Chromosome numbers of 46 Hieracium L. and Pilosella Vaill. taxa from Austria, Bulgaria, Czech Republic, Macedonia, Montenegro, Poland, Romania, Serbia and Slovakia are presented. Chromosomes numbers are given for the first time for Hieracium amphigenum Briq. 2n = 3× = 27, H. bohatschianum Zahn 2n = 4× = 36, H. borbasii R. Uechtr. 2n = 4× = 36, H. cernuum Friv. 2n = 2× = 18, H. hazslinszkyi Pax 2n = 3× = 27, H. mirekii Szeląg 2n = 4× = 36, H. polyphyllobasis (Nyár. & Zahn) Szeląg 2n = 3× = 27, H. porphyriticum A. Kern. 2n = 4× = 36, H. racemosum Waldst. & Kit. ex Willd. subsp. racemosum 2n = 3× = 27, H. scardicum Borm. & Zahn 2n = 4× = 36, H. sparsum subsp. ipekanum Rech. fil. & Zahn 2n = 4× = 36, H. sparsum subsp. peristeriense Behr & Zahn, H. sparsum subsp. squarrosobracchiatum Behr & al. 2n = 3× = 27, H. tomosense Simk. 2n = 4× = 36, H. tubulare Nyár. 2n = 4× = 36, H. werneri Szeląg 2n = 3× = 27 and Pilosella fusca subsp. subpedunculata (Zahn) Szeląg, as well as five species of Hieracium sect. Cernua R. Uechtr. not described to date and a hybrid between H. bifidum s. lat. and H. pojoritense Woł
Chromosome numbers for 15 taxa of Hieracium L. s.str. from Bulgaria, Greece, Macedonia, Poland, Romania
and Slovakia are given and their metaphase plates are illustrated. Chromosome numbers are published for the
first time for H. vagneri Pax s.str. (2n = 4x = 36), H. wiesbaurianum subsp. herculanum Zahn (2n = 4x = 36),
H. wiesbaurianum subsp. kelainephes Nyár. & Zahn (2n = 3x = 27), as well as for two undescribed species
of hybrid origin between H. umbellatum L. and H. wiesbaurianum s.lat. (2n = 3x = 27), and between H. sparsum
Friv. and H. schmidtii s.lat. (2n = 3x = 27), and for three undescribed species of the H. djimilense agg.
(2n = 3x = 27), H. heldreichii agg. (2n = 3x = 27), and H. sparsum agg. (2n = 3x = 27). Furthermore, the chromosome
numbers of two undescribed species of hybrid origin between H. umbellatum L. and H. wiesbaurianum
s.lat. (2n = 3x = 27), and between H. sparsum Friv. and H. schmidtii s.lat. (2n = 3x = 27) are given. A new,
tetraploid chromosome number is given for H. barbatum Tausch from the northernmost locality of the species
in Europe.
Chromosome numbers for 15 taxa of Hieracium s.lat. (including two taxa of Pilosella Vaill.) from Bosnia and Herzegovina, Bulgaria, Greece, North Macedonia, Poland, Romania and Slovakia are given and their metaphase plates are illustrated. Chromosome numbers are published for the first time for H. pannosum subsp. parnassi Nägeli & Peter from Greece (3x and 4x), and for an undescribed species of H. sect. Cernua from North Macedonia (4x). A new, diploid chromosome number was found in H. bracteolatum s.lat. from Greece.
Chromosome numbers for 23 taxa of Hieracium L. from Bulgaria, Greece, Poland and Slovakia are given and their metaphase plates are illustrated. The ploidy level of 8 taxa was also confirmed by flow cytometry. Chromosome numbers are published for the first time for Hieracium bracteolatum subsp. koracis (Boiss.) Zahn (4x), H. marmoreum Pančić & Vis. (3x), H. ossaeum Zahn (3x), H. sartorianum Boiss. & Heldr. (3x), H. sericophyllum Nejčeff & Zahn (3x) as well as for five other undescribed species.
The authors report the first discovery of diploid populations of Hieracium naegelianum Panč. subsp. naegelianum and H. naegelianum subsp. ljubotenicum Behr & Zahn., and give the first chromosome counts for H. cernuum Friv., H. gymnocephalum Griseb. ex Pant., H. sparsum Friv., Pilosella pavichii (Heuff.) Holub and P. serbica (F. W. Schultz & Schultz-Bip.) Szeląg from Macedonia and/or Montenegro. A diploid chromosome count for Hieracium renatae Szeląg is confirmed based on material from the whole distribution range of the species. An emasculation experiment showed that all the analyzed diploid Hieracium taxa reproduce sexually.