Figure 2: Population genomics of silver birch and Betulaceae relatives.

(a) Dispersion of 80 silver birches sampled from 12 sites across most of the geographic range of B. pendula. Populations are plotted with dots color-coded based on dispersion by latitude and longitude. ADMIXTURE analysis of SNP variation (superimposed with bar plots; center line, median; box, interquartile range; whiskers, 1.5× interquartile range; points, outliers) shows that Finland is a mixing zone between European (blue) and Asian (green) source populations. Samples from Ireland were highly admixed with other birch species and/or polyploid and were removed from the analysis. Source: OpenStreetMap contributors. (b) PCA shows clear separation between B. pendula populations and other sampled birch species (open circles). Eight B. pendula individuals (gray shading) were putative polyploids or interspecies admixed individuals. These included all Irish individuals and two individuals from Punkaharju, Finland. The main B. pendula population formed a cline along PC2 (purple shading). Fin: Finland, Sco: Scotland.