Genetic variation in British Campanula rotundifolia L.

The harebell (Campanula rotundifolia) is a short‐lived perennial native to the British Isles, where tetraploid, hexaploid and (rarely) pentaploid types occur. The hexaploid and tetraploid cytotypes show geographic separation; hexaploids are largely restricted to Ireland and the west coast of Britain. Here, we analyse morphometric and molecular genetic variation in harebell populations from across Britain and from three European locations, and assess quantitative genetic variation in phenology through a common garden trial, to determine levels of diversity and divergence, and test whether phenotypic divergence is associated with geographic variation in environment. Morphometric analysis resolves tetra‐ and hexaploids. Molecular data supported the separation of the cytotypes, with unique chloroplast DNA haplotypes in each cytotype and nuclear ITS data showing a single haplotype for hexaploids but numerous haplotypes in tetraploids. The molecular divergence between cytotypes suggests possible different origins and invasion pathways since the last glacial maximum.