Recent evidence for autochthony of Australian tropical and subtropical rainforest floristic elements.

Abstract

Studies in continental drift suggest that much of the Australian flora is of Gondwanic origin. The fossil record shows 'Indo-Malesian' and 'Antarctic' elements of the Australian flora were present in southern Australia before a land bridge with South-East Asia was possible, and before Australia and Antarctica were separated. Today there is a remarkable concentration and variety of families of primitive angiosperms in the rainforests of north-eastern Australia. A recent floristic classification of Australian rainforests revealed patterns of outliers and disjunct and relict species assemblages interpretable by past environmental sifting. The existince of refugia is postulated under certain ecological conditions. The proportion of tree genera, shared between homologous habitats in Australia and the Indo-Malesian region suggests common ancestry. Interspersion of rainforest and sclerophyll floras supports the theory that rainforest elements are authochthonous and archetypal, and sclerophylls largely derivative. The use of the terms 'Indo-Malesian' and 'Antarctic' to indicate sources of intrusive floral immigrants should accordingly be discontinued. Thus, tropical or megatherm rainforest and monsoon forest floristic elements should be added to the subtropical (mesotherm) and temperate (microtherm) elements already recognized as remnants of the ancient Gondwanan flora that once covered Australia.-from Authors