Reconstructing reticulate relationships in the polyploid complex of Leucanthemum Mill. (Compositae, Anthemideae)

The genus Leucanthemum consists of ca. 56 taxa occurring mainly in Southern and Central Europe. While there are 19 diploid taxa (2n = 2x = 18) the rest of the genus is formed by an unbroken polyploid chain ranging from tetraploid (2n = 4x = 36) to dokosaploid (2n = 22x = 198). Because of richness in polyploids this genus provides an ideal study system to examine various aspects of polyploidy. This thesis is the starting point to unravel phylogenetic relationships within the whole genus. In this study sampling of all recognized taxa in the genus Leucanthemum is provided with the main aim to reconstruct phylogenetic relationships. The thesis is divided into three chapters with focus on: 1) phylogeny of diploids and homoploid hybrid speciation incidence, 2) phylogeny of all taxa including polyploids, 3) phylogeny and evolutionary processes within L. glaucophyllum group and closely related species. Phylogenies are reconstructed with usage of low-copy nuclear genes sequenced by 454 sequencing accompanied by chloroplast markers. Species tree is constructed in the first Chapter together with species network and hybrid index for all diploid taxa. It reveals that Leucanthemum is monophyletic and that fifteen out of nineteen diploid taxa experienced homoploid hybrid speciation or severe gene flow among species. As a consequence the particular branches in the phylogeny gain rather low support but with robust division of diploids into two groups present in all analyses. In the second Chapter the phylogeny of all taxa is reconstructed as species network which recovers high level of reticulation among them with main finding that taxa from the same geographic area show affinity irrespective of their ploidy level. The third Chapter focuses in more detail on a smaller group of high polyploids related to a decaploid L. glaucophyllum. With reconstruction of species network, nested clade analysis on chloroplast network, and AFLP clustering it brings insights into relationships in this group. It also sheds light on the phylogeography of L. pallens and suggest that gene flow among the same and different ploidy levels is likely occurring. Furthermore new octoploid race is found in Esterell Massif and its relation to other taxa is discussed. The results pinpoint hybridization as one of the major processes in the evolution of the genus Leucanthemum. It influences speciation on the diploid level, enables formation of polyploids and contributes to the reticulate evolution among them in general, and specifically in taxa related to L. glaucophyllum