relates to Ecologically Sustainable Development, Report of Working Party to the Ecologically Sustainable Development Secretariat, Canberra.
^May, T. W. (2001). "Documenting the fungal biodiversity of Australasia: from 1800 to 2000 and beyond". Australian Systematic Botany. 14 (3): 329–356. doi:10.1071/sb00013.
^ abGeorge, A. S. (1981). "The genus Banksia L.f. — a case history in Australian botany". History in the service of systematics : papers from the Conference to celebrate the centenary of the British Museum Natural History. London: Society for the Bibliography of Natural History. pp. 53–59. ISBN978-0-901843-05-0.
^Traditional uses of the Australian flora have been written on extensively, for an overview see Isaacs, J. 2002 Bushfood: Aboriginal food and herbal medicine. New Holland ISBN1-86436-816-0
^Power, J., Macadamia Power in a Nutshell, 1982, ISBN0-9592892-0-8, p. 13.
^O'Neill, G (1996). "Winning back the macadamia". Ecos. 88: 15–19.
^Williams J. 2000, Managing the Bush: Recent research findings from the EA/LWRRDC National Remnant Vegetation R&D Program, National Research and Development Program on Rehabilitation, Management and Conservation of Remnant Vegetation, Research Report 4/00.
