Nuclear genome size (C-value) was determined by flow cytometry for 23 populations of 15 Crepis L. (Asteraceae) taxa originating from Turkey. Genome size of seven taxa are reported for the first time as well as two new chromosome counts. The 1C-value of the studied taxa ranges from 1.35 pg to 7.06 pg, which represents more than fivefold variation. There is a positive correlation between genome size and altitude. Genome size is not correlated with the chromosome number and sectional division of the studied taxa. Systematic and ecological significance of genome size are discussed within the framework of the results obtained in this study.