Australia’s Acacia: unrecognised convergent evolution

This chapter takes a slightly different, long-term, view of continental collisions and invasions. Here we investigate Acacia s.l. from the Eocene to the Miocene to understand how it invaded the evolving landscapes of the Americas, Africa and Australia. This history highlights the convergent evolution within the paraphyletic genus as species invaded and dominated new arid landscapes that expanded at this time. Different lineages of Acacia s. l. evolved remarkably similar suites of adaptations in response to the increasing aridity, obscuring the independent evolutionary origins of ecological traits which we are only now discovering. 

The taxonomic history of Acacia s.l. has been and still is a complex topic. Taxonomists defined Acacia s.l. over centuries of plant discovery as botanists explored the world. This ad hoc compilation of species into a genus resulted in the amalgamation of species that have converged within a similar type of habitat but the main morphological characters that define Acacia s. l. are symplesiomorphies, not synapomorphies of a unique lineage. It is now accepted that the genus, in its broad sense, is not monophyletic and thus it has been split into three large genera and two small genera.