Chromosome numbers are given for 16 taxa (and one interspecific hybrid) of Hieracium subgen. Pilosella originating from Central Europe: H. apatelium Nägeli et Peter (2n = 45), H. aurantiacum L. (2n = 36), H. bauhini Besser (2n = 36, 45, 54), H. brachiatum Bertol. ex DC. (2n = 45, 48, 63, 72), H. densiflorum Tausch (2n = 36), H. echioides Lumn. (2n = 18, 27, 36), H. floribundum Wimm. et Grab. (2n = 36, 45), H. glomeratum Froel. (2n = 36, 45), H. guthnickianum Hegetschw. (2n = 54), H. lactucella Wallr. (2n = 18), H. onegense (Norrl.) Norrl. (2n = 18), H. pilosella L. (2n = 36, 45, 54), H. piloselliflorum Nägeli et Peter (2n = 36, 45), H. piloselloides Vill. (2n = 36), H. rothianum Wallr. (2n = 36), H. schultesii F. W. Schultz (2n = 45), and the hybrid H. floribundum × H. aurantiacum (2n = 36). New chromosome numbers are reported for H. brachiatum and H. floribundum. The octoploid cytotype (2n = 72), recorded in H. brachiatum, is the highest ploidy level ever found in plants from the subgen. Pilosella originating from the field. Aneuploidy, rare in this subgenus in Europe, occurs in this hybridogenous species as well: it was recorded in one plant (2n = 48) collected in a hybrid swarm H. pilosella × H. bauhini. The breeding system in H. bauhini, H. brachiatum, H. densiflorum, H. echioides, H. pilosella, H. piloselloides, and H. rothianum was studied. The sexual reproduction of pentaploid H. pilosella is a new observation: it means an increase of diversity in possible reproduction modes of those cytotypes having odd chromosome numbers.
Chromosome numbers (ploidy levels) were recorded in the following 25 taxa of Hieracium subgen. Pilosella: H. arvicola Nägeli et Peter (2n = 45), H. aurantiacum L. (2n = 36, 45), H. bauhini Besser (2n = 36, 45), H. bifurcum M. Bieb. (2n = 45), H. brachiatum Bertol. ex DC. (2n = 36, 45), H. caespitosum Dumort. (2n = 36), H. cymosum L. (2n ~ 4x), H. densiflorum Tausch (2n = 36, ~ 4x), H. echioides Lumn. (2n = 18, 45), H. fallacinum F. W. Schultz (2n = 36, 45), H. floribundum Wimm. et Grab. (2n = 36, ~ 4x, 45,), H. glomeratum Froel. in DC. (2n = 45), H. iseranum Uechtr. (2n = 36), H. kalksburgense Wiesb. (2n ~ 5x), H. lactucella Wallr. (2n = 18), H. macranthum (Ten.) Ten. (2n = 18), H. onegense (Norrl.) Norrl. (2n = 18), H. pilosella L. (2n = 36, 45, 54), H. piloselliflorum Nägeli et Peter (2n = 45), H. pilosellinum F. W. Schultz (2n = 36, 45), H. piloselloides Vill. (2n = 27, 36, ~ 4x, 45, ~ 5x), H. pistoriense Nägeli et Peter (2n = 27), H. rothianum Wallr. (2n ~ 3x), H. schultesii F. W. Schultz (2n = 36, 45, ~ 5x), H. zizianum Tausch (2n = 27, 36, 54), and one hybrid, H. onegense × H. pilosella (2n = 36). Besides chromosome counts in root-tip meristems, flow cytometry was used to determine the DNA ploidy level in 83 samples of 9 species. The presence of a long marker chromosome was confirmed in tetraploid H. caespitosum and H. iseranum, in pentaploid H. glomeratum, and in both tetraploid and pentaploid H. floribundum. The documented mode of reproduction is sexual (H. densiflorum, H. echioides, H. piloselloides) and apomictic (H. brachiatum, H. floribundum, H. pilosellinum, H. piloselloides, H. rothianum, H. zizianum). Hieracium bifurcum and H. pistoriense are sterile. The chromosome number and/or mode of reproduction of H. bifurcum (almost sterile pentaploid), H. pilosellinum (apomictic pentaploid), H. piloselloides (apomictic triploid), H. pistoriense (sterile triploid), H. rothianum (apomictic triploid) and H. zizianum (apomictic triploid) are presented here for the first time. The sexual reproduction recorded in the pentaploid H. echioides is the second recorded case of this mode of reproduction in a pentaploid cytotype of Hieracium subgenus Pilosella. A previously unknown occurrence of H. pistoriense (H. macranthum – H. bauhini) in Slovakia is reported.
The few attempts to produce artificial hybrids in the genus Hieracium s. str. have usually failed due to the use of polyploid parental taxa reproducing via agamospermy. Presented here for the first time are data on artificial hybridization in Hieracium s. str. which may help in understanding the microevolutionary processes resulting in the great morphological and genetic diversity in this genus. Diploid, sexually reproducing species (H. alpinum, H. pojoritense, H. transsilvanicum and two stable morphological types of H. umbellatum – of a low altitude and a high mountain type) were used as parent plants in experimental crosses. In most cases true hybrids, with intermediate morphology, were obtained. All the hybrids tested were diploid and produced a high amount of stainable pollen (65–92%). Hybrid progeny resulting from one cross exhibited a large range of morphological variation due to the combination of alleles from unrelated parental species. The percentage of welldeveloped achenes per capitulum, in capitula with at least one well-developed achene, in hybrids, ranged from 1.9 to 12.5% after free or controlled pollination, with an average of 4–5% per capitulum. Similar results (1.9–12.1%) were obtained from triple-cross hybrids. However, most of the capitula of hybrid progeny (either F1 or triple) were completely sterile after free or controlled pollination. Sterility is probably caused by genome incompatibility of unrelated parental taxa belonging to different sections. In two crosses, where strictly allogamous diploid plants of H. umbellatum (both morphotypes) were used as mother plants and F1 hybrids as pollen donors, some matroclinal progeny were obtained. This is a further example of the previously reported mentor effect. Diploid hybrids may be involved as pollen donors in gene flow as they produce uniformly sized and viable pollen. They are probably substantially less important as seed parents.
A taxonomic concept for the Hieracium nigrescens agg. (H. alpinum ≥ H. murorum) in the Western Carpathians is proposed. Three taxa at the species level are recognized, i.e. Hieracium jarzabczynum, H. mlinicae and H. vapenicanum. One new combination, Hieracium mlinicae (Hruby et Zahn) Chrtek f. et Mráz (H. nigrescens subsp. mlinicae Hruby et Zahn) is published. All taxa should be considered as endemic to the Western Carpathians (both the Polish and Slovakian parts). Detailed descriptions, drawings, lists of localities, distribution maps and determination key are provided along with a comparison with the last comprehensive account of the group (by Zahn 1936). Several lectotypes were chosen for the taxa recognized by Zahn within H. nigrescens s.l.
A taxonomic study of the Pilosella alpicola group growing in the Carpathians revealed the presence of two morphologically distinguishable taxa: P. ullepitschii (Błocki) Szeląg and P. rhodopea (Griseb.) Szeląg. While P. ullepitschii is endemic to the Carpathians, P. rhodopea is a Balkan subendemic with two isolated localities in the Southern Carpathians (Mt Cozia and Mt Zmeuretu). The core area of distribution of P. ullepitchii is the natural subalpine and alpine meadows of the Western Carpathians (the Vysoké and Západné Tatry Mts in Slovakia and Poland). In addition, only three isolated localities are known from the Nemira Mts (Romanian Eastern Carpathians) and one from the Bucegi Mts (Romanian Southern Carpathians). Interestingly, the Romanian populations occur in man-made habitats (secondary pastures). Karyological and flow cytometric analyses of 305 plants from 13 populations of P. ullepitschii revealed only diploid plants (2n = 2x = 18). One Carpathian population of P. rhodopea from Mt Cozia is also diploid. This is the first report of diploidy in this species. However, the populations from the main part of the distribution of this taxon in the Balkan mountains include other cytotypes. Detailed morphological descriptions and distributions for both taxa are given.