Phylum: Charophyta   Family: Desmidiaceae

Cosmarium notabile Brébisson 1856

Brébisson’s (1856: 129, pl. I: fig. 15) original description and accompanying figure are poor, which has led to possible misidentifications. It has much in common with the also confused Cosmarium crenatum Ralfs (1848: p. 96, pl. 15: 7a-c). Van Geest & Coesel (2019: p.123, figs. 3, 12-14, 21.) found cells in ephemeral rainwater puddles near Amsterdam, which they feel fits Brébisson’s original concept. They also noted a degree of morphological variability within the sample. They present an SEM micrograph showing a faint supraisthmial row of poorly developed warts, which are easily overlooked. Kouwets (in manuscript) has scrutinised the literature and tried to bring some order to these crenate taxa. The Stornoway Quarry sample was quite rich in this taxon. With the exception of one cell (L: 30.1) the sizes compare favourably with the Amsterdam series and are remarkably consistent. The supraisthmial warts are a little easier to see in some cells but not in others (another variable feature). In view of the foregoing, distribution is largely unknown. It does seem to be a rare desmid confined to ephemeral pools and mosses on wet rocks.

References: 
Brébisson, L. A. de (1856) Liste des Desmidiées, observées en Basse-Normandie.
Van Geest, A. & Coesel, P. (2019) Some new and interesting desmids (Streptophyta, Desmidiales) from ephemeral puddles in the urban and industrial areas of Amsterdam (Netherlands).
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.