Cytomorphological studies on American and European Phleum commutatum Gaud. [Poaceae]

The morphology, karyotype structure and nuclear DNA amount of European and American representatives of alpine cat's-tail Phleum commutatum Gaud. were analysed. The evolutionary relationships within this group of taxa are discussed. It was shown that the American and European tetraploids are both morphologically and karyologically similar to each other and to the diploid race of this species from the Polish Carpathians. Diploid relatives of tetraploid P. commutatum i.e., P. commutatum (2x) and P. rhaeticum (Humphries) Rauschert, showed intra- and interspecific differences in nuclear 2C DNA values, whereas tetraploids (of both European and American origin) showed highly uniform nuclear DNA amounts. The 2C DNA uniformity and the greater mean size of the basal chromosome set in tetraploid P. commutatum as compared with its diploid relatives suggest that the change in genome size occurred during early evolution of the tetraploid race of P. commutatum, before its migration to America.