Occurrence and habitat preferences of diploid and tetraploid cytotypes of Centaurea stoebe in the Czech Republic.

Two ecologically and phenotypically distinct cytotypes, a diploid and tetraploid, are known in Centaurea stoebe. Diploids are widespread throughout Europe and occur mainly in semi-natural habitats (dry grasslands, rocky ledges, etc.). Tetraploids are probably native in south-eastern Europe and spreading in central and western Europe, where they frequently occur in man-made habitats (roads and railways, stone quarries, etc.). Tetraploids occur also in North America, where they rank among the most noxious invasive plants. Despite good knowledge on various life history traits and the invasiveness of tetraploids, detailed information on the distribution of cytotypes in its native range in Europe is still fragmentary and there is no karyological data on C. stoebe occurring in the Czech Republic. Using flow cytometric screening of 119 populations, we report for the first time the occurrence of both cytotypes in the Czech Republic and describe their habitat preferences. Diploids (94 localities) were more frequent than tetraploids (25 localities). Habitat preferences of the cytotypes confirmed the situation reported from other parts of central and western Europe: diploids markedly prevail in semi-natural habitats whereas tetraploids occupy mainly man-made habitats. The C. stoebe cytotypes can be distinguished as distinct subspecies and should be added to the current list of the Czech flora.