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.