Nuclear genome size, as measured by flow cytometry with propidium iodide, was used to investigate the relationships within the genus Gagea (Liliaceae), mainly from the Netherlands. The basic chromosome number for Gagea is x = 12. The inferred ploidy in the Dutch and German accessions varies from diploid to decaploid. Consequently there is a large range of genome sizes (DNA 2C-values) from 14.9 to 75.1 pg. Genome sizes are evaluated here in combination with the results of morphological observations. Five species and the hybrid G. × megapolitana are reported. Apart from 14 diploid G. villosa , six plants of G. villosa with an inferred tetraploidy were found. For the 186 Dutch accessions investigated 85 turned out to be the largely sterile G. pratensis (inferred to be pentaploid). Inferred tetraploid and hexaploid G. pratensis were found in 30 and 20 localities, respectively. In one locality an inferred decaploid (10×) plant was found that could represent a doubled pentaploid G. pratensis . An inferred decaploid G. pratensis was never reported before. The genome size of Gagea × megapolitana from Germany fitted with its origin as a cross between the two hexaploids G. pratensis and G. lutea . Gagea spathacea from the Netherlands was inferred to be nonaploid as was recorded from plants across Europe. The aim of the study was to use flow cytometry as a tool to elucidate the taxonomic position of the Dutch Gagea .