This species-poor type of marsh vegetation is dominated by dense stands of the tall sedge Cladium mariscus, which is typical of calcareous fens in an advanced stage of terrestrialization. It occurs in water up to 100 cm deep, but can also be found in places where water is below the soil surface for most of the growing season. Natural habitats include puddles and the surroundings of springs in lowland fen complexes, however, it also occurs in man-made habitats such as wet pits in calcareous bedrock. This is a relict vegetation type, which used to be more common in lowland fens in the early Holocene, but has retreated due to loam sedimentation and the draining and conversion of fens into arable land. Currently it is found at four sites in the middle Labe area between Mělník and Lysá nad Labem.