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Cosmarium corriense Desmid Species Outer Hebrides

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Phylum: Charophyta   Family: Desmidiaceae

Cosmarium corriense Bisset ex J. Roy 1894

A medium sized cell, about 1.4 times longer than broad, sinus open and parallel for half its length before opening widely, with a slightly oblique apex. Semicells are subrectangular with almost straight sides and broadly rounded upper angles with a convex apex. Cell-wall ornamented with a regular vertical series of small granules; the basal granules are doubled; apical view broadly oval, lateral view subcircular. Chloroplast axile with one pyrenoid.
A very rare desmid first found by J.P. Bisset in a quarry at Corrie, Isle of Arran, Scotland; see in Roy (1894, p. 44, pl. 2: 6). It was named after the site. Interestingly, the drawing shows a uniform series of single granules with no mention of the row nearest the isthmus being doubled. The measurements given: L. 43, B. 32, Is. 15 µm. suggest just a single cell was found. West & West (1908, p. 133, pl. 76: 1) refer to Bisset’s find and give a thickness of 21 µm (presumably measured from Bisset’s drawing). They also note another find in Kerry, Ireland. Kouwets (in manuscript) draws attention to Cosmarium ordinatum var. montanum Gutwinski (1909, p. 460, Pl. 7: 26), suggesting that it may be synonymous with the taxon under discussion.
Interestingly, the lower granules are drawn as doubled. Sizes given: L. 44, B. 35, Is. 17, Th. 22 µm.
Kouwets (l.c.) gives sizes as: L. 42-44 µm, Br. 31-35 µm, Th. 22-23 µm, I. 15-17 µm; L./Br. circa 1.26-1.37.
The Harris population is: L. 40.1-47.1 µm, B. 30.1-33.9 µm, Is. 14.5-16.2 µm, Th. 23.0-24.9 µm. L/B. 1.31-1.41.
The habitat would seem to be sub-atmophytic with moss on dripping rocks. It should be compared with the superficially similar Cosmarium porteanum W. Archer 1860. That species has rounded laterals, a more extended isthmus, no doubled granules and the size is smaller with little overlap.

Roy, J. (1894) On Scottish Desmidieae.
Gutwinski, R. (1909) Flora glónow Tatrzanskich. — Flora algarum montium Tatrensium.
West, W. & West, G.S. (1908) A Monograph of the British Desmidiaceae, Volume 3.
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.