Festuca subgen. Schedonorus is a group of broad-leaved fescues, which can be divided into two clades: European and Maghrebian. We employed fluorescent in situ hybridization —FISH— with probes specific for 5S and 35S ribosomal DNA and genome size estimation using flow cytometry to shed light on the determination of possible parental genomes of polyploid species of the Maghrebian clade. Our results indicate that octoploid F. arundinacea subsp. atlantigena probably originated from crossing of the tetraploids F. arundinacea subsp. fenas —2n = 4x = 28— and F. mairei —2n = 4x = 28— followed by whole genome duplication. However, a large reconstruction of karyotype and genome downsizing has been revealed. Similarly, hexaploid F. arundinacea subsp. corsica presumably resulted from the interspecific hybridization of the diploid F. pratensis and tetraploid F. arundinacea subsp. fenas. Several scenarios on the origin of decaploid F. arundinacea var. letourneuxiana are discussed. This study contributed to our knowledge on the phylogeny of broad-leaved fescues and provided new information on the karyotypes —chromosome numbers, ploidy levels and numbers and positions of rDNA loci— using FISH and genome size estimations using flow cytometry in selected taxa of this important grass genus.