Phylum: Charophyta   Family: Desmidiaceae

Cosmarium homalodermum Nordstedt 1875

Semicells subtrapeziform, sinus slightly dilate at the apex, closed for the most part then opening widely. Basal angles broadly rounded, lateral sides straight or slightly convex, apex more or less truncate. All angles can show wall-thickening: when the apical angles are thickened it gives the inpression that the apex is retuse. Chloroplast axile with one large pyrenoid. This taxon is proving to be quite variable in size and also in the number of pyrenoids per semicell. Several populations have supported two, but most common is one pyrenoid. W. & G.S. West (1905: 182) reduced this taxon to a variety of Cosmarium hammeri without further comment. C. hammeri is proving to be ill-defined and more recent authors (Kouwets 1997, Mazalová et al. 2013) have reverted to C. homalodermum, as described by Nordstedt (1875: 18, pl. 6: 4). A widespread but rare desmid found in spring moorland pools and with moss on wet rocks.
Cell dimensions: L: 54-69 µm, B: 42-52 µm, Is: 15-21 µm; Th: 25-35 µm, L/B: 1.2-1.4.

References: 
Kouwets, F.A.C. (1997) Contributions to the Knowledge of the French Desmid Flora. I. New and Noteworthy Taxa from the Central and Eastern Pyrenees.
Nordstedt, C.F.O. (1878). De algis aquæ dulcis et de Characeis ex insulis Sandvicensibus a Sv. Bergren 1875 reportatis.
Mazalová, P., Štepánková, J. & Poulícková, A. (2013) Desmid flora of mires in Central and Northern Moravia (Czech Republic)