Cover illustration: The inset cover image shows part of the distribution of mixed ploidy populations of diploid (2x), triploid (3x) and tetraploid (4x) cytotypes of Tripleurospermum inodorum (Asteraceae) in central Europe. The contact zone between the diploid and tetraploid cytotypes has a diffuse, mosaic-like structure enabling common cytotype coexistence and inter-ploidy mating. This leads to striking variation in DNA content among offspring from the within-population to the landscape level, and high potential to generate cytogenetic novelty, and may facilitate inter-ploidy gene flow. See Čertner et al. (pp. 303–315)