SOME NOTES ON THE DESMID GENUS GENICULARIA
Coniferae, Walnut Tree Lane, Loose, Maidstone, Kent. ME15 9RG.
Genicularia are tubular cells without a median constriction, the cell wall is covered with minute granules, ( W.&.G.S. West (1904) (1) figure G.spirotaenia from Loch Beosetter in the Shetland Islands, Scotland, with minute spines Fig.1). They were originally classed with the Saccoderm desmids but now together with Gonatozygon they have been transferred to the Placodermae, minute pores having been found in the walls of the related genus Gonatozygon, Genicularia are assumed to have the same wall structure.
" The genus Genicularia is one of the rarest of all known genera of Desmids" W.& G.S.West (1904) (2). The author has found the genus in samples from two sites on the Isle of Skye, Glen Drynock, and Loch More-na Caiplaick, Scotland collected by Mr Alan Joyce, who states the genus is variable and not uncommon in the Rhiconich area of Sutherland, Scotland.
The size range given by W.&.G.S.West (2) is :- G.spirotaenia De Bary 1858 cells 20-25 µm broad, 200-400 µm long. Length - Breadth 10-20 µm. G.elegans W.& G.S.West (1903), is a more slender sp. 14-16.3 µm broad, 303- 427 µm long. Length -Breadth 21-30 µm. The size range in the sample from Skye is :- 16-18.5 µm broad, 222.5-300 µm long, Length - Breadth 14-18.5 µm slightly narrower than the sizes given for G.spirotaenia above, most of the cells were of greater breadth than that given for G.elegans, 12 cells were measured 2 filaments of 3 cells and 6 individual cells.
Figure 1. Complete cell and enlargement to show spines
There are two parietal spiral chloroplast in each cell from the Isle of Skye with 2 to 6 'turns' in each cell. Some showing lax turns and others tighter with more turns, photo' shows part of cell. W.& G.S.West(2) figure G.elegans with laxer spirals than G.spirotaenia Fig.2. Contradicted by Prescott et al (1972) in their text, G.spirotaenia:- 'more lax turns than G.elegans.'
Figure 2. Complete cell
Filaments of 3 cells joined, and individual cells, some geniculate (they bend like a knee joint to conjugate), distinguished from the related filamentous algae Spirogyra by the slightly enlarged apices of each cell, the small granules which make the cell walls appear rough and the fact that the cells readily disassociate when attempts are made to manipulate them. Although there is no median constriction of the cell wall, or median division of the chloroplast; that is, they are not obviously semi-cells; as in most of the placoderm desmids, it could be seen in some individual cells that there are two semi-cells as one is distinctly more mature than the other, the granules being slightly larger and clearly seen, the younger semi-cell appearing smooth by comparison. The cells with 6 turns of the 2 intertwined chloroplast had 3 turns in each semi-cell joined by a short straight section about the median area, thus the chloroplast although continuous was clearly divided between the two semi-cells. Indian ink added to the water showed up a mucilage envelope, this mucilage appeared thin and absorbed some of the ink, showing as a lighter grey rather than white like the desmids with a copious mucilage.
During later observations one was cell found 344.5 µm x 11 µm only vestiges of chloroplast could be seen, size suggest G.elegans. Other specimens were seen with a slight swelling of the cell walls as though new apices were forming in the median area and the chloroplast was also dividing at this point. Many desmids will live and reproduce for months, even years, if kept in a cool place in North light, but the Genicularia chloroplast deteriorated within a few days.
Williamson (1992) in a comprehensive survey of the desmids of the Shetland Isles, collected from Loch Beosetter, (where the West's recorded G.spirotaenia) no Genicularia were recorded.
Although there is some variability in the laxity or otherwise of the chloroplast spirals and the breadth of most cells were larger than those recorded by W.&.G.S.West for the species, the specimens from Skye were considered to be G.elegans.
There are filaments of Gonatozygon aculeatum Ruzicka in the samples, typically 203 x 8 µm, single spiral chloroplast, short spines on cell walls.
Figure 3a and 3b. Photomicrographs, arrow points to where cells join.
The author is grateful to Mr. Alan Joyce for the samples and his helpful comments. To Dr. J.W. Lund curator of The Fritsch Collection of Alga Illustrations at The Freshwater Biological Association, and to Mr. David Williamson for a copy of his paper on the desmids from the Shetland Isles. References:-
Lind E.M. Brook A.J. 1980. Desmids of the English Lake District, Freshwater Biological Association, Scientific Publication No.42.
Prescott G.W., Croasdale Hannah T.,& Vinyard W.C. 1972. North American Flora. Series II. Part 6.
West W.&.G.S. 1904 (1). Freshwater Algae from the Orkneys & Shetlands. From The Transactions & Proceedings of the Botanical Society of Edinburgh. Ed. D.J.Scourfield.
West W.&.G.S. 1904 (2). A Monograph of the British Desmidiaceae. Vol.1. Ray Society.
Williamson D.B. 1992, A Contribution to our Knowledge of the Desmid Flora of the Shetland Islands, The Botanical Journal of Scotland.
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