Cosmarium obsoletum. Notice semicircular semicells, broad isthmus and hyaline thickening of the cell wall at the basal angles. Notice also pronounced cell wall pores. In the thickening of the left-hand basal angle of the lower semicell an extra large conical pore is to be observed.

Cell dimensions (L x B): ca 50 x 60 µm



Desmid of the month
January 2013

Cosmarium obsoletum

C. obsoletum is a smooth-walled, firm-lined Cosmarium species marked by a broad isthmus and semicells that are depressed semicircular in outline. Most characteristic is the cell wall at the basal angles, i.e., thickened and often perforated by a large conical pore. C. obsoletum has its main point of distribution in tropical regions. From the Netherlands only a few records are known (in oligo-mesotrophic moorland pools) dating from the first half of the last century.

Another cell of C. obsoletum (DIC image)

SEM picture of Cosmarium obsoletum