Detailed research into desmids in Dutch rich fen areas in the past decades has shown that peat excavation ditches and fen hollows accommodate a high diversity of species. This has also stimulated taxonomic research on individual species from these environments. This article discusses the taxonomy of Cosmarium pachydermum; a form frequently associated with this species as var. aethiopicum is described as a new species C. coeselii, named after Peter Coesel in honor of his great significance for desmid research in the Netherlands. Cosmarium coeselii can be distinguished from the nominate variety of C. pachydermum by its more regularly curved semicell outline, somewhat smaller size and narrower isthmus. Cosmarium coeselii is a widespread but never common species of quaking bogs and mesotrophic lakes with some supply of minerals and is known to date from the Netherlands and France. Cosmarium pachydermum has a similar ecological preference, but is only rarely found in fen areas in the Netherlands. In the rest of Europe, this species seems to prefer upland and mountainous areas.

, , , , , , ,
Gorteria Dutch Botanical Archives

CC BY 3.0 NL ("Naamsvermelding")

Naturalis Biodiversity Center

F.A.C. Kouwets, M.C. van Westen, & B.F. van Tooren. (2021). Cosmarium coeselii: a characteristic new desmid species from Dutch broads areas. Gorteria Dutch Botanical Archives, 43(1), 103–108.