The occurrence and extent of genome size variation below the species level are currently poorly analysed. Using flow cytometry, Duchoslav et al. demonstrate complex patterns of holoploid and monoploid genome size variation both within and between six ploidy levels of Allium oleraceum (Alliaceae) for 114 populations across the European continent. They consider that these are most likely the result of several interacting factors, including different evolutionary origins of cytotypes via hybridization of parental combinations with different genome sizes in the south-western and south-eastern part of Europe, introgression between cytotypes, and anthropic dispersal. The role of broad-scale environmental variables in shaping the genome size is probably of minor importance in A. oleraceum.
Genome size is known to affect various plant traits such as stomatal size and seed mass but these associations are not well understood for species with very large genomes, which are largely represented by geophytic plants. Veselý et al. survey genome size across 219 geophytes and find that it is associated with species’ ecology and phenology, and analysis also shows an association with changes in DNA base composition. They suggest that although production of larger cells appears to be an advantageous strategy for fast development in seasonal habitats, the drought sensitivity of large stomata may restrict the occurrence of geophytes with very large genomes to regions not subject to water stress.