Evolution of the eucalypts – an interpretation from the macrofossil record

Abstract

Eucalypts have influenced the fire ecology of the Australian landscape more than any other plant group. They are the iconic plant taxon in the Australian vegetation today, but their origin, early evolution and migration remain poorly understood, mostly because of a remarkably sparse and underworked fossil record. However, a recent major macrofossil find in southern South America, coupled with increasing sophistication of molecular phylogenetic and palynological research allow for a more comprehensive summary of the likely early history of this group of genera. It is likely that the origin was close to the Cretaceous–Paleogene boundary, somewhere in the Weddellian Biogeographic Province (which includes southern South America, western Antarctica and south-eastern Australia), in an area with high natural fire frequency. Evidence for the early record of eucalypts in Australia and their eventual spread across the continent, leading to their current dominance of the Australian plant biomass is growing and is consistent with a drying climate and increasing fire frequency following a very wet period during the Paleogene. The causes of the extinction of eucalypts from South America and probably New Zealand are considered, but remain obscure.