Meiotic studies on 26 taxa, including two hybrids, of the genusCarexare presented. Results obtained with the hybrid betweenCarex remotaandCarex paniculatassp.lusitanicawere remarkable, since they showed a great number of configurations and even different chromosome numbers in metaphase I. The karyology of theCarex muricatagroup in the SW of Europe was studied for the first time. I also performed the first studies on the karyology of two species belonging to sectionCarexin the SW of Europe, namelyCarex hirta, which gave the highest chromosome number reported so far for the genusCarex(2n = 114), andCarex lasiocarpaErhr., for which I found a putative triploid whose chromosome number (2n = 78–85) was not constant in metaphase I. Agmatoploidy seems to be the most important process involved in the cytogenetic evolution of the species studied here. The idea of the existence of "fragile points" in the chromosomes is suggested to explain the formation of bivalents upon chromosome breakage. In addition, the chromosome number forCarex canariensisis reported here for the first time.Key words:Carex, Cyperaceae, cytogenetics, western Mediterranean.