Phylum: Charophyta   Family: Desmidiaceae

Cosmarium quadratulum (F.Gay) De Toni

One of many very small Cosmarium species which are difficult to define and lead to some confusion. An acidophile that is possibly rare but also under-recorded

References: 
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands