Phylum: Charophyta   Family: Desmidiacea

Xanthidium planum (Y.V. Roll) P.F.M. Coesel & K.J. Meesters 2023

A medium-sized cell with closed sinus for the most part. The lateral angles support stout spines that are decumbent. The apical angles support stout spines that lean away from the centre. Apices are truncate. The central protuberance in surrounded by small granules.
Cell dimensions: L: 55-69 µm; B: 49-63 µm; Is: 16-27 µm; Sp: 11-17 µm; Th: 41-42 µm; Overall LxB: 74-90 x 81-91 µm.
Found in acidic mesotrophic waters such as moorland pools and shallow lochans, but rarely recorded.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
John, D.M. & Williamson, D.B. (2009). A Practical Guide to the Desmids of the West of Ireland.
Van Westen, M.C. (2024). Sieralgen in Drenthe.