The plant family Proteaceae is familiar to nearly all Australians because it includes Banksia, Grevillea, Macadamia, the waratahs and many other common, eye-catching native trees and shrubs.
The Proteaceae family is almost entirely restricted to the continental landmasses of the southern hemisphere. Australia has more species than any other country.
Each country in the Southern Hemisphere has many endemic species of Proteaceae, yet all these species are related. This is because all these countries were once part of the one landmass, Gondwana, until about 100 million years ago. After the separation of Gondwana, species were isolated on different landmasses where they continued to evolve independently of each other, developing their own characteristics and, in many cases, diversifying into numerous different species. For example, the macadamias and their closest relatives are endemic to Australia, but they also have close relatives, which are different species of the same family, in Sulawesi (also Macadamia), South Africa (Brabejum) and tropical South America (Panopsis).
There are other reasons why species in the Proteaceae family are endemic. Firstly, they do not produce the type of seeds that can be carried on the plumage of migratory birds or blown across ocean gaps.
There are also patterns of endemism evident within Australia. Increasing aridity and sea level changes that occurred during the early Tertiary Period, between 12 and 5 million years ago, effectively divided the flora of Australia between east and west. Species that had been widespread across Australia became restricted to non-arid refuges in the south, west and east. The isolated remnants then evolved independently of each other, becoming distinct species.
The tropical rainforests of Queensland are also home to quite a few endemic species of Proteaceae, but these show a different pattern of relationships. Instead of having close relatives elsewhere in Australia, some of these have no close relatives in Australia at all. These species are relics of groups that were more widespread when rainforests covered much of Australia more than 15 million years ago. The gradual drying of the continent over the last few million years has reduced the habitats of these species to a small refuge in the wettest part of Australia.
Dr Peter Weston
Royal Botanic Gardens Sydney
Copyright © Australian Museum, 2003
This page: http://www.amonline.net.au/factsheets/proteaceae.htm
