Introduction

Mimosoideae are a dominant plant clade in Australia with more than 1000 taxa recognised. Most species belong to genus Acacia s.s. Mill. and evolved in Australia during the post-Gondwanan isolation. Very few species (<20) belong to genera that evolved outside Australia (Vachellia Wight & Arn., Senegalia Raf.; until quite recently both included under Acacia s.l.) and have subsequently invaded into Australia (Chapter 2). Most of these are descended from individuals that immigrated into Australia and New Guinea prior to European migrations (hereafter pre-colonial species), while a few were either accidentally or deliberately introduced by Europeans (hereafter colonial species). The relative abundance and distribution of the species varies significantly between early and later invaders: the later colonial invaders show wider or rapidly expanding distributions and superior dominance status in the communities where they are found (Table 3.1; Australian Biological Resources Study 2001; Kriticos et al. 2003). The early colonial species range from being (more usually) abundant to locally dominant, in some instances (Table 3.1). This suggests that either trait differences between the species have affected their relative performance under modern, post-colonial systems of native vegetation management, or that human activities have particularly favoured the spread of post-colonial species.