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Phylum: Charophyta   Family: Desmidiaceae

Cosmarium crenatum   Ralfs ex Ralfs

Found on wet rocks and shallow depressions in water with a pH either side of neutral. Described as an alpine and arctic desmid, the common British form has three crenations at each side of the semicell and four at the apex. There are variations though

Koos Meester

Coesel & Meesters (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
West & West (1904-23) A Monograph of the British Desmidiaceae
John, Whitton & Brook (2011) The Freshwater Algal Flora of the British Isles