Phylum: Charophyta   Family: Desmidiaceae

Xanthidium scrobiculatum (Scott & Grönblad) Stastny, Skaloud & Neustupa 2013

First described and illustrated by Scott & Grönblad (1957: 30, pl. 17: 3-6) as Xanthidium cristatum var. scrobiculatum. It was later raised to species level by Stastny, Skaloud & Neustupa (2013: 415). An angular Xanthidium with 6 spines per semicell in face view. The median and apical ones are twinned, the basal ones are single. The centre of the semicells is coloured orange and has a circle of scrobiculae, sometimes barely visible.
Cell dimensions: L: 58-62 µm; B: 42-44 µm; Is: 16-18 µm; Sp: 11-12 µm; overall LxB: 79 x 64.
A very rare desmid found predominantly in North America including the southern part of Canada. There is just one record for the Outer Hebrides, which was found in the benthic layer of a very shallow and turbid loch.

References: 
Prescott, W.G. et al. (2001 reprint). A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 4.
Scott, A.M. & Grönblad, R. (1957). New and interesting desmids from the southeastern United States.
Stastny, J., Skaloud, P., Langenbach, D., Nemjova, K. & Neustupa, J. (2013). Polyphasic evaluation of Xanthidium antilopaeum and Xanthidium cristatum (Zygnematophyceae, Streptophyta) species complex.