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Given the paucity of information about genome size in the genus Centaurea, nuclear DNA content of 15 Centaurea taxa, belonging to four subgenera and six different sections, has been investigated for the first time. The sample concerns 21 populations from the Dalmatia region of Croatia. The 2C DNA content and GC percentage were assessed by flow cytometry and chromosome number was determined using standard methods. Genome size of studied Centaurea ranged from 2C=1.67 to 3.72 pg. These results were in accordance with chromosome number and especially with ploidy level that varies throughout this group; 2C DNA values ranged from 1.67 to 3.43 pg for diploid, and from 3.19 to 3.72 for polyploid taxa. No significant intraspecific variations of DNA amount were found between two subspecies of C. visiani and C. ragusina, nor between two varieties of C. gloriosa. However, some populations of C. glaberrima and C. cuspidata showed a significant difference in DNA amount. Three different basic chromosome numbers were observed in studied species (x=9, 10, and 11). The most frequent basic number was x=9. C. rupestris, C. ragusina ssp. ragusina, and C. r. ssp. lungensis possessed x=10 and C. tuberosa x=11. The species with a basic chromosome number of x=9 had a small genome size and the smallest chromosomes (on average 0.09 to 0.12 pg/chromosome) but frequently present polyploidy. Centaurea ragusina ssp. ragusina and C. r. ssp. lungensis had a mean base composition 41.3% GC.

This work focuses on the representatives of genus Echinops (Asteraceae, Cardueae) in the Aegean and Balkan regions, from the perspective of their genome evolution. Chromosome numbers were determined by orcein staining in 14 populations of nine taxa, and DNA contents were assessed by flow cytometry in 24 populations of nine taxa. A molecular phylogeny based on the internal transcribed spacer (ITS) and trnL-trnF and including first sequences for two taxa (Echinops sphaerocephalus subsp. taygeteus and E. spinosissimus subsp. neumayeri) provided a framework for discussing genome changes. From a methodological point of view, similar C-DNA value estimates were obtained when measuring, for a same population, fresh leaves from adult plants collected in the field and from cultivated seedlings. Conversely, despite giving the appearance of being correct (e.g., low coefficient of variation), genome size assessed using silica gel-preserved material differs significantly from values obtained for the same populations with fresh material. Nevertheless, silica gel-preserved material may still provide rough estimates of genome size for, e.g., inferring ploidy level. Suitablenon-silica gel-based-DNA amounts assessed for 23 populations range from 2C = 6.52 pg (E. spinosissimus subsp. neumayeri) to 2C = 9.37 pg (E. bannaticus). Chromosome counts were established for the first time for Echinops graecus (2n = 32), E. sphaerocephalus subsp. albidus (2n = 32), E. sphaerocephalus subsp. taygeteus (2n = ca. 30), and E. spinosissimus subsp. neumayeri (2n = 28). Genome size and chromosome number are confirmed as crucial parameters for deciphering lineage diversification within the genus Echinops.

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