Hieracium racemosum in the Czech Republic

The distribution of Hieracium racemosum in the Czech Republic was studied based on herbarium specimens deposited in 22 public herbaria. This species, classified within H. sect. Italica, is one of 58 native hawkweeds (Hieracium s. str.) of the Czech flora. From H. sabaudum, the most similar species, it may be distinguished by usually shortly petiolate lower stem leaves, racemous to paniculate synflorescence, rather long inner involucral bracts, which are dark to pale green and have a light green margin, as well as by yellowish or grey, rarely red to chestnut-brown achenes and usually dentate (non-fimbriate) receptacle pits. The leaf arrangement, i.e. the concentration of leaves in the middle or lower third of the stem, frequently used as the main character to distinguish H. racemosum from H. sabaudum, has only limited diagnostic value. Traditionally, six subspecies are reported from the Czech Republic, with most Czech populations of H. racemosum assigned to H. racemosum subsp. barbatum and subsp. racemosum. Using flow cytometry measurements and chromosome counts, three plants originating from two populations from the south-eastern parts of Czechia were assessed to be triploid (2n ~ 3x) and one plant had a chromosome number of 2n = 27, respectively. We revised 541 herbarium specimens of this species collected in the country, of which 432 (i.e. about 84%) were originally identified correctly (including taxonomic synonyms). However, another 400 specimens originally identified as H. racemosum were revised as H. sabaudum (97%) or H. umbellatum (3%). In the Czech Republic, most localities of H. racemosum are concentrated in Moravia (eastern part of the country). Isolated locations are found in eastern Bohemia and single outposts further towards the west. Based on the number of specimens revised, the distribution map presented here may be considered representative. The infraspecific taxonomy of H. racemosum and possible occurrence of H. neolatyphyllum in te Czech Republic require further research.