THE DESMIDS of THURSLEY
by William Ells
Coniferae, Walnut Tree Lane, Loose, Maidstone, Kent. ME15 9RG. UK.
Thursley Common, Surrey, England is a Site of Special Scientific Interest (SSSI) . Comprising 326 hectares owned by English Nature. The bog is of great interest to microscopists both amateur and professional, and in particular to desmid enthusiasts like myself.
David Bellamy, Britain's best known botanist, has stated that Thursley Common is his favourite SSSI. A place where black bog rush and scorpion moss vie with sheets of desmids and other algae for their place in the sun.
My own interest in desmids started in 1979 and after reading in a paper by G.A. Early in 'Microscopy' In Praise of Desmids (with observations on the desmid flora of Thursley Common) in 1981, that this was the first paper to be published in 'Microscopy' on these important unicellular freshwater plants since 1961. I decided to try and specialise.
After spending some time examining the local ponds and the only acid bog in Kent at Hothfield and found altogether only about 25 species, although in one small pond record numbers of a single species - Staurastrum tetracerum (Kütz.) Ralfs 1845. I decided it was time to visit the source of Mr. Early's impressive list. I found Thursley bog to be a typical acid bog with bog cotton and two of the three British species of the insectivorous plant the Sundew Drosera rotundifolia & D. intermedia good indicators of acid conditions.
I did not find sheets of desmids, however I did find the rare Roya obtusa (Bréb) W.&.G.S.West 1896. Fig 1. and the not very common Micrasterias oscitans Ralfs 1848 Fig 2. Mr. Early in a letter in July 1988 informed me his list of species/varieties now numbered 110 but did not include R. obtusa or M. oscitans. Neither did it include Staurastrum muricatum (Bréb) Ralfs 1848. or Pleurotaenium minutum (Ralfs) Delp. 1877 var. minutum. We discovered his list included the latter desmid as Penium minutum. W.&.G. S. West confusing matters. In fact this desmid has been in seven different genera, it was proposed in a paper by Bando (1988) to transfer the Pleurotaenium minutum group to a new genera Haplotaenium I do not know if this has been universally adopted.
On the 10th. of July 1992 after a prolonged spell of dry weather there was very little water in the boggy area, I collected from two of the wettest places where bog cotton was growing and also from some of the pools beside the bridle path which were also very low. In the first of these pools I found Closterium acutum (Bréb) Ralfs, conjugating and zygospores forming, a rare occurrence Figs 3 & 4.
In the third pool I found the not very common Spirotaenia condensata (Bréb) Ralfs 1848. Fig 5. Although I have now made several visits and a friend has also given me a sample, I have not found as many species/varieties as Mr. Early.
Not a desmid , but I could not resist putting in a microgaph taken with flash of a live rotifer I have not seen elsewhere, Fig.6. Trichotria tetractis from a sample collected at Thursley in 1988.
There are no restrictions on entry to the site, however you should get a permit to collect samples from Thursley from English Nature, The Countryside Management Centre, Coldharbour Farm, Wye, Ashford, Kent. TN25 5DB. Collect about 100 ml. from several points rather than a litre from any one place. If you decant each sample from one tube to another through a tea strainer you will avoid taking away macro fauna such as water beetles. If you have with you a suitable flat container, a small photo' developing dish is ideal, you can examine any beetles, water mites, etc. before returning them to the bog. TAKE ONLY WHAT YOU REALLY NEED.
Acknowledgements:- Many thanks to Mr. Eric Hollowday for identifying the rotifer. To Alan Brook Emeritus Professor of Life Sciences at The University of Buckingham, for a copy of the paper by Bando. And to the Editors of 'Micscape' for scanning my photomicrographs for publication.
Bando 1988. Haplotaenium (nov.com) Journal of Japanese Botany, Vol. 63. No. 5.
Early. G.A. 1981 In Praise of Desmids (with observations on the desmid flora of Thursley Common) Microscopy, Journal of the QMC. Jan-June 1981 Vol.34. Part 3. pp 207-213.
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