Out of 94 grass genera with 318 species in Bulgaria, 294 species and 60 subspecies are studied karyologically on the basis of 722 populations. Hybridization, polyploidy and to a lower extent apomixis and aneuploidy, restricted to dysploidy are the evolutionary mechanisms acting within the grass family in Bulgarian flora. Sixteen polyploid or polyploidaneuploid series have been established which reveals the process of local speciation, particularly in the genera ofElymus, Bromus, Brachypodium, Poa, Festuca, Avena, Koeleria, StipaandSesleria.The diploid level is presented by 305 cytodemes, tetraploids are 234, hexaploids - 80, octoploids - 16 and decaploids - 10. The percentage of grass polyploidy ranks 56.50%, mainly consisted of tetraploids - 72.45%.