Chlorodiscus natans Peter. and Hans. [Chlorophyceae] from a mesotrophic peat bog in Lower Silesia [South-Western Poland]

The paper concerns a very rare and poorly known species of green alga Chlorodiscus natans Petersen & Hansen, discovered in the peat bog "Brzeźnik" near Bolesławiec (Poland). This is the second stand so far discovered in the world. The collected material allowed complementing the knowledge on organization of colonies, morphology and way of hair development. The remaining features, particularly the structure of the cell, are in concordance with the hitherto diagnosis of that species. The paper presents problems connected with the taxonomic affiliation of the species and describes the ecological conditions of habitats occupied by this alga.