Desmid of the month
June 2004

Cosmocladium saxonicum

The colonial desmid genus Cosmocladium is characterized by small, smooth-walled, Cosmarium-like cells connected to a 3-dimensional colony by intercellular strands (see also C. constrictum). The strands consist of bundles of microfibrils that are secreted from  large cell wall pores located at the basis of the semicell on either side of the isthmus (Gerrath 1970). At cell division both of the older semicells produce new strands. Where, between both daughter cells, the ends of the strands contact each other a local inflation is observed.

Cosmocladium species are but rather rarely recorded. There are indications that in fixed material the characteristic interconnecting strands are lost so that individual cells may easily be confused with those of a smooth-walled Cosmarium species.

The best-known Cosmocladium species is C. saxonicum. In The Netherlands this species was encountered by Heimans in various mesotrophic water bodies in the first half of the last century; later records are wanting (*). The herewith reproduced colonies originate from a shallow pool in the Blue Mountains, New South Wales, Australia.

Reference:

Gerrath, J.F., 1970. Ultrastructure of the connecting strands in Cosmocladium saxonicum De Bary (Desmidiaceae) and a discussion of the taxonomy of the genus. — Phycologia 9: 209-215.

(*) see news October 2004