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
