rDNA-FISH pattern in selected <i>Hieracium</i> species representing different ploidy levels

Polyploid species of Hieracium s.str. are near-obligatory apomicts capable of producing non-reduced pollen grains and intrageneric crossing with sexual diploid species. Most probably, such a mating system leads to the emergence of separate lineages of apomictic plants with increased ploidy levels, each of which has a complete set of genomes of its putative (most probably triploid) apomictic parent. The correct identification of such lineages could facilitate taxonomic and phylogenetic research in Hieracium. In this paper, we analyzed the distribution of the 5S and 45S rDNA segments in the karyotypes of six selected Hieracium taxa, representing all ploidy levels reported in the genus: H. alpinum 2x, H. alpinum 3x, H. schustleri 4x, H. chrysostyloides 5x (H. sect. Alpina) and H. bifidum 3x, H. levicaule 3x (H. sect. Bifida). The analyzed rDNA markers suggest that two taxa of the higher ploidy level (4x and 5x) belonging to H. sect. Alpina inherited three genomes from the triploid H. alpinum, which has 2:1 genomic composition with two genomes from diploid H. alpinum and one genome with an untypical 5S rDNA-bearing chromosome of unknown origin. H. bifidum and H. levicaule differ from each other in the rDNA distribution pattern, which suggests that H. sect. Bifida may be a less homogenous group of species.