Australia is one of Earth's twelve mega diverse nations. Its unique plant life, is typified by the uniquely Australian gum tree, distinguishes Australia as one of the world's six floristic regions. Not only is Australia rich in species, but most of its native plants and animals are endemic; that is, they occur naturally only in Australia. Australia's high levels of uniqueness arise because for more than 50 million years, Australia has been an island continent and its fauna and flora has evolved in isolation. Eighty-five percent of Australia's flowering plants, 84 % of mammals, 89 % of reptiles, 93 % of frogs, and 85 % of inshore marine fish are unique to Australia. Even among the highly mobile birds, 45 % of species are confined to Australia.
There are many reasons why Australia is rich in species. Despite an absence of expansive mountain ranges and extensive forests, the continent spans nearly 35 degrees of latitude from 5 degrees in the north to nearly 40 degrees south and has a precipitous rainfall gradient from the moist continental fringes to the arid interior.
These gradients from the tropics to the cool temperate zones and from the wet to the dry produce a succession of communities, each with its distinctive and highly adapted flora and fauna. The long stability of the continent has also been important in the evolution of a diverse fauna and flora and the continent's richest plant communities are found in the southwest of Western Australia and in the east on the sandstones enveloping Sydney. Both regions have a long history of stability and have not been glaciated or covered by the oceans for tens of millions of years.
The origin of some flora can be traced back to the Pangaean times For example, the fossil kauri pine Agathis jurassica...