In the
samples of estate De Teut Belgium, taken on Saturday 23rd of June, I found some
interesting species of desmids. I wrote about Micrastrias fimbriata in my
previous hydrobiology blog. In the same sample of ‘the ditch’ I found Cosmarium
contractum var. contractum and Closterium closteroides var. closteroides,
though the last desmid might be named differently in the future or might be
split up in different taxa.
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| Cosmarium contractum var. contractum Olympus IX81 + DP72 960x immersion-oil EFI photograph. |
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| cf Closterium closteroides var. closteroides Olympus IX81 + DP72 200x immersion-oil. |
Cosmarium
contractum var. contractum is a small-sized desmid, that can easily be confused
with a series of other smooth-walled Cosmarium species. The elliptic or oval semi-cells
are connected with a very deep, widely open sinus. Cell dimensions: length
30-56 μm, breath 17-40 μm (Coesel & Meesters 2007).
One of
the other species found in this sample was a bit confusing. The observation led
to Closterium closteroides var. closteroides, though the transversal
constrictions of the chloroplasts were only vaguely present. A distinct,
spherical vacuole can be recognized near the apex (top) and 3-6 pyrenoids per
chloroplast. Cell dimensions: length 280-310 μm, breath 40-45 μm.
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| The transversal constrictions of the chloroplast are only vaguely present. Olympus IX81 + DP 72 600x immersion-oil. |
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| The spherical vacuole near the apex. Olympus IX8 + DP72 600x immersion-oil. |
Marien
van Westen of Desmids of Drenthe commented that examples found in literature and websites mainly
pictured ‘ideal’ samples of the species, in which characteristics can be easily
seen. In reality this is not always the case.
Expert Ton
Joosten agreed that the variations in cell dimensions and constrictions can be
confusing: variations of the type are found and possibly wrongly labeled. The
variations of the type might even led to six different taxa based on cell
dimensions alone! For example, Closterium closteroides var. closteroides can be
confused with the smaller-sized Closterium navicula or Closterium libellula (sometimes
used as a synonym of Closterium closteroides var. closteroides) and not every
description is accurate or correct.
The information is mainly lacking
observations of zygospores and molecular inspection. Interpretation of
observations might be inaccurate as well. Decisions have to be made to get more
conclusive descriptions to keep the taxa apart. So for now I can only label my
observation as a carefully named Closterium closteroides var. closteroides sensu
J.Heimans in P.F.M. Coesel 1983.
Literature
Coesel PFM & Meesters KJ (2007) Desmids of the Lowlands - Mesotaeniaceae and Desmidiaceae of the European Lowlands, KNNV Publishing Zeist.
