Phylum: Charophyta   Family: Mesotaeniaceae

Mesotaenium macrococcum (F.T. Kützing) J. Roy & J.P. Bisset 1894

First described by Kützing (1845: 153) as Palmogloea macrococca. It was later moved to Mesotaenium by Roy & Bisset (1894: 253). Similar to M. chlamydosporum in size and habitats but the chloroplast in the former fills the cell in face-view.
Cell dimensions: L: 15-37 µm; B: 8-17 µm; L/B: 1.4-3.1.
Found in atmophytic habitats such as dripping rocks and on moss and other substrates, but also in abandoned peat-cuttings and moorland bogs and pools.

References: 
Brook, A.J. & Williamson, D.B. (2010) A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Kützing, F.T. (1845) Phycologia germanica, d. i. Deutschlands Algen in bündigen Beschreibungen. Nebst einer Anleitung zum Untersuchen und Bestimmen dieser Gewächse für Anfänger.
Roy, J. & Bisset, J.P. (1894) On Scottish Desmidieae.