Waarnemingen van kiemlingen, provegetatieve cellen en dichotypische cellen van enkele Cosmarium-soorten in het Zwanenwater

Observations of germlings, prevegetative cells and dichotypic cells of some Cosmarium species in the Zwanenwater (the Netherlands) An investigation of the desmid flora in dune pools and wet dune valleys of Zwanenwater (The Netherlands) revealed zygospores, germlings and prevegetative cells of Cosmarium corbula Brébisson and, most likely, also prevegetative cells of Cosmarium botrytis Ralfs. Observations of germlings and prevegetative cells in wild populations of desmids are rare. But the observations in Zwanenwater (Netherlands) give reason to assume that some stages are easily overlooked or interpreted as deformities or stages of the vegetative propagation of the species. While germlings are difficult to identify due to their undifferentiated appearance, provegetative cells can be easily distinguished from other reproductive stages. Observations of this type of cells, like the presence of zygospores, indicate a complete reproductive cycle of the species in a given habitat. Next to sexual stages of the above-mentioned species, a polymorphic population of Cosmarium commissurale Ralfs was encountered, some forms resembling Cosmarium trachypleuroides Van Westen & Coesel. The find of dichotypic cells combining semicells of those supposed taxa raises question after their taxonomic identity.