What continent are the genuses Allocasuarina and Acacia mainly native to? 
Allocasuarina:  They are endemic to Australia, occurring primarily in the south. Acacia:  Initially it comprised a group of plant species native to Africa and Australia, with the first species "A. nilotica" described by Linnaeus. Acacia:  It turned out that one lineage comprising over 900 species mainly native to Australia was not closely related to the mainly African lineage that contained "A. nilotica"—the first and type species.
mainly native to Australia