Recent find of Cosmocladium saxonicum in the Netherlands

A few months ago (June 2004) Cosmocladium saxonicum was presented on this website as ‘desmid of the month’. On that occasion a micrograph was used made by Michael Dingley, from Australia, as the species in question had not been found in the Netherlands for more than half a century. Most surprisingly, however, C. saxonicum was encountered some months after figuring on our site in a moorland pool near the Dutch village of Lochem.  As the algal material was still live when examined it lent itself to testing the hypothesis that the intercellular connection strands do not stand any fixation with formalin or alcohol. Indeed, adding of formalin (to a final concentration of 2 to 3 per cent) resulted in clumping of the cells within 24 h, the intercellular connection strands getting almost invisible.  A couple of days later the clumps of cells appeared to be disintegrated for the most part, resulting in scattered, separate cells. As those cells light-microscopically hardly or not can be distinguished from small-sized cells of Cosmarium contractum, in fixed samples Cosmocladium saxonicum will usually be overlooked.

Colony of Cosmocladium saxonicum from a Dutch moorland pool. The intercellular connection strands, with a characteristic median inflation, are most distinctive.

Micrograph of a Cosmocladium saxonicum colony, showing that the cells are not only kept together by intercellular strands but also by a common mucilaginous mass.