Genome doubling and changes in genome size are fundamental evolutionary processes, with polyploidy being one of the most important forces influencing plant diversification. However, little is currently known about the extent of genome size variation within taxa and the evolutionary forces acting on this variation. Arabidopsis kamchatica has been reported to contain both diploid and tetraploid individuals (2 or 4 copies of every chromosome). In a new study in AoB PLANTS, Wolf et al. found genome size differences among populations, and among populations genome size varied by 7%. However, all sampled A. kamchatica plants from a wide geographic range were tetraploids. This level of intraspecific genome size variation in A. kamchatica is lower than in other Arabidopsis taxa. Due to its close relationship to A. thaliana, A. kamchatica has the potential to be very useful in the study of polyploidy and genome evolution.