Distributions of vascular plants in the Czech Republic. Part 4.
This the fourth part of the series on the distributions of vascular plants in the Czech Republic includes grid maps of 84 taxa of the genera Aldrovanda, Alisma, Asclepias, Azolla, Blechnum, Botrychium, Butomus, Carex, Centaurea, Drosera, Dysphania, Hypochaeris, Illecebrum, Luronium, Ophioglossum, Persicaria, Pilularia, Rubrivena, Sagittaria, Salvinia, Scirpoides, Sideritis, Streptopus, Teesdalia and Thesium. These maps were produced by taxonomic experts based on herbarium specimens, literature and field records. Of the native taxa studied, 40 are on the national Red List. Among them, Carex pseudobrizoides, Hypochaeris glabra and Illecebrum verticillatum are rare species of mainly sandy habitats, which are all now restricted to a few or several sites and are therefore classified as critically threatened. Endangered aquatics and wetland plants are represented by Alisma gramineum, Salvinia natans, three Drosera species, Luronium natans and Pilularia globulifera, of which the latter two are species with sub-Atlantic distributions, reaching in this country their south-eastern and eastern distribution limits, respectively. All eight species of the genus Thesium and most species of Botrychium are endangered, either because they are rare or they are now considerably less common than they were, or combination of both. Two of the species mapped in this paper are now extirpated from this country. Botrychium simplex was last recorded more than 120 years ago, whereas the spontaneous occurrences of Aldrovanda vesiculosa vanished after 1952. However, the latter species has recently been deliberately planted in the wild for conservation purposes. The taxonomically extremely difficult Centaurea sect. Jacea, whose taxonomy and evolution is complicated by polyploidization and frequent hybridization, includes many taxa whose distributions were unclear until recently. Maps of Centaurea species and subspecies based on revised herbarium specimens are given, supplemented with the occurrence of their hybrids in grid cells where the parental species have not been documented. Alien species are mainly species originally introduced into Europe as ornamental and/or medicinal plants, such as Azolla filiculoides, Carex muskingumensis, Rubrivena polystachya, Sagittaria latifolia, three species of Dysphania and two of Persicaria. Another one, Asclepias syriaca, has become locally abundant and invasive. Other aliens were introduced unintentionally, such as Dysphania melanocarpa and D. pumilio with wool from Australia or Persicaria pensylvanica with soybeans from North America. Spatial distributions and temporal dynamics of individual taxa are shown in maps and documented by records included in the Pladias database and available in electronic appendices. The maps are accompanied by comments, which include additional information on the distribution, habitats, taxonomy and biology of the taxa.