Molecular phylogeny of Acacia Mill. (Mimosoideae: Leguminosae): Evidence for major clades and informal classification

Sequences of nuclear ribosomal DNA internal (ITS) and external (ETS) transcribed spacers were used to generate a phylogeny of Acacia Mill. s.str. (synonyms: Acacia subg. Phyllodineae (DC.) Seringe; Racoserma Mart.). This study included 109 exemplar taxa from all seven sections recognised in previous classifications, and represents the largest sampling of diversity for molecular phylogenetics of Acacia s.str. undertaken so far. Four main clades were identified from the combined dataset of ITS and ETS using parsimony and Bayesian analyses. Two of these clades consist mostly ofuninerved phyllodinous taxa assigned to sect. Phyllodineae. One clade includes taxa related to A. victoriae and A. pyrifolia, and the second comprises taxa in the A. murrayana species group. These taxa occur predominantly in semi-arid and arid regions. Relationships also resolve the previously identified Pulchelloidea clade, which includes members of sects. Pulchellae, Alatae, Phyllodineae and Lycopodiifoliae. A large clade with limited phylogenetic resolution was also identified (the "p.u.b. clade"). This is an assemblage of plurinerved and uninerved phyllodinous taxa and also bi-pinnate taxa from sect. Botrycephalae. Clades are discussed with reference to morphological characters, and while some morphological states are correlated with clades, including seedling ontogeny, inflorescence and phyllode nerves, clear synapomorphies remain to be identified. Traditional classifications of Acacia s.str. are artificial and a preliminary informal classification based on phylogenetic relationships within Acacia s.str. is proposed.