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ItemPhylogeny and biogeography of three groups of Acacia (the A. victoriae, A. pyrifolia and A. murrayana groups) in arid Australia(University of Melbourne, 2006)Acacia subgenus Phyllodineae is a monophyletic group, characterised by phyllodinous leaves. It is the largest subgenus in the genus Acacia sensu lato, comprising more than 900 species, largely confined to Australia. On the basis of recent findings, a major revision of Acacia has been proposed to raise the subgenera to generic rank, with the name Acacia to be applied to subg. Phyllodineae. The relationships of infrageneric groups within subg. Phyllodineae, however, are not fully resolved. There is thus a need for phylogenetic studies among the Australian acacias. The study presented here focuses on a group of arid species, addressing variation within a wide-spread species (A. victoriae) and the phylogeny of related taxa currently considered informally to represent three groups of 19 species. PCR-RFLP and DNA sequencing were applied to determine the genetic variation of A. victoriae, in addition to morphological data. Three groups (subspecies) were found: (1) populations with small, oblong and hairy phyllodes, distributed mainly in Central Australia (subsp. arida); (2) populations with narrow linear to broad phyllodes and more widely distributed, and (3) populations with long linear phyllodes, distributed in the northern part of Australia. The phylogenetic relationships of species within the A. victoriae, A. pyrifolia and A. murrayana groups were analysed using DNA sequences of the internal and external transcribed spacer regions of nuclear ribosomal DNA and the trnL-F region of chloroplast DNA. The findings indicated that the A. murrayana group is monophyletic, whilst the A. pyrifolia taxa are nested within the A. victoriae clade. Based on a phylogenetic analysis of taxa sampled across subg. Phyllodineae, the A. murrayana group was found not to be closely related to the A. victoriae clade. This study demonstrated the advantages of the ITS and ETS nrDNA regions in resolving relationships at the specific level and between populations in a variable species. The parsimony analysis based on the ITS region provided more resolution at specific level than the ETS region. The trnL-F cpDNA region provided fewer informative characters and less resolution than the nuclear region. The distributions of taxa within the A. murrayana and A. victoriae clades are mainly in the arid (Eremean) region of Australia, and endemic related taxa show allopatric patterns, which have the potential to contribute to an understanding of the evolutionary history of the Eremean zone. A cladistic biogeographic approach was conducted based on the phylogenetic analysis of these three species group using the ITS and ETS DNA sequences. Results of paralogy-free subtree analysis indicate that the earliest regions to differentiate were Arnhem and the North-West semi-arid region (including Dampierland, Ord- Victoria Plains and Tanami), relative to the other regions occupied by these acacias. In arid central Australia, the Central and MacDonnell Ranges are most closely related to the South-West Interzone (Coolgardie bioregion). The Eastern Desert, Western Desert and Pilbara are related as a group, which does not support the idea that these two deserts have been colonised by these acacias independently from different centres on the margin of the continent. The widespread and genetically variable A. victoriae species complex also showed regional differentiation, one pattern being the relationship of the Northern subtropical regions, from the southern Kimberley east to the Gulf Uplands and Cape York. It is argued for these acacias that the underlying differentiation of areas of endemism in the Eremean zone of Australia is relatively old, with increasing aridity during the Cenozoic, not withstanding that present-day species pairs and intra-specific variation might relate to more recent shifts in vegetation and arid cycles.