Merlíky (druhy rodu Chenopodium jsou převážně jednoleté byliny z čeledi merlíkovitých (Chenopodiaceae). Osidlují především narušovaná místa, kde nejsou omezovány konkurenčně silnějšími vytrvalými druhy a kde mají dostatek světla. Některé druhy merlíků jsou velmi hojné, jiné jsou k vzácné nebo dokonce v České republice ohrožené. K těm druhým patří např. merlík slanomilný (Ch. chenopodioides), m. hroznový (Ch. botrys), m. zední (Ch. murale), m. smrdutý (Ch. vulvaria) nebo m. městský (Ch. urbicum). and Species of the genus Chenopodium are mostly annual herbs belonging to the family Chenopodiaceae. They grow mainly on disturbed localities where competition with stronger perennial species is minimized and where they can find enough light. Some species of this genus are very common, others are very rare or even endangered in the Czech Republic (e.g. C. chenopodioides, C. botrys, C. murale, C. vulvaria or C. urbicum).
Pollen viability was analysed causally between and within Central European Cirsium species and their hybrids to determine (i) how frequently hybrids are fertile and produce viable pollen; (ii) how the pollen viability of hybrids and their parents are related and how this is affected by the genetic distance between parents; (iii) how species promiscuity relates to species pollen viability; (iv) to what extent the pollen viability of a hybrid may predetermine its frequency in nature; (v) how the pollen viability of a hybrid and sympatricity of its parental species are related; and (vii) how the frequency of females in populations of gynodioecious species may affect the observed pollen viability. Altogether, the viability of 656,363 pollen grains was analysed using Alexander’s staining (1185 flowers from 301 plants from 67 field populations of 13 pure species and 1693 flowers from 345 plants from 96 field populations of 16 natural hybrids). The particular characters potentially related with pollen viability were estimated using following methods: natural hybrid frequency and species interfertility (by herbarium data), genetic distance (by AFLP), sympatricity (in local scale based on herbaria and literature data; on a global scale using the similarity between digitized maps of natural ranges). The strengths of pre- or postzygotic isolation were estimated for hybridizing species pairs using geographical data and pollen viability analyses. All hermaphrodite plants of the Cirsium hybrids had viable pollen, generally at lower levels than those found in pure species. The pollen viability of a hybrid generally decreased with increasing genetic distance between the parents and when the parental species had lower pollen viability. The pollen viability was decreased in frequently hybridizing species where occasionally individuals of pure species morphology may show decreased pollen viability. In some instances these might represent some unrecognized hybrid backcrosses. In populations of gynodioecious species where females co-occurred, pollen viability (in hermaphrodites)was also lower, indicating some degree of inbreeding depression. Hybrids between sympatric species exhibited higher post-pollination isolation (decrease of pollen viability), which suggests that the reproductive isolation had been increased by natural selection (effect similar to the Wallace effect). The strength of the postzygotic barrier (based on pollen viability) was generally stronger than that of the prezygotic barrier (based on distribution overlap) in studied hybridizing species pairs.
Bílé Karpaty Mts harbour some of the most species-rich managed grasslands in Europe, which contain a number of rare and disjunctly distributed species. Besides specific local environmental factors, the long Holocene history may explain the uniqueness of these grasslands. However, historical interpretations of the palaeoecological evidence from the region are far from unequivocal. While palaeomalacological data indicate persistence of open habitats throughout the entire Holocene, fragmentary pollen data support the hypothesis of a medieval origin of the grasslands. This paper reviews the available phytogeographical, archaeological and palaeoecological knowledge that provides indirect evidence for a prehistoric origin of the grasslands in the Bílé Karpaty Mts. High concentration of rare heliophilous species with a disjunct distribution in the south-western part of the Bílé Karpaty Mts suggest their long-term persistence. The archaeological findings provide evidence for the existence of prehistoric human settlement in this region since the Neolithic (Middle Holocene). Direct evidence for the existence of open human-influenced habitats before medieval times, based on the results of a multi-proxy analysis (macrofossils, molluscs and pollen) of an organic sediment dated back to Roman Age, is also provided. The results indicate the existence of an ancient cultural landscape with a mosaic of open grasslands, natural forests and fields. It is concluded that the evidence presented in this paper supports the hypothesis of prehistoric, rather than a medieval origin of the species-rich grasslands in the Bílé Karpaty Mts.