Complex distribution patterns of di-, tetra- and hexaploid cytotypes in the European high mountain plant Senecio carniolicus Willd. (Asteraceae)

DNA ploidy levels were estimated using DAPI-flow cytometry of silica-dried specimens of the European mountain plant Senecio carniolicus (Asteraceae), covering its entire distribution area in the Eastern Alps (77 populations, 380 individuals) and the Carpathians (5 populations, 22 individuals). Large ploidy level variation (2x, 4x, 5x, 6x, and 7x cytotypes) was found in this species, which has for a long time been considered uniformly hexaploid. Hexaploids predominated in the Eastern Alps and was the only cytotype found in the Carpathians, while odd ploidy levels (5x, 7x) constituted a small fraction of the samples (<1.3%). Tetraploids occurred in two disjunct areas, which correspond with putative Pleistocene refugia for silicicolous alpine plants. A similar pattern is present in diploids, but with substantial parts of their distribution outside potential refugia. Cytotype mixture was detected in 22 populations, the majority comprising diploids and hexaploids. Intermediate ploidy levels were mostly absent in mixed populations, which suggests limited gene flow and the evolution of reproductive isolation. Significant and reproducible intra-cytotype variation in nuclear DNA content was observed. Higher genome size in western diploids might be due to ancient introgression with the closely related S. incanus or to different evolutionary pathways in the geographically separated diploids