Taxonomic delimitation and the evolutionary history of the Australasian Lautusoid group of Senecio (Asteraceae)
Thesis DisciplineEvolutionary Biology
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Taxonomic delimitation can be a challenging task for systematists, because of the dynamic and complex evolutionary processes that shape patterns of biodiversity. Yet, it is an essential aspect of biology, because it defines units of evolutionary significance, which form the basis for studying all aspects of biodiversity. In this thesis, I studied the taxonomic delimitation and evolutionary history of the Australasian Lautusoid group of Senecio at the infrageneric, species, and infraspecific level. Members of the Lautusoid group are morphologically very diverse and occupy a wide array of habitats. Moreover, the Lautusoid group has a large diversity of chromosome profiles compared to other Australasian Senecio, which indicates the possible occurrence of hybridization in its evolutionary history. These patterns of diversity make it an attractive system for various evolutionary and ecological studies. Despite these interesting characteristics and the inclusion of members of the Lautusoid group in a number of taxonomic treatments, it is not known how many and which species form the Lautusoid group. To determine the delimitation of the Lautusoid group and to investigate the origin of Lautusoid species with higher chromosome numbers, a molecular phylogenetic study was carried out. The results of this study indicate that the group is a morphologically and phylogenetically distinct Senecio lineage with an Australasian distribution. These results also highlight the important role of hybrid speciation in the evolutionary history of the Lautusoid group by identifying allopolyploid hybrids between members of the Lautusoid group and members of other Australasian lineages. An allopolyploid species complex that was found to be affiliated with the Lautusoid group, S. glaucophyllus, was the focus of subsequent studies. Senecio glaucophyllus and a morphologically similar informally named taxon, S. aff. glaucophyllus, were examined to determine if they are distinct species. The results confirm that the two taxa are indeed morphologically and genetically distinct. However, against expectation, this study revealed that S. aff. glaucophyllus is the true S. glaucophyllus and that the plants that were called S. glaucophyllus belong to a species that is presently unnamed. This taxon, tentatively called S. “pseudoglaucophyllus”, aligns with S. glaucophyllus sensu Ornduff excluding S. glaucophyllus Cheeseman. In order to revisit the current classification of recognizing four infraspecific groups for S. “pseudoglaucophyllus” and to propose taxonomic recommendations, studies that look into its morphological and genetic diversity were performed. The results of these studies show that patterns of morphological variation in S. “pseudoglaucophyllus” are not congruent with patterns of genetic variation and that neither supports the current classification in which four infraspecific groups are recognized. Because infraspecific taxon boundaries cannot be unambiguously determined for S. “pseudoglaucophyllus”, this species is therefore best regarded as a single variable New Zealand species for which infraspecific groups should not be formally recognized.