Abstract Chromosome numbers for 16 Hieracium s.str. species from Bosnia and Herzegovina, Bulgaria, Macedonia, Montenegro, Poland, Romania and Serbia are given and their metaphase plates are illustrated. Chromosome numbers are published for the first time for H. filarszkyi Jáv. & Zahn 2n = 3x = 27, H. fritschianum Hayek & Zahn 2n = 3x = 27, H. fritzeiforme Zahn 2n = 3x = 27, H. hercegovinicum (Freyn & Vandas) Szeląg 2n=3x=27, H. nivimontis (Oborny & Zahn) Chrtek fil. 2n = 4x = 36, H. vagneri Pax 2n = 4x = 36, as well as three undescribed species of hybrid origin between H. olympicum Boiss. and H. sparsum Friv. 2n = 4x = 36, H. naegelianum Panc. and H. scardicum Bornm. & Zahn 2n = 3x = 27, and H. transylvanicum Heuff. and H. umbellatum L. 2n = 4x = 36.

Abstract Chromosome numbers for 12 Hieracium s.str. species from Bulgaria, Macedonia, Montenegro, Poland, Romania and Serbia are given and their metaphase plates are illustrated. Chromosome numbers are published for the first time for H. albinum Fries 2n=4x=36, H. bukovicae Rohlena & Zahn; 2n=3x=27, H. retyezatense subsp. subatratiforme Neičeff & Zahn 2n=4x=36, H. velenovskyi Freyn 2n=3x=27, as well as two undescribed species belonging to the H. bohatschianum agg. 2n=4x=36 and H. nigrescens agg. 2n=4x=36 and a hybrid between H. naegelianum Pančić and H. bifidum s.lat. 2n=4x=36.