Desmid of the month
April 2022

Closterium directum

Cl. directum is a medium-sized Closterium species with slightly curved to almost straight cells that but little attenuate from midregion to apex. It belongs to the group of species marked by a striate cell wall provided with so-called girdle bands. A relevant characteristic is made by the shape of the poles: often slightly recurved and ending in a broadly rounded apex. In the Netherlands, Cl. directum is of occasional occurrence in oligotrophic, acidic moorland pools.

Image © Alfred van Geest

Closterium directum. Notice slightly curved cell that but little attenuates towards the poles.

Cell dimensions (L x B): ca 300 x 20 µm

Image © Alfred van Geest

Closterium directum. Midregion of a cell showing longitudinal striation of the wall as well as a central girdle band left and right bounded by a transversal ring line.

Image © Alfred van Geest

Closterium directum. Detail of cell end showing a broadly rounded apex with a vacuole enclosing a single, compound crystal.