## 4 Discussion  
Resolving the phylogenetic relationships for _Crepis_ provided the evolutionary framework for elucidating the evolution of the chromosome numbers and karyotype structure. Phylogeny based on the biparentally inherited nrITS of mostly diploid species of _Crepis_ was found to be largely congruent with previously published results (Figure S1; [22; 23]). In the present study, a new clade comprising species of the North American _Crepis_ agamic complex was identified. These species have not been included in previous analyses. The phylogenetic relationships inferred in this study were inconsistent with the sections defined by [PERSON] [20], in agreement with the earlier phylogenetic analyses [22]. Each clade and subclade contained species previously classified in different Babcock sections (Figure S1). A phylogenetic analysis, based on the chloroplast markers, recovered mostly the same main groups of species as the nrITS-based analyses. However, the relationships among these clades were found to be incongruent between the nuclear and plastid markers. Such nucleo-cytoplasmic discordance has been well documented in previous studies of higher plants [49]. This incongruence could be explained by the convergent evolution of shared chloroplast sequences, incomplete lineage sorting of the ancestral polymorphisms, or intra-gressive hybridization [50; 51]. The _Crepis_ species analysed here were mostly diploids, but because _Crepis_ species are primarily cross-pollinated and many of them hybridise extensively [20], introgression could have accompanied the speciation of individual species, as also suggested for other plant groups [52; 53]. The incongruence could be also explained by technical reasons. Several nodes in nrITS phylogram in clade 4 were weakly supported and the analysed species represent only a quarter of the _Crepis_ genome, which may influence the results. The incongruence between the nrITS and cpDNA trees concerning the position of _C. biennis_ could suggest its allopolyploid origin. _C. biennis_ is an octopolid species [47] whose origin and parental species are not yet known. The present analysis suggests a putative ancestral species for the two subgenomes of this polyploid taxon, species that are similar to the extant _C. nicaensis/C. setosa_ and another species related to _C. tectorum_ (Figure 1). Additional molecular phylogenetic and cytogenetic studies are necessary to elucidate the origin of _C. biennis_. This study reports the genome sizes for 33 species of _Crepis_ s.l., eight of them for the first time. The genome sizes that were reported in the current study are largely in agreement with previous reports, except for two species: _C. vesiaria_ and _C. panmonica_ (Table 2; [12; 54; 55]). This discrepancy is probably the result of methodological factors as the previous data were obtained using Feulgen densitometry or flow cytometry but with different standards. In the case of the diploid _C. vesiaria_, the discrepancy (2.43 pg/1C in this study versus 4.18 reported by [PERSON] et al. [12]) could result from the presence of the diploid and polyploid cytotypes within this species [20]. A strong correlation between genome size and life form has been suggested for _Crepis_ in previous studies [12]. The current results, however, did not show an obvious correlation between these two characters. Both annual and perennial _Crepis_ species groups showed high levels of variation of their genome sizes. Both one of the smallest (_C. leontodontoides_ 1.06 pg/1C) and the largest genomes (_C. lacera_; 7.46 pg/1C) were found in the perennial diploid species. The correlation between genome size and plant life form has been extensively discussed in the literature. The annual life form, especially in woody species, was inferred to be associated with a smaller genome size compared to its related perennials [56; 57; 58]. Such a correlation, however, must be interpreted with caution because other ecological and evolutionary factors might also influence genome size evolution [59].