Knowledge of evolution of genome size in species with holocentric chromosomes is limited. Lipnerová et al. study genome size and base composition in the holocentric genus Carex (Cyperaceae) in relation to chromosome number. They find that genomes are relatively small and very GC-poor compared with other angiosperms, with genome size positively correlated with GC content and negatively correlated with chromosome number. They identify seven polyploid and two potentially polyploid species in Carex subgenus Carex, and determine that this subgenus exhibits larger genome sizes and a higher rate of genome size evolution compared to subgenus Vignea. They conclude that evolution of genomes and karyotypes in the Carex genus is promoted by frequent chromosomal fissions/fusions, rare polyploidy, and common repetitive DNA proliferation/removal.