Desmid of the month
February 2015

Closterium acutum

Closterium acutum is marked by delicate, about needle-like cells that gradually attenuate from their mid region to the narrowly rounded apices (in low magnification seemingly acute). Shape of the cells may vary from almost straight to semicircular.  Often, curvature is not uniform but (partly) sigmoid to a lesser or higher degree. Cells of Cl. acutum that are strongly curved and/or highly sigmoid are accounted var. variabile.  Zygospores are quadrangular with 4 horn-like processes. Cl. acutum has a wide ecological range varying from oligotrophic bog pools to eutrophic ponds. In particular var. variabile may be very abundant in eutrophic water bodies. In the Netherlands, Cl. acutum is a common species. Zygospores are only incidentally encountered.