Abstract
The subtribe Celmisiinae (Asteraceae: Astereae) is a recently circumscribed monophyletic group distributed in Australasia. Species in Celmisiinae live in a diverse range of habitats; they can be dominant features of various vegetation types or rare obscurities; they can be conspicuous or discreet; and they can have widespread or narrow geographic ranges. The group contains ca. 159 species across six genera, including Pleurophyllum Hook.f., Macrolearia Saldivia, Damnamenia Given, Pachystegia Cheeseman, Celmisia Cass. and Olearia Moench pro parte. Traditional molecular phylogenetic studies, using one or a few genes have identified that Olearia and Celmisia are not monophyletic, and that the type species for Olearia (Olearia tomentosa DC.) is not part of Celmisiinae. Consequently, Olearia pro parte needs a generic revision, but many relationships at the generic and specific ranks remain unresolved. The importance of this group in the local Australasian floras and the remaining unresolved relationships make this an ideal group for clarifying taxonomic relationships. Ecological niche theory can provide important information regarding diversification, yet no detailed analysis of ecological niches has been undertaken before. Understanding the evolution of Celmisiinae could therefore be advanced through application of higher resolution phylogenetic analysis and the characterisation of ecological relationships among species and genera. The thesis uses phylogenetic, morphological, and ecological niche analyses to clarify taxonomic and ecological relationships in Celmisiinae. Phylogenomic and morphological analyses were undertaken with the aim of providing detail and support to resolve some of the undetermined relationships. The relationships between putative groups were tested using the recently developed target enrichment protocol Angiosperms353. Phylogenomic data were retrieved and phylogenetic relationships between the groups were estimated. The Angiosperms353 protocol was found to be useful at providing taxonomic information for Celmisiinae as the estimated phylogeny provided high support for some of the groups. Contrary to previous molecular analyses, the two main Celmisia clades were found to be sister taxa and monophyletic. In congruence with previous studies Olearia pro parte was identified as being polyphyletic with two main clades, Macrolearia and the rest. One of the putative clades, the Olearia furfuracea complex, was recovered in the phylogenomic analysis, and the members were previously found to lack character distinctions. A thorough morphological analysis was done to test whether there were sound morphological boundaries between five recognised species. Both quantitative and qualitative data supported the recognition of O. allomii and O. pachyphylla, and a revised concept of O. furfuracea to encompass O. thomsonii and O. townsonii. This investigation will be used as evidence to make a formal taxonomic treatment. A diverse group of ca. 30 Celmisia species was used to investigate aspects of ecological niche theory. Firstly, species distribution models (SDMs) were used to examine the relative effect of climate in determining geographic ranges. SDMs were fitted for each species and the extent to which each species filled their potential climatic niche was measured. The precision metric found a weak association for geographic ranges being set by climate, indicating moderate to low levels of environmental niche-filling occur in this group. This result has implications for the precision in both retrodicting paleo-ecological environments and predicting plant responses to future climate change. Secondly, a niche similarity analysis was carried out to analyse the relationship between i) ecological and phylogenetic and ii) ecological and morphological similarity between species. However, typically-used niche overlap indices do not explicitly consider disproportional overlap (i.e. size differences in overlapping situations), nor do they quantify the extent of non-overlapping niche space (i.e. separated, non-overlapping niches are always given a value of zero). An index (Relative Asymmetric Distance–RAD) was developed which overcomes these two constraints. The RAD index was demonstrated on a number of simulated and real species-pairs; it was compared against phylogenetic and morphological similarity in Celmisia; and it was used to investigate the association between regional species richness and species niche similarity. It was found that disproportional overlap can provide information regarding the discrimination between specialist and generalist species. The thesis makes a novel contribution to the taxonomy of Celmisiinae and the ecological understanding of its species. The investigations herein provide support for future taxonomic proposals; the investigations found the relationship between climatic niches and geographic ranges to be weaker than expected; and the investigations resulted in the newly designed RAD similarity index which behaves differently to other niche overlap indices.