Phylum: Charophyta   Family: Desmidiaceae

Cosmarium furcatospermum  West & G.S. West 1894

West & West (1908: 206) likened it to C. sphalerostichum Nordstedt 1876 noting in particular the difference in the zygospores. However, there is some doubt as to the reliability of the spore depicted. By 1908, the Wests had slightly altered their 1894 original diagnosis regarding cell-size, presumably based on additional data from Ireland. The Outer Hebridean finds are in close agreement with the 1908 data, but later authors have stretched these parameters to include possibly different taxa.
Cell dimensions: L: 17.8-21 µm; B: 15.3-19 µm; Is: 5.3-6.1 µm; Th: 10.2-11.5 µm; L/B: 1.11-1.18.
Infrequently recorded, probably confined to Atlantic regions. Found in oligo-mesotrophic waters that are slightly acidic to slightly alkaline such as loch-margins and abandoned peat-cuttings.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
West W. & West, G.S. (1908). A Monograph of the British Desmidiaceae, Volume 3.