Australia broke off from the supercontinent Pangaeamore than fifty million years ago, and the species of plants living at that time continued to change and adapt to conditions on the isolated island. This led to distinctive plants, differing from those of the interconnected Eurasian-African-American landmass, where new immigrant species changed the ecology.
Many species of plants in Australia are found nowhere else on earth, except where they have been introduced by humans. Such species are known as endemic species. This distinctiveness is the result of the long isolation of the Australian continent from other landmasses.
Australian vegetation is dominated by two types of plants—the eucalyptus and the acacia. There are 569 known species of eucalypts and 772 species of acacia. Nevertheless, a great deal of botanical diversity exists throughout this large continent.
Climate and Ecology
Climate is a major influence on Australian flora, and the most striking feature of the Australian environment as a whole is its aridity. Nutrient-poor soils affect the nature of Australia’s vegetation, especially in arid areas.
Half of the continent receives less than 11.8 inches (300 millimeters) of rainfall per year; small parts of Australia receive annual rainfall of 75 inches (800 millimeters). Therefore, forests cover only a small percentage of Australia.
A close correlation exists between rainfall and vegetation type throughout Australia. Small regions of tropical rain forest grow in mountainous areas of the northeast, in Queensland. In the cooler mountains of New South Wales, Victoria, and Tasmania, extensive temperate rain forests thrive.
More extensive than rain forest, however, is a more open forest known as sclerophyllous forest, which grows in the southern part of the Eastern Highlands in New South Wales and Victoria, in most of Tasmania, and in southwest Western Australia.
A huge crescent-shaped region of woodland vegetation, an open forest of trees of varying height, with an open canopy, extends throughout northern Australia, the eastern half of Queensland and the inland plains of New South Wales, and to the north of the Western Australian sclerophyllous forest.
Beyond this region, the climate is arid, and shrubs, forbs (smaller herbaceous plants), and grasses predominate. The tropical north of inland Queensland,Northern Territory, and a smaller part of Western Australia have extensive areas of grassland.
Much of Western Australia and South Australia, as well as interior parts of New South Wales and Queensland, are shrubland, where grasses and small trees grow sparsely. In the center of the continent is the desert, which has little vegetation, except along watercourses.
In 1688 the explorer William Dampier noticed kino coming from trees in Western Australia and called it "gum dragon", as he thought it was the same as commercial resin. Kino is technically not gum, as it is not water-soluble.
The scientific name Eucalyptuswas chosen by the first botanist to study the dried leaves and flowers of a tree collected in Tasmania during Captain James Cook's third voyage in 1777. The French botanist chose the Greek name because he thought that the bud with its cap (operculum) made the flower "well" (eu) "covered" (kalyptos). The hard cases are commonly called gum nuts.
The more than five hundred species of eucalypts in Australia range from tropical species in the north to alpine species in the southern mountains. Rain-fall, temperature, and soil type determine which particular eucalyptwill be found in any area. Eucalyptus trees dominate the Australian forests of the east and south, while smaller species of eucalyptus grow in the drier woodland or shrubland areas.
It is easier to mention parts of Australia where euca- lypts do not grow: the icy peaks of the Australian Alps, the interior deserts, the Nullarbor Plain, and the tropical and temperate rain forests of the East- ern Highlands.
The scientific classification of the eucalypts proved difficult to European botanists. Various experts used flowers, leaves, or other criteria in their attempts to arrange the different species into a meaningful and useful taxonomy, or classification scheme. George Bentham eventually chose the shape of the anthers—the part of the stamen that holds the pollen—together with fruit, flowers, and nuts.
A simpler classification of the eucalypts, commonly used by foresters, gardeners, and naturalists, arranges them into six groups based on their bark: gums have smooth bark, which is sometimes shed; bloodwoods have rough, flaky bark; iron barks have very hard bark with deep furrows between large pieces; stringy barks have fibrous bark that can be peeled off in long strips; peppermints have mixed but loose bark; boxes have furrowed bark, firmly attached. This system was devised in 1859 by Ferdinand von Müller, the first government botanist of the Colony of Victoria and the father of Australian botany.
Many of the native plants of Australia, along with eucalypts, show typical adaptations to the arid climate, such as deep taproots that can reach down to the water table. Another common feature is small, shiny leaves, which reduce transpiration.
Eucalyptus leaves are tough or leathery and are described as sclerophyllous. Sclerophyllous forests of eucalypts cover the wetter parts of Australia, the Eastern Highlands, or Great Dividing Range, and the southwest of Western Australia.
The hardwood from these forests is generally not of a quality suitable for building, so areas are cleared and the trees made into wood chips that are exported for manufacture of newsprint paper. This has been a controversial use of Australian forests, especially where the native forest has been cleared and replaced with pine plantations.
The southwest corner of Western Australia has magnificent forests featuring two exceptional species with Aboriginal names, karri and jarrah. Karri is one of the world’s tallest trees, growing to 295 feet (90 meters) tall. This excellent hardwood tree is widely used for construction.
The long, straight trunks are covered in smooth bark that is shed each year, making a colorful display of pink and gray. These forests are now protected. Jarrah grows to 120 feet (40meters) in height and is a heavy, durable timber. It was used for road construction in the nineteenth century, but now the deep red timber is prized for furniture, flooring, and paneling.
During the nineteenth century, Australia could also claim to be home to the world’s tallest trees, the mountain ash. The tallest tree, which observers claimed was 433 feet (132 meters) high and with the top broken away,was felled in 1872. The tallest accurately measured tree was 374 feet (114 meters) high.
The most widely distributed of all Australian eucalypts is the beautiful river red gum. These trees grow along riverbanks and watercourses throughout Australia, especially in inland areas; their spreading branches provide wide shade and habitat formany animals.
Koalas eat leaves from this tree. In the song "Waltzing Matilda", Australia's unofficial national anthem, aman camps "under the shade of a coolabah tree". This word might apply to any eucalypt, but it is most likely a river red gum.
In drier interior areas and in some mountain areas, there are more than one hundred smaller species of eucalypts that are known by the Aboriginal name mallee. These many-trunked shrubs have underground lignotubers, roots that storewater.
Much of this marginal country was cleared for farming, creating a situation similar to that of the 1930’s Dust Bowl in the United States. In the dry Australian summers bushfires are a great danger in themallee and in any eucalyptus forest. The volatile oils of the eucalyptus trees can lead to rapid spread in the tree crowns, jumping across human-made firebreaks.
On the other hand, several Australian trees not only can survive fires but actually require fire for their seeds to germinate. Eucalypts have been introduced to many countries, including Italy, Egypt, Ethiopia, India, China, and Brazil, and they are common in California, where they have been growing as introduced trees for 150 years.
Wattles frequently have masses of colorful flowers, usually bright yellow. One species is the national flower of Australia. Other interesting acacias include the mulga, which has an attractive wood.
Although rain-forest vegetation covers only a small area of Australia, it is exceptionally varied and of great scientific interest. Neither of the two general types of rain forest found in Australia has eucalypts. Rain forests are located along the Eastern Highlands, or Great Dividing Range, where rainfall is heavy.
In small areas of tropical Queensland, where rainfall is also heavy, true tropical rain forest is found. The flora are similar to those in Indonesian and Malaysian rain forests. The tropical rain forest contains thousands of species of trees, as well as lianas, lawyer vine, and the fierce stinging tree,whose touch could kill an unwary explorer.
Toward the north of New South Wales, a kind of subtropical to temperate rain forest grows. Cool, wet Victoria and Tasmania have extensive areas of temperate rain forest, where only a few species dominate the forests.Arctic beech trees are found, aswell as sassafras and tall tree ferns.
This is the typical Australian bush, which grows close to the coast of New South Wales, Victoria, and Tasmania. The bright Australian sun streams down through the sparse crowns and narrow leaves of the eucalypts. As the climate becomes drier, farther inland from the coast, the open forest slowly changes to a shrubbier woodland vegetation.
Moving farther inland, to still drier regions, woodlands giveway to grasslands, where cattle are raised for beef in the tropics, and sheep are raised for wool in the temperate areas. Before Europeans came to Australia, therewere native grasslands in the interior—tropical grasslands in themonsoonal north, and temperate grasslands in the south and south-west.
Kangaroo grass and wallaby grass once grew in the temperate interior of New South Wales, but much of this has been cleared for agriculture, especially for wheat farming. Mitchell grass is another tussock grass, which grows in western Queensland and into the Northern Territory. Cattle and sheep graze extensively on this excellent native pasture.
The most common grassland type in Australia is dominated by spinifex, a spiky grass that grows in clumps in the arid interior and west. Even cattle cannot feed on spinifex grass, so this ecosystem is less threatened than most other grasslands. The northern grasslands are dotted with tall red termite mounds; those that are aligned north-south for protection from the hot sun are built by so-called magnetic termites.
Other Trees and Plants
Many people think that macadamia nuts are native to Hawaii, which produces 90 percent of the world’s crop, but in fact, the tree is native to Australia. It was discovered by Ferdinand von Müller in 1857 on an expedition in northern Australia. Müller named the tree after his Scottish friend, John Macadam. The trees were introduced to Hawaii in 1882.
Cycads are plants from an ancient species which still thrive in Australia. The Macrozamia of North Queensland is a giant fernlike plant. Similarly old are the Xanthorrhea grass-trees, which used to be called "blackboys". A single spearlike stem rises from a delicate green skirt on this fire-resistant species.
In northwest Australia, the baobab, or bottle tree, can be found. This fattrunked tree collects water in its tissue. One is said to have served as a temporary prison. The only other baobabs are found in Africa, a reminder that these continents were once joined. Bottlebrush is an Australian shrub with colorful flowers that has become popular with gardeners in many parts of the world.
Extinct and Endangered Plants
Human activities in Australia have led to the extinction of more than eighty species of plants, and the list of endangered plants contains more than two hundred species. Many nonnative species have been introduced to Australia by Europeans.
Some have become pests, such as the blackberry in Victoria, the lantana in north Queensland, and water hyacinth, found throughout the continent. There are 462 national parks in Australia, as well as other conservation areas, where native flora are protected.
Aboriginal Plant Use
The Australian Aborigines used plants as sources of food and for medicinal purposes. Food plants included nuts, seeds, berries, roots, and tubers. Nectar from flowering plants, the pithy center of tree ferns, and stems and roots of reeds were eaten.
Fibrous plants were made into string for weaving nets or making baskets. Weapons such as spears, clubs, and shields, as well as boomerangs, were made from hardwoods such as eucalyptus. The bunya pine forests of southeast Queensland were a place of great feasting when the rich bunya nuts fell.