Phylum: Charophyta   Family: Closteriaceae

Closterium tumidulum  F. Gay 1884

Generally scarce but can be locally common in acidic and mildly alkaline conditions. Moorland lochs with peaty margins and ephemeral water bodies, usually in winter. Very similar to Closterium incurvum. but that species lacks the tumidity and has less crystals.

References: 
Brook, A.J. & Williamson, D.B. (2010) A Monograph on some British Desmids
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands