More very rare desmids

September 30th 2020

More very rare desmids

Recent collections of desmids in Assynt have included some more very rare forms, identified and drawn by David Williamson.  Two examples are illustrated here, from samples collected on a visit to the vicinity of Loch Uidh nan Corp in Brackloch on 26thMay 2020 (see article posted on  27th June).

1st drawing

The banana-shaped Closterium nematodes var. proboscideum (photo 1) was in a sample from an unnamed lochan south of Loch Uidh nan Corp (NC116246). The loch is surrounded by beds of great fen-sedge Cladium mariscus (photos 2-3).  David described the desmid flora of this lochan as ‘outstanding’ and listed, in all, 17 species from the sample (see also below, under P.S.).

Only two previous records of this variety are noted in a monograph on British desmids (Brook and Williamson, 2010).  It was found new to the British Isles, ‘in squeezings of Utricularia sp. taken [by IME, on 8th July 1994] from a small unnamed lochan at the western end of Cam Loch, Assynt’ (NC186146), and subsequently in a sample from ‘the margins of  Loch Chealamy, Strathnaver’, West Sutherland (NC7250).

2nd drawing

The dumbbell-shaped Cosmarium zonatum var. angustum (photo 4) was one of 18 species found by David in a further sample, from the southern shore of An Ruadh Loch (photo 5, NC118250).   The species was first described from near Rhiconich, West Sutherland, in 1908, but this variety is not listed in David’s account of the Assynt desmid flora (Williamson, 1996) and there are no records for the British Isles on NBN.

P.S.  Since this article was first drafted, David has been having a further look at the desmid sample from the unnamed ‘Cladium loch’ at NC116246.  In an enthusiastic letter of 9th July, he informed us that this ‘turned out to be one of the best samples I’ve had for some years’, with an additional 39 taxa, making 56 in all.  This betters the two richest sites described in his 1996 paper, which were a lochan near Braclaich, at the north-western end of Cam Loch (NC186146), and Lochan Feoir on Quinag (NC227250), each of which mustered 55 taxa.  For the record, David is one of few algologists worldwide specializing in this group, still working actively in his early nineties.  We continue to send him samples from Assynt, and further afield in West Sutherland, and he replies with a full list from each locality and free-hand pencil drawings of any of special interest.  The lists and drawings are being archived as a unique record of this aspect of the local freshwater life.

References

Brook, A.J and Williamson, D.B, 2010.  A Monograph on some British Desmids.  London: Ray Society.

Williamson, D.B., 1996.  A Survey of the Desmid Flora of Assynt, West Sutherland.  Bot.J.Scotl. 48(2), 235-279.

 

Ian M. Evans and Gwen Richards

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