Phylum: Charophyta   Family: Desmidiaceae

Cosmarium pseudopyramidatum var. extensum  (Nordstedt) Willi Krieger & Gerloff

This variety has the general outline of a pyramidatum but is more elongate, resulting in a higher L/B ratio: 1.75-2.00. Rarely recorded but possibly confused with similar species.

References: 
Krieger, W. & Gerloff, J. (1962-9) Die Gattung Cosmarium
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium