The origin of the two common cultivars of Crocus, C. ‘Stellaris’ (2n = 2x = 10) and C. ‘Golden Yellow’ (2n = 3x = 14) was investigated by fluorescent in situ hybridization using both total genomic DNA and cloned DNA sequences as probes. The clear differentiation between the chromosomes after genomic in situ hybridization supports the proposals of a hybrid origin of the cultivars and shows that they have the same parental genomes originating from C. flavus (2n = 8) and C. angustifolius (2n = 12). C. ‘Stellaris’ has four chromosomes of C. flavus origin and six chromosomes of C. angustifolius origin. C. ‘Golden Yellow’ has eight chromosomes of C. flavus origin and six chromosomes of C. angustifolius origin. The number and location of 18S-5·8S-26S rRNA genes on the chromosomes of the hybrids and of the parental species agree with the results from the genomic probings. Hybridization to Southern membranes also supports the hybrid origin of C. ‘Golden Yellow’.