Despite the substantial knowledge of the variation in cytotypes at large spatial scales for many plants, little is known about the rates at which novel cytotypes arise or the frequencies and distributions of cytotypes at local spatial scales. The frequency distribution, local spatial structure, and role of habitat differentiation of tetra-, penta- and hexaploid cytotypes of the bulbous geophyte Allium oleraceum were assessed in 21 populations sampled in the Czech Republic. The ploidy levels determined by flow cytometry confirmed that there was a mixture consisting of two or three cytotypes (i.e. 4x+5x, 4x+6x, 5x+6x, 4x+5x+6x). In addition, mixtures of cytotypes were found at sites previously considered to be cytotype-homogeneous. At all sites previously found to contain a mixture of two cytotypes, no plants with the third ploidy level were found. Although the relative frequencies of cytotypes varied considerably both among and within populations, mixed populations consisting of tetra- and hexaploids were usually dominated by tetraploids. This suggests that there are secondary contacts among cytotypes but there is little gene flow among them except for the rare formation of hexaploids in tetraploid populations. Cytotypes were not randomly distributed over the study area but were spatially segregated at either 47.6% or 61.9% of the sites investigated, depending on the statistical test (Mantel test or average distance test) used. When the composition of habitats at each of the sites is taken into account, cytotypes were more frequently spatially segregated at sites with a heterogeneous environment than a homogeneous environment. This implies that the cytotypes are ecologically differentiated. The frequent co-occurrence of cytotypes, with or without significant spatial segregation, at many sites with heterogeneous or homogeneous environments, however, suggests that niche differentiation alone is probably ineffective in determining co-occurrence. It is supposed that the prevailing vegetative reproduction associated with local dispersal, a high population density of the species in a landscape, and non-equilibrial processes influencing the establishment and extinction of A. oleraceum populations can also support the local co-occurrence of cytotypes.
The agamosporous and taxonomically critical Dryopteris affinis group was investigated as part of a cytogeographic and morphometric study of ferns in Central Europe. Material from 27 localities in the Czech Republic, Slovakia, Poland and Austria was sampled and evaluated using both morphometric multivariate and karyological analyses. Chromosome counts and flow cytometric analyses revealed the existence of two distinct triploid taxa (2n = 123) of differing genome size, which correspond to D. borreri and D. cambrensis, and of a rare pentaploid hybrid (2n = 205) D. ×critica (D. borreri × D. filix-mas). Morphometric analyses confirmed a clear separation between both triploid taxa. New quantitative characters were selected based on a discriminant analyses, and a key for the identification of the species is presented.
We studied the agamic complex of Hieracium subgen. Pilosella in the Šumava/Böhmerwald, the borderland between the Czech Republic and Germany. Their DNA ploidy levels/chromosome numbers, breeding systems, chloroplast haplotypes as well as the clonal structure of apomicts were determined. The complex consists of the following basic and intermediate species and recent hybrids. Basic species: H. aurantiacum L. (tetraploid and pentaploid, both apomictic), H. caespitosum Dumort. (tetraploid, apomictic), H. lactucella Wallr. (diploid, sexual), H. pilosella L. (tetraploid, sexual); intermediate species: H. floribundum Wimm. et Grab. (tetraploid, apomictic), H. glomeratum Froel. (tetraploid and pentaploid, both apomictic), H. scandinavicum Dahlst. (tetraploid, apomictic); recent hybrids: H. floribundum × H. pilosella (partly corresponding to H. piloselliflorum – tetraploid and hexaploid; tetraploid sexual or apomictic), H. glomeratum × H.pilosella (aneuploid, 2n = 38), H. aurantiacum × H. floribundum (tetraploid, almost sterile or apomictic), H. lactucella × H. pilosella (H. schultesii, triploid sterile, tetraploid sexual), H. aurantiacum × H. pilosella (H. stoloniflorum, tetraploid, sexual), H. aurantiacum > H. pilosella (H. rubrum, hexaploid). The hexaploid hybrids between H. pilosella and H. floribundum or H. aurantiacum produced mainly polyhaploid progeny. Two trihaploid plants were found growing in the neighbourhood of their putative hexaploid maternal parent H. rubrum, which is the first record of polyhaploids of this subgenus in the field. Comparison with other mountain ranges (especially the Krušné hory/Erzgebirge, and Krkonoše) with an almost identical composition of basic species, revealed that the structure of the agamic complexes differ.
As a result of inconsistencies in morphological characters, Cerastium pumilum and C. glutinosum have been misunderstood or confused in many European floras since the 1960s. In the second volume of the Flora Nordica, a revised treatment of C. pumilum s.l. is provided and this concept is tested here for eastern Central European populations. The cytometric and morphological part of the study is based on living plants from 85 populations in the Czech Republic, Slovakia, Poland, Austria and Hungary. Flow cytometric analyses of the samples revealed two groups differing in ploidy level and corresponding to two cytotypes (a known octoploid, 2n ≈ 72, for C. glutinosum and yet unknown dodecaploid, 2n ≈ 108, for C. pumilum). Eleven morphological characters were scored or measured in plants of known ploidy level and the data set analysed using multivariate statistics (principal component analysis and canonical discriminant analysis); the two morphologically well-separated groups were identical with the two cytotype groups detected by flow cytometry. Based on these results, we suggest treating the detected cyto-morphotypes as the species C. pumilum and C. glutinosum. Our analysis further revealed that the traditionally used characters (glabrous vs. hairy adaxial surface and presence vs. absence of a scarious margin to the tip of the lowermost bracts) are not taxonomically informative. The characters best differentiating the species include indument on the lowermost vernal internodium, length of mature stylodia, length of glandular hairs on sepals and maximum diameter of mature seed. A key for identification of both species is also provided. A revision of almost 1600 specimens deposited in 16 Central European herbaria revealed that the species show different distribution patterns in Central Europe and partial habitat segregation. Specimens from the Czech Republic previously assigned to C. litigiosum were identified as C. pumilum; consequently, C. litigiosum must be removed from the Czech flora.
This paper reviews recent use of flow cytometry in studies on apomictic plant taxa. The most of apomictic angiosperms are polyploid, often differing in ploidy level from their sexual counterparts within the agamic complex. Flow cytometry is widely used for screening the ploidy levels of mature plants and their seed generated both in the field and in experiments. Routine ploidy screening often accompanied by molecular markers distinguishing individual genotypes are used to reveal novel insights into the biosystematics and population biology of apomictic taxa. Apomixis (asexual seed formation) is mostly facultative, operating together with other less frequent reproductive pathways within the same individual. The diversity in modes of reproduction in apomicts is commonly reflected in the ploidy structure of their progeny in mixed-cytotype populations. Thus, flow cytometry facilitates the detection and quantification of particular progeny classes generated by different reproductive pathways. The specific embryo/endosperm ploidy ratios, typical of the different reproductive pathways, result from modifications of double fertilization in sexual/apomictic angiosperms.Thus, the reproductive origin of seed can be identified, including autonomous or pseudogamous apomixis, haploid parthenogenesis and sexual reproduction, involving either reduced or unreduced gametes. Collectively, flow cytometry has been used to address the following research topics: (i) assessing the variation in ploidy levels and genome sizes in agamic complexes, (ii) detection and quantification of different reproductive modes in facultative apomicts, (iii) elucidation of processes in populations with coexisting sexual and apomictic biotypes, (iv) evolution of agamic complexes, and (v) genetic basis of apomixis. The last topic is of paramount importance to crop breeding: the search for candidate gene(s) responsible for apomixis is the main objective of many research programmes. A list of the angiosperm taxa that could provide model systems for such research is provided.