Phylum: Charophyta   Family: Desmidiaceae

Xanthidium laeve (W. Schmidle) P.F.M. Coesel & K.J. Meesters 2023

The main feature of this taxon is the wide-open sinus and rounded basal angles and the lack of anything approximating to a central protuberance. The spines are relatively stout and are positioned at the lateral and apical angles.
Single cell dimensions: L: 79 µm; B: 63 µm; Is: 22 µm; Sp: 15-16 µm; Overall LxB: 97-94 x 70-105 µm.
West & West (1912: 68) record it from the Isle of Lewis but it would seem to be quite rare. Found in variously acidic waters such as loch-margins and moorland pools, also with Sphagnum.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.