Abstract/Summary

Saxifraga L. (Saxifragaceae) is a species-rich genus (> 440 spp.), which occurs mainly in mountainous and arctic regions of the Northern Hemisphere. The species-richness of Saxifraga, and its strong ecological and morphological differentiation make it an ideal model system for studying alpine lineage evolution. However, those efforts require a robust phylogenetic framework. This thesis explores the evolutionary relationships within Saxifraga by designing hybrid-capture targets that are compatible with existing high-throughput sequencing data, to produce the most densely sampled phylogeny for the genus based on sequence information of 329 nuclear loci. High sequence coverage is obtained for target loci, although not all loci are retrieved for all sections of the genus, and certain taxa have a high incidence of paralogous copies due to the wide occurrence of polyploids in Saxifraga. DNA samples are predominantly sourced from museum material and the effect of locus retrieval and paralog detection is tested against sample age, where a slow decline in retrieved target length is observed and, importantly, a decline in paralog detection occurs with sample age that could mask high persistence of paralogous copies in phylogenomic datasets. The species tree based on newly generated and publicly available data confirms many recent taxonomic revisions and finds overall higher support for the topological placement of monophyletic sections. However, slight revisions are suggested for sect. Ciliatae and placement of Saxifraga cuneifolia L. in sect. Gymnopera is tenuous due to a complex evolutionary history likely involving intersectional introgression. A new set of divergence time estimations is performed with additional outgroups and calibration points. Relatively recent nodes were found to be older than had been previously estimated based on phylogenies of few concatenated loci. Likely, all sections of Saxifraga existed within the Miocene during strong climate cooling and mountain uplift in its geographic range. Finally, the adaptation of Saxifraga to high solar radiation conditions, that are typical for the alpine biome, is explored within a phylogenetic framework. Leaf temperature data and associated environmental data is presented from a common garden experiment. The leaf temperature increase over air temperature from heating through solar irradiance differs among taxa, while leaf functional traits that are known to impact temperature regulation ability had no effect on the ratio of leaf heating. However, closely related taxa are shown to have a similar leaf heating response to radiation and some clades are more abundant in taxa that are more likely to overheat with high radiation than others. Unlike the clades that can efficiently manage leaf temperatures towards an optimum, these clades are prone to reach unfavourable conditions upon exposure and are suggested to be more prone to future climate change.