School of BioSciences - Theses

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    Systematics and biogeography of Spyridium with a focus on Spyridium parvifolium and its hybrids
    Clowes, Catherine ( 2022)
    Spyridium is a genus of c. 45 species endemic to south-western and south-eastern Australia, with a disjunct distribution across the Nullarbor Plain and Bass Strait. The genus also includes several morphologically distinct phrase name taxa. Spyridium parvifolium is a widespread and morphologically variable shrub from south-eastern Australia. Several varieties and forms of this species have been recognised, but there is disagreement on the accepted taxonomy between Australian states. Spyridium parvifolium is known to hybridise with S. daltonii in the Grampians and is thought to hybridise with S. vexilliferum in locations where these taxa co-occur in western Victoria and south-eastern South Australia. The aim of this research project was to develop a comprehensive molecular systematic understanding of Spyridium, and S. parvifolium and its hybrids, to inform the treatment of Rhamnaceae in the Flora of Australia (Kellermann et al. 2022-). The objectives were to investigate: the species circumscription and biogeographic history of Spyridium, the infraspecific taxa and phylogeographic patterns of S. parvifolium and introgression associated with this species (i.e. S. xramosissimum and S. parvifolium x S. vexilliferum). Entire chloroplast genomes (c. 160k base pairs) and the nuclear ribosomal array (18S–5.8S–26S; c. 6k base pairs) were analysed using both Bayesian and Maximum Likelihood phylogenetic methods. In total sequences from 230 samples were analysed across these phylogenies, including representatives of all recognised species of Spyridium, six phrase name taxa, seventy-two accessions of S. parvifolium, eight putative hybrids and four outgroup taxa. This study provides the most comprehensive phylogenies of Spyridium and S. parvifolium to date. For Spyridium, several biogeographic patterns were identified, including deep diverging clades of taxa endemic to Western Australia, New South Wales and Tasmania. Several taxa were identified as polyphyletic (e.g. S. eriocephalum and S. phylicoides), warranting taxonomical review. For S. parvifolium, early divergence of individuals from west of the Murray Darling Depression, isolation on the inland side of the Great Dividing Range and recent seed-mediated gene-flow across Bass Strait were identified in the chloroplast genome phylogeny. The variants of S. parvifolium were not supported as genetically distinct suggesting the infraspecific recognition of var. parvifolium and var. molle in Tasmania is not warranted. Molecular evidence of introgression between S. parvifolium and both S. daltonii and S. vexilliferum was identified, providing molecular support for hybrids also inferred from intermediate morphology. Other findings include inferred parentage, unidirectional introgression and recombination of the nuclear ribosomal array for some hybrid accessions.
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    Phylogenomics, molecular evolution and extinction in the adaptive radiation of murine rodents
    Roycroft, Emily Jane ( 2020)
    Adaptive radiation plays a significant role in the generation of biological diversity, and the advent of modern sequencing approaches has unlocked a new genomic perspective on this process. Genomic-scale data from the across the diversity of adaptive radiations can provide unprecedented resolution of the phylogenetic, biogeographic and molecular context of diversification. Murine rodents (Murinae: Rodentia) are a recent and rapid adaptive radiation that make up > 10% of mammal species. Murines have repeatedly colonised new geographic areas and island systems in the Eastern Hemisphere, frequently as a result of overwater transitions. Recurring adaptive radiation, ecological character displacement, and convergent evolution across Murinae make them an ideal model for studying adaptive radiation, especially in the Indo-Australian region. Within broader Murinae, the Hydromyini are a speciose Australo-Papuan radiation that diversified following an overwater colonisation from Sunda to Sahul ca. 8 Ma. Previous multilocus studies did not provide sufficient phylogenetic resolution of the rapid diversification of Hydromyini, and did not adequately sample taxa to reconstruct their complex biogeographic history. In addition to unresolved biogeography, the endemic Australian clade within Hydromyini has suffered the highest rate of recent mammalian extinction in the world. The rapid decline of Australian rodents is thought to be primarily the result of predation by feral cats, combined with other factors such as anthropogenic land clearing. There is little information about the pace of decline in eight species that went extinct on the Australian mainland in the last 150 years, and it is unclear whether these species had suffered longer term declines that predate the arrival of Europeans into Australia in 1788. To resolve these outstanding issues, I develop a novel exon capture approach for murine rodents. Firstly, I investigate the degree of congruent and conflicting phylogenomic signal in a rapid radiation, using genus-level relationships in the Hydromyini as a model example. My results show that in a number of cases, strong conflict is not reflected in branch support metrics obtained using either maximum likelihood or summary coalescent approaches. This result is significant, as it suggests that approaches commonly used to estimate support in phylogenomic data can fail to detect uncertainty in the face of underlying genealogical heterogeneity. Further leveraging this novel exon capture design, I generate a robust phylogenomic tree based on > 350 samples across the Australo-Papuan continent, including extant and recently extinct species in Hydromyini. With these data, I reconstruct the species-level evolutionary and biogeographic history of the Hydromyini across Sahul, recovering numerous examples of overwater colonisation between regions. Consistent with the geomorphological hypothesis that the New Guinea lowlands emerged after the orogeny of the Central Cordillera, I find evidence for increasing ecological opportunity in the Hydromyini from approximately 5 Ma. This first species-level phylogenomic study spanning the entire Sahul region provides a baseline example for future comparative studies that seek to reconstruct the biogeographic drivers of diversification in Sahul at a continental scale. Using exon capture and whole-exome sequencing data from extinct and extant species, I place recently extinct Australian rodents in a phylogenomic context for the first time. I recover no marked evidence of genetic erosion in five extinct species at the time of specimen collection, in comparison to extant species with present-day low allelic diversity. This indicates that the decline of recently extinct Australian rodents occurred extremely rapidly, and its onset likely did not predate European settlement. Additionally, my results taxonomically resurrect a species from extinction, Gould’s mouse (Pseudomys gouldii), which survived as a single island population in Shark Bay, Western Australia (currently classified as P. fieldi). Finally, I generate whole exome data from 38 species in the global radiation of Murinae to examine patterns of positive selection and convergent evolution. I uncovered pervasive positive selection across genes associated with diet, digestion and taste across Murinae, and increased rates of adaptive evolution in carnivores compared to omnivores. Limited evidence for molecular convergence in worm-eating specialists Paucidentomys and Rhynchomys suggests a role for developmental phenotypic control in this striking example of ecological convergence. Broadly, my results indicate that the pronounced ecological and phenotypic shifts that are hallmarks of adaptive radiations may also drive corresponding shifts in the pace and pattern of molecular evolution across the genome. Together, the work in this thesis is fundamental to the understanding of diversification, adaptation and extinction in the Australo-Papuan region, and provides an extensive genomic resource for future studies.
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    The bryophyte flora of Lord Howe Island: taxonomy, diversity and biogeography
    Meagher, David Anthony ( 2018)
    Before this study the known Lord Howe Island bryophyte flora (mosses, liverworts and hornworts) totalled 173 species, consisting of 131 mosses, 40 liverworts and 2 hornworts. For this study I conducted one month of field studies on the island, during which I collected more than 650 specimens, and also studied collections from the island held in Australian herbaria and other collections available in overseas herbaria. Fourteen moss, 32 liverwort and 1 hornwort species are newly reported from Lord Howe Island, including one liverwort new to science. A further 2 moss and 2 liverwort varieties are also new to the island. Twenty-eight moss and 11 liverwort species are discounted from the island’s flora, as well as 3 moss varieties and 1 liverwort variety. As a result, the known bryophyte flora now totals 178 species, consisting of 117 moss species (122 taxa), 58 liverwort species (60 taxa) and 3 hornwort species. These totals exclude 5 moss and 2 liverwort species whose taxonomic status or presence on the island is considered uncertain. One liverwort variety, Heteroscyphus echinellus var. echinellus, is new to Australia. Fourteen bryophyte species and one variety are endemic to the island. Spiridens muelleri, previously thought to be the same as S. vieillardii from New Caledonia, is shown to be a separate species endemic to Lord Howe Island. Chiloscyphus howeanus is also shown to be a legitimate species endemic to the island. Cololejeunea elizabethae is described as a new species, also endemic to the island. Trachyloma wattsii, considered to be endemic to Lord Howe Island, is supported by a molecular analysis as a legitimate species most closely allied to T. planifolium. Confusion about the correct identities of the two Ptychomitrium species on the island is resolved through a revision of the genus for Australia. A previously unrecorded morphological character of Atrichum androgynum is described from a study of Lord Howe Island plants, and a molecular analysis shows that South American plants previously ascribed to A. androgynum do not belong to that species. Hypnodendron vitiense is shown to be paraphyletic, but not as circumscribed by Touw (1971). The Lord Howe Island plants appear to belong to a morphologically cryptic species distinct from H. vitiense s.str, and substantial genetic variation within H. vitiense subsp. australe as currently circumscribed suggests that it might include more than one taxon. Other molecular investigations clarify the relationship between Lord Howe Island populations and mainland Australian populations of a number of moss species. An original and novel investigation of the potential modes of transport of bryophyte propagules to and from the island is made, and a hypothesis is formed about the origins of its bryophyte flora and the biogeographic relationships to the Australian land mass and other western Pacific islands, including New Zealand and New Caledonia. The nearest region of the Australian mainland is shown to be the most likely origin of most of the island’s bryoflora, with the injection of propagules into the high-level jet stream by storms the most likely dispersal mechanism. The presence of numerous otherwise tropical species on the island is probably a result of dispersal by tropical cyclones moving into the Pacific from north-eastern Australia. Migratory birds are shown to be another potential vector for bryophyte dispersal to the island.
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    Macro-evolution in brittle stars
    Bribiesca Contreras, Guadalupe ( 2018)
    Conspicuous large-scale diversity patterns and the disparity of species-richness across different taxonomic groups have fascinated naturalists for centuries. In recent years, advances in molecular techniques have facilitated the generation of large amounts of genetic data and have permitted the investigation of long-standing macro-evolutionary questions in a phylogenetic framework, even when the fossil record is scant. With the deep-sea being largely unexplored, many questions remain unanswered and processes affecting diversity in the oceans are far less understood than in terrestrial or aquatic ecosystems. Brittle stars have become a great model to study evolutionary processes, as an extensive genomic dataset has been generated. In this thesis, I aimed to identify large-scale diversity patterns in the oceans and to investigate their underlying processes in a phylogenetic framework. I used this extensive dataset, global distributional records, and novel phylogenetic approaches to investigate major processes at global scales. I investigated the dynamics of bathome shifts and the role of the deep-sea in generating diversity. The findings of bathymetric ranges being highly conserved, and shifts being infrequent, served as a baseline for the other chapters where evolutionary processes were investigated within bathomes. I also investigated the effect of the emergence of biogeographic barriers in shaping diversity patterns of tropical, shallow-water brittle stars. The temporally and spatially concordant divergences of clades, concordant across families, evidenced the role of plate tectonics in shaping spatio temporal patterns of diversity. Similarly, the role of geological processes in the evolution of the fauna of southern Australia was investigated. Three major components have been identified for this fauna, which are the result of geological and historical processes. Recent colonisations, either from tropical species colonising higher latitudes or temperate taxa dispersed from other regions in the Southern Ocean, have been identified based on fossil evidence. However, although a Gondwanan component has been suggested, fossils from the late Cretaceous are scarce, limiting our knowledge about the effect of the break-up of Gondwana. Revisiting this question using one of the most complete metazoan phylogenies to date reaffirm the important role of the Antarctic Circumpolar Current (ACC) in shaping diversity patterns in the Southern Hemisphere, but also of the break-up of Gondwana. Lastly, I investigated colonisations of anchihaline environments. Although several marine taxa have cave-adapted lineages, only three brittle stars have been reported to occur in these environments. As, these species belong to different families, they must represent independent colonisation events. I used evidence from multiple loci to perform species delimitation using robust methods, and assessed models of origin of cave fauna in a phylogenetic framework, considering life-history traits, and demographic history for the cave population. The questions addressed in this thesis evidence the power of phylogenomic approaches that in combination with extensive distributional datasets, shed light into macro-evolutionary processes. The results presented herein contribute and advance our knowledge about diversity and evolutionary processes in our oceans, and provide a framework for future research.
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    Evolution and ecology of the Australian Heliozelidae (Adeloidea, Lepidoptera)
    Milla, Elizabeth ( 2018)
    The Heliozelidae (Adeloidea: Lepidoptera) are a family of small, primitive day-flying moths with a worldwide distribution. In recent years, potentially hundreds of new species have been collected around Australia, predominantly in the southwest region of Western Australia. Overall, our observations suggested that many Australian species have evolved independently from other groups in the family. In particular, there is one group of Australian species possessing a unique pollen-carrying abdominal cleft that have established a remarkably close association with species of the Rutaceae (Sapindales) plant genus Boronia. In order to understand the evolution of the Australian Heliozelidae, a robust phylogenetic framework of the Heliozelidae family was required. Additionally, examination of the origins and purpose of the unique morphology of pollen-carrying species and the nature of the associations with their Boronia hosts was crucial to understand their ecological role. Thus, in the first part of this thesis (Chapters Two and Three), I focused on resolving the phylogeny of the worldwide Heliozelidae family and placing the Australian species within it. In Chapter Two, I generated a preliminary phylogeny identifying the major Heliozelidae clades and identify Australia as one of the regions with high undescribed diversity. In Chapter Three, I estimated a fully resolved time-calibrated phylogeny of the major heliozelid clades, with an ancestral range estimation tracing the origins of the family to the Australian region around 96 Mya, during the Late Miocene. In the second part of the thesis (Chapters Four and Five), I focused on the group of Western Australian species that has formed a remarkable association with species in the plant genus Boronia. In Chapter Four, I presented a molecular phylogeny of the Boronia pollinator moths and found preliminary evidence of cospeciation between the moths and their Boronia hosts. In Chapter Five, I described the remarkable active pollination behaviour in three different species of Boronia pollinator, and established the obligate pollination relationship between B. megastigma and its heliozelid pollinator. The findings from this thesis suggest that Heliozelidae play an important role in the Australian environment, exemplified through their close pollination association with the predominantly Australia genus Boronia. Thus, further research into this family of small day-flying moths, which has been poorly studied in Australia until now, is required to better understand their significance.
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    Assessing patterns and processes of deep-sea diversity to inform conservation management
    Woolley, Skipton Nicholas Charles ( 2017)
    Deep-sea ecosystems –- from the continental shelf to the deep abyssal plain –- are unique, biodiverse and burdened by a variety of pressures. Models that describe patterns of biodiversity and the processes that shape these distributions are a fundamental tool of conservation management. Until we better understand the distribution and drivers of biodiversity, we are limited in our capacity to develop strategies to conserve diversity. Unlike terrestrial or more accessible coastal marine environments in which relatively data-rich modelling provide reliable models of biodiversity patterns, deep-sea environments are extremely difficult and expensive to survey. As a consequence, many existing models and maps that describe deep-sea biodiversity are coarse-scale, regionally constrained, inaccurate and patently inadequate for supporting important conservation decisions. Using new unique datasets and new analytical methods I characterise patterns of deep-sea seafloor biodiversity to help inform conservation management for the deep-sea at oceanic scales. In this thesis, I produced comprehensive models and maps of deep-ocean biodiversity by combining novel modelling approaches that dealt with sparsely sampled data with recently compiled, high-precision, but geographically sparse global data of deep ocean invertebrate biodiversity. My novel modelling framework uses statistical modelling approaches to characterise statistical relationships between species distribution patterns, physical and biogeochemical data, and species detectability. My models provided some of the first broad scale spatially explicit models of deep-sea benthic species richness, turnover and irreplaceability. Using these models, I test hypotheses on the processes that shape deep-sea species biodiversity. The results presented in this thesis will help inform the United Nations' new implementing agreement on Biodiversity Beyond National Jurisdictions (BBNJ), designed to regulate human activities on the high seas and conserve marine life.
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    Comparative phylogeography and diversity of Australian Monsoonal Tropics lizards
    Laver, Rebecca Jan ( 2016)
    Tropical savannah biomes cover ~20% of the world’s landmass, however the biodiversity encompassed within these environments and the underlying processes that have shaped it remain poorly understood. Recent increased research to address this knowledge gap have begun to reveal surprisingly high amounts of deep, geographically-structured diversity, much of which is cryptic or hidden within morphologically similar species complexes. These patterns are especially emphasized in vertebrate taxa which are intrinsically linked to rock escarpments and ranges that dissect the savannah woodlands and grasslands of many of these biomes, hinting at a role of heterogeneous topography in structuring diversity. The remote Australian Monsoonal Tropics (AMT) spanning the north of the Australian continent is a particularly vast, and relatively undisturbed, tropical savannah region. Recent increased surveys are revealing numerous new species and endemism hotspots, indicating we are only just beginning to uncover the true biodiversity levels within this biome. Not only is there a relative paucity of knowledge regarding the present diversity within this region, but there is also limited understanding of how this diversity came to be. Phylogeographic studies can assist us in establishing current patterns of diversity and their evolutionary significance within regions and biomes. Furthermore, by comparing and contrasting the patterns and timing of diversification within and between biomes for multiple ecologically diverse taxa, we can begin to elucidate the history of these biomes and the environmental processes that have shaped the diversity we observe today. In this dissertation I aimed to better assess and establish true patterns of biodiversity and endemism within the Kimberley region of the AMT (Western Australia), and to place these patterns within a broader continental context using intra- and inter-biome comparisons in related taxa. Using geckos as a model system I took a comparative phylogeographic approach, integrating advanced next-generation genetics and morphology to establish patterns and timing of diversification across ecologically variable taxa. Within all Kimberley taxa I studied, I uncovered high levels of cryptic diversity. Much of this diversity involves especially short-range endemic lineages concentrated in key regions typically with one or more of the following factors: highly mesic conditions, island or insular environments, and unique or complex geological formations. In recognising these areas I have provided evidence of novel biodiversity hotspots and emphasised the significance of others as representing important “refugia” within the Kimberley that allow persistence and facilitate divergence of lineages through harsh periods of environmental change. These findings indicate diversification patterns are shaped by complex interactions of climatic variation, topography, and species’ ecology, allowing inference of biogeographic history and a greater ability to predict impacts of future environmental change.
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    Evolution and biogeography of Australian tropical freshwater fishes
    Shelley, James ( 2016)
    Australia’s freshwater fish fauna is the most depauperate of any continent (256 formally recognised species), although endemism is exceptionally high (74%), largely due to its arid climate and history of isolation from other land masses. The Australian Monsoonal Tropics (AMT) biome in the tropical north is an exception. The AMT encompasses 33% of the Australia landmass, but contains 65% of the Australian fish fauna and, in a global context, the biome and many of its catchments contain moderate to high species richness relative to their size. However, the biodiversity, evolution, and biogeography of the AMT’s fish fauna remain poorly studied relative to the rest of the continent. In this thesis I utilise samples from the most comprehensive region-wide collection of freshwater fish molecular and distributional data in the AMT to help answer three fundamental questions regarding the regions freshwater fish fauna: (1) what is the true biodiversity of the AMT; (2) what are the key evolutionary processes driving and maintaining freshwater fish diversity across the region, in particular the highly endemic fauna of the Kimberley bioregion; and (3) what are the key patterns in diversity and distributions across the landscape and how can they be arranged into a cohesive biogeographic framework? First, I conducted a multigene molecular assessment of species boundaries in the AMTs most speciose freshwater family (Terapontidae) in order to assess the phylogenetic relatedness of terapontids in northwestern Australia (including the Kimberley) to the level of population, and to identify any unique genetic lineages that likely represent undescribed ‘candidate species’. I demonstrated the presence of 13 new candidate species within the Kimberley, more than doubling previous estimates of terapontid diversity in the region. Second, I conducted an assessment of morphological (morphometric and meristic) data from seven of the genetically defined candidate taxa, and the four previously described species within the genus Syncomistes to see if the seven candidates can be discriminated morphologically and to determine which characters best delimit taxa. I found an impressive array of meristic and morphometric character differences between species within Syncomistes and determined that the head, particularly feeding structures such as the jaw and dentition, were the most important morphological features in discriminating between taxa. Third, I looked for congruence between phylogenetic patterns in Kimberley terapontids and both past (low sea-level)/present (high sea-level) geological barriers and pathways as identified by GIS analysis, and tested the general hypothesis that geographic isolation of terapontid lineages during Pliocene and Pleistocene high sea-levels triggered the onset of reproductive isolation between taxa thus driving rapid speciation in the region. I found that most Kimberley terapontid species arose during the Plio-Pleistocene glacial cycles and are at different stages of allopatric divergence and speciation caused by the same vicariant processes. The results support the hypothesis that changing sea levels during late Pliocene and Pleistocene glacial cycles are a key driver of speciation and distributional patterns in the Kimberley. Fourth, I combined phylogenetic, biogeographical and diversification analyses to examine the nature of the Kimberley as a mesic refugium. Specifically, I investigate the tempo and timing of endemic diversification to see if the Kimberley has been a ‘museum’ or a ‘cradle’ of diversification. My combined molecular clock estimates and likelihood-based historical biogeographic reconstructions suggest that terapontids recently transitioned into the Kimberley from the east during the late-Miocene. Outstandingly, ~80% of Kimberley terapontids diversified within the region in the last 3 Ma. Further diversification analyses identified a single significant shift in diversification rates ~1.4 Ma that corresponds with a significant change in global climate midway through the Pleistocene. Given these finding my findings suggest that the Kimberley has been acting as a cradle of Neoendemism. Fifth, I generate a bioregionalisation of the freshwater fish in the AMT using the Simpson’s beta dissimilarity metric, and then assess the relationships of the biogeographic regions to their current environment using generalised dissimilarity modeling (GDM). I also estimate true species richness across catchments using the Chao 2 index in order to identify major sampling gaps. I propose three major freshwater fish bioregions and 14 subregions that differ substantially from the current bioregionalisation scheme. I found that species turnover was most strongly influenced by environmental variables that reflect changes in terrain (catchment relief and confinement) and productivity (NPP and forest cover). Current river orientation and historic connectivity between rivers during low sea-level events also appear to be influential. Three focal points of species richness and two of endemism were identified in the AMT, considerably expanding upon the spatial understanding of these patterns. Finally, a number of key sampling gaps are identified that need to be filled in order to fully refine the proposed regionalisation. Overall the results of this thesis add considerably to biodiversity estimates and the taxonomic knowledge of freshwater fish communities in the AMT. It also helps determine the major drivers of speciation in the Kimberley, the mode of diversification, and provides insight into the regions function as an evolutionarily important mesic refugium. Finally, it provides a modern freshwater bioregionalisation of the AMT and helps to determine the environmental variables driving community change across the landscape. These findings have important ramifications for the conservation of Australia’s tropical freshwater fishes. The Kimberley in particular is highlighted as not only an important evolutionary refugium, but also as a catalyst for narrow range endemic speciation. As a result the regions contains some of the most threatened freshwater fish communities in Australia.
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    Phylogeny and phylogeography of Zieria (Rutaceae)
    Barrett, Rosemary Ann ( 2016)
    Zieria (Anthophyta: Rutaceae) is a predominately Australian genus of shrubs and small trees, consisting of 59 Australian species and one species endemic to New Caledonia. Although there has been considerable taxonomic revision of this genus in recent decades, largely based on morphology, a comprehensive molecular phylogenetic study that would include as many currently-recognised taxa as possible was clearly needed. Using five chloroplast markers (rpl32–trnL, trnL–F, trnQ–5'rps16, trnS–G and 3'trnV– ndhC) and two nuclear DNA markers (ITS and ETS) this study undertook phylogenetic analyses in order to understand relationships, evolutionary processes and taxonomic issues in Zieria, and to interpret biogeographic patterns. Both Bayesian inference and maximum parsimony methods were employed. Almost all species of Zieria were represented in separate analyses of the cpDNA and nrDNA datasets, with the monotypic sister genus Neobyrnesia used as the outgroup. The results show that relationships within Zieria are complex; widespread incongruence was revealed between cpDNA, nrDNA and currently recognised taxa. A combination of factors is suggested to explain this, including regional cpDNA introgression (chloroplast capture) and incomplete lineage sorting, and the need for taxonomic revision of some taxa. The nrDNA provided greater support for monophyly of species than cpDNA, and potentially a better indication of phylogeny. However, deeply divergent paralogues of nrDNA were detected in some taxa, making the assessment of phylogenetic relationships more challenging, and highlighting some possible pitfalls in using nrDNA for phylogenetic reconstructions. The phylogenetic relationship of Australian taxa and Z. chevalieri, the single endemic New Caledonian species, is of particular interest in terms of the long-standing debate over the history of New Caledonia and its flora. The placement of Z. chevalieri differed between cpDNA and nrDNA trees. The cpDNA phylogeny placed Z. chevalieri as sister to all other species in the genus, suggesting that the earliest divergence was between lineages of New Caledonia and Australia, and that differentiation of species occurred through vicariance. In contrast, Z. chevalieri was placed higher in the nrDNA tree, which could suggest later dispersal, over water or via past exposed land in the Tasman Sea rather than older vicariance between Australia and New Caledonia. However, the results did not favour one hypothesis over another, and the debate will continue. A phylogeographic study of one widespread species, Zieria arborescens, was also undertaken, focusing on populations in the wet forests of Victoria and Tasmania. The cpDNA was not highly informative but provided some evidence of Tasmanian–eastern Victorian connections, interpreted as past geographic connectivity during periods of low sea-level now severed by Bass Strait. Finally, a number of taxonomic issues arising from the results of this project are discussed, and recommendations are made for reappraising and possibly re-circumscribing several taxa. In some cases this might require the description of new species based on variation between populations (e.g. Z. smithii and Z. furfuracea), or recircumscription of taxa to effect monophyly (e.g. Z. arborescens). Some taxa might be considered conspecific based on noteworthy similarities of morphological and genetic characters (as seen in this study) and the geographic proximity of populations (e.g. Z. buxijugum and Z. parrisiae; Z. alata and Z. madida; Z. verrucosa and Z. vagans; Z. caducibracteata and Z. arborescens; and Z. minutiflora and Z. obovata).