Phylum: Charophyta   Family: Mesotaeniaceae

Mesotaenium minimum J.A. Cushman 1906

First described by Cushman (1906: 347). The smallest member of the genus found in Britain with an average breadth of 5 µm.
Cell dimensions: L: 11-22 µm; B: 3.2-6.8 µm; L/B: 2.0-5.5.
Found in mucilaginous masses atmophytically on moss and other substrates.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Cushman, J.A. (1906). New England desmids of the Subfamily Saccodermae.