Phylum: Charophyta Family: Desmidiacea
Cosmarium venustum var. excavatum (B.Eichler & Gutwinski) West & G.S. West
Of common occurrence in acidic pools and bogs. The distinguishing characteristic is the large scrobicula approximating to the centre of the semicell (see more details on the images). There is some doubt as to whether this variety is justified as most cells seem to have the scrobiculae. Where they are supposedly missing might be camouflages by the chloroplasts or naturally faint or missing in some cells. There is a large size-range within this species with cells from the Outer Hebrides currently L x B: 23.6–45.8 x 18.6–33.7 µm.
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles
Tsarenko, P.M., Wasser, S.P. & Nevo, E. editors (2014) Algae of Ukraine, Volume 4: Charophyta