The Australasian grass flora in a global context

Australia's flora and fauna have long been considered unique, but whether this applies to its grasses is less known. This study characterises the Australasian grass flora biogeographically. We investigate the distribution of C3 and C4 grass genera across four continents and construct broad profiles of their grass flora. We use endemism to examine global patterns of specialisation, and inter-continental distributions as indicators of dispersal, using databases constructed over twenty years. We examined Australasian patterns with regard to endemicity and shared groups and categorised all of the region's genera into four age classes, from Australia's separation from Gondwana to the present. Globally, each continent presented a unique profile and C4 grasses were more widely shared than C3. Australasia's grasses equally comprise C3 and C4 genera; it shared two thirds of its C4 types with other continents, whereas C3 types split evenly between shared and endemic. Australasia shared relatively few genera with just one neighbour (7% C3, 13% C4), primarily with EurAsia. Australasian grass genera and species were either endemic or globally widespread, and 88% of C3 and 93% of C4 species were derived from lineages that originated elsewhere. We conclude Southeast Asia was the gateway for dispersal into Australasia, akin to rainforest taxa exchanges which increased from c12 Ma, with about 65% of Australasia's grass genera arriving in the past 3.5 Ma. The strong presence of C4 grasses in Australasia implies they have infiltrated a wide range of ecosystems, many probably occupied by ancient taxa with which they had not co-evolved.