Phylum: Charophyta   Family: Desmidiaceae

Cosmarium orthostichum  P. Lundell 1871

A widespread but rare species largely known from north-western Europe. Recent finds in the Outer Hebrides are from slightly acidic waters. They are slightly smaller than the accepted dimensions for this species so may represent a different, related, taxon.

References: 
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland.
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.