Southern Hemisphere Mesozoic and Tertiary Podocarpaceae and Fagaceae and their palaeogeographic significance

Abstract The present botanical affinities between Australasia (taken to include Australia, Tasmania, New Zealand, New Guinea and New Caledonia) and South America have long been a favourite subject of discussions between botanists and geologists. Following Dawson (1958) the affinities can perhaps be best summarized by comparing the floras of the geographic extremes, New Guinea and southern South America, with that of an intermediate area, New Zealand. Approximately 140 genera of seed plants are found in two or in all three of these areas. Of these, some 60 genera have a cosmopolitan distribution so that their presence does not imply any special relationship. The remaining 80 genera are largely restricted to Australasia and South America. About 30 of these genera are found in New Guinea and New Zealand but not in South America; some 25 are found in New Zealand and South America only and approximately 25 are found in all three areas. How can these links between the floras of these widely separated areas be best explained? Both Florin (1940) in his classic paper on the Tertiary coniferg of the southern hemisphere and Dawson (1958) have rightly commented that the solution to this phytogeographical problem must be looked for mainly in the Mesozoic and Tertiary floras of Australasia, South America and Antarctica.