Figure 2.

Genetic admixture among the three native Betula species in Britain, with locations of populations tested, and pollen fossil sites. (A) Sharing of microsatellite alleles among the three species B. nana,B. pubescens and B. pendula shown as a structure plot with K = 3 corresponding with the three species. Within each species grouping, populations are ordered by latitude, with more northerly populations to the left-hand side. Thin vertical lines above the structure plot indicate population divisions. Three known F₁ hybrid seedlings are shown on the far right: B. nana × B. pendula,B. nana × B. pubescens and B. nana × B. pubescens, respectively. (B–D) The locations of the sampled populations of B. nana,B. pubescens and B. pendula, respectively: pie charts show the mean proportion of individual genotypes in each population assigned to a particular lineage by structure, and pie chart size is proportional to the sample size for each population. The centre of pie charts represents approximately its sampling locality unless the pie chart is connected to its sampling locality by a straight line. (E) Pollen sites of Betula species across Britain. Red stars represent the pollen sites of B. nana and B. nana, and blue stars represent the pollen sites of Betula likely to be B. pubescens and B. pendula.