Importance of polyploidization for diversification of hyperdiverse Euphorbia subgen. Esula : polyploidy is positively correlated with increasing latitude, but negatively with

Abstract Background and Aims Polyploidy is one of the most important evolutionary pathways in flowering plants, significantly contributing to their diversification and radiation. However, little is known about how this process has contributed to the high diversity of Euphorbia (Euphorbiaceae), one of the largest genera of flowering plants. Our aim was to determine the incidence of polyploidy and the evolutionary dynamics of genome size differentiation across the different lineages (sections) of Euphorbia subgen. Esula. Additionally, we investigated whether the latitudinal and elevational distribution of polyploids within the subgenus, as well as differences in the incidence of polyploidy and genome size differentiation between annual and perennial species, align with the general patterns observed in angiosperms. Methods We estimated the relative genome size (RGS) of over 3300 populations of 219 species from all 21 sections of Euphorbia subgen. Esula. We established new chromosome counts for 41 species and supplemented these with published chromosome numbers. Statistical analyses were performed on the elevational and latitudinal distributions of diploid and polyploid populations. We further investigated the RGS differentiation between annual and perennial species. Finally, we reconstructed the evolutionary dynamics of RGS across the phylogeny of the subgenus Esula. Key Results We identified an uneven frequency of polyploidy across different lineages of Euphorbia subgen. Esula, but a similar incidence of putative auto- and allopolyploids. Substantial evolutionary down- and upsizing of RGS was mostly driven by transitions to an annual or perennial life cycle, and to a lesser extent by polyploidy. Annual species have a smaller genome size, but the same probability of being polyploid as perennials. Polyploids thrive better at higher latitudes, but at lower elevations, which is consistent with general patterns observed across angiosperms. Conclusions Our large-scale study provides evidence that multiple polyploidization events at different temporal scales have triggered diversification within the highly diverse genus Euphorbia, and that the spatial distribution of diploid and polyploid populations follows the general patterns revealed for flowering plants.