Phylum: Charophyta Family: Desmidiaceae
Cosmarium moniliforme Ralfs 1848
Possibly widespread in nutrient poor condition, but not proving common in the Outer Hebrides. This species and its two varieties have some overlap in terms of size and quotient ratio, so not always easy to determine
References:
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
West, W. & West, G.S. (1908) A Monograph of the British Desmidiaceae, Volume 3