In this study, we report the somatic chromosome numbers (2n) of 31 taxa belonging to Asteraceae, Brassicaceae, Poaceae, Hypericaceae, Lamiaceae, Fabaceae and Plantaginaceae families from wetlands of Hamadan region in Iran. The chromosome numbers of about half of these species have not been reported in the previous literature. Chromosome number of Ononis spinosa counted chromosomally for the first time at the world level and the chromosome numbers of Erigeron acer, Pulicaria dysenterica, Arctium lappa, Xanthium strumarium, X. spinosum, Barbarea plantaginea, Brachypodium sylvaticum, Polypogon fugax, Prunella vulgaris and Lathyrus chloranthus, are here reported for the first time from Iran. In all taxa 2n was 12, 14, 16, 18, 20, 24, 28, 30, 32 and 42, as a diploid, tetraploid and hexaploid levels. These newly available data are further compared with those previously published for the same or related species.