Phylum: Charophyta   Family: Peniaceae

Penium margaritaceum J. Ralfs 1848

First described and illustrated by Ralfs (1848: 149, pl. 25: 3 & 33: 1). Cells cylindrical with rounded apices, cell-wall with girdle bands and covered with small granules often in regular rows.
Cell dimensions: L: 90-200 µm; B: 15-30 µm; L/B: 6-10.
Although widely distributed it is thought to be rare and only infrequently recorded. Found in bogs and peaty pools plus loch-margins with vegetation.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848) The British Desmidieae.
Ruzicka, J. (1977) Die Desmidiaceen Mitteleuropas, Volume 1, Part 1.
West, W. & West, G.S. (1904) A Monograph of the British Desmidiaceae, Volume 1.