The distribution of Australian relict plants and its bearing on angiosperm evolution

Abstract

The distribution of relict plants in the Australian flora shows a bimodal distribution of genera with relict vegetative characters and a unimodal distribution centred on N.E. Queensland for floral characters. Archaic features of the vegetative group link them with the Glossopteridae of Permian age. The geophysical history of the continent is reviewed and indicates only minor climatic changes since the Permian, which would permit the survival of primitive vegetative features. The bimodal distribution of this group is accounted for by the Cretaceous marine invasion of the continent and the unimodal distribution of the floral relicts by a preponderance of genera of Indo-Malaysian affinity, which could not have entered Australia until contact was made with New Guinea about 45 m. y. B.P. Two different cycles of evolutionary diversification are responsible for the two elements. Vegetative features of the Proteaceae relate to the Glossopteridae and are supported by Permian fossils scarcely distinguishable from modern leaves of Epacridaceae. If recent discoveries of Glossopteris fructifications are accepted as pro-angiosperms, it is shown that some anomalies in the vascular supply to the androecium in the Proteaceae can be accounted for.