Phylum: Charophyta   Family: Desmidiaceae

Cosmarium grantii  J. Roy & Bisset 1894

First described by Roy (1893, pl.1: 10) and Roy & Bisset (1894, p.102) from wet rocks in eastern Scotland. There have been no traceable records since until Van Westen & Coesel (2021, p.243, figs. 1, 9-11, 30) found cells in the Netherlands. These were in acidic habitats. There are similar species and the L/B ratio is a helpful indicator in separating them. The supraisthmial ornamentation depicted by Roy is two rows of fairly spherical granules. This feature is variable in all similar species and the row farthest from the isthmus is often seen as elongated warts (see Van Westen & Coesel’s fig. 11). The desmid was named in honour of Mr. P. Grant, a pioneer collector of desmidiaceae in the north-east of Scotland.

References: 
Roy, J. & Bisset, J.P. (1894). On Scottish Desmidieae.
Van Westen, M. & Coesel, P.F.M. (2021) Taxonomic notes on desmids from the Netherlands IV, with a description of another five new species.