Phylum: Charophyta   Family: Desmidiaceae

Haplotaenium minutum var. crassum (W. West) J. Cambra Sánchez 1998

It differs from the nominate variety in being shorter and broader resulting in a smaller L/B ratio.
Cell dimensions (2): L: 88-90 µm; B: 19.2-20.6 µm; L/B: 4.3-4.7.
West & West (1904) in their major flora, note: “Cells stout, sometimes a little inflated, 4-4½ times longer than their diameter, apices broad and truncate.” They give a few sites in Wales, Scotland and Ireland but it would seem to be a rare taxon. Found in mildly acidic moorland pools and bogs.

References: 
West, W. & West, G.S. (1904). A Monograph of the British Desmidiaceae, Volume 1.