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Cyanobacteria (Cyanophyta)
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- By B.A. Whitton
- David M. John, Brian A. Whitton, Alan J. Brook
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- Book:
- The Freshwater Algal Flora of the British Isles
- Published online:
- 12 January 2024
- Print publication:
- 05 August 2021, pp 31-158
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Summary
Introduction
The blue-green algae (Cyanobacteria) are unicellular or filamentous organisms that sometimes form structures recognizable with the naked eye, but usually require a microscope for identification. They differ from all other groups in this Flora in that they are prokaryotes: their cell contents are not differentiated into membrane-bound structures such as the nucleus, chloroplasts and mitochondria. The popular name for the group, blue-green algae, comes from the colour of the cells seen under the microscope. The photosynthetic pigments in the membranes inside the cells contain chlorophyll a, which gives a green colour, but almost all species can form the blue pigment, phycocyanin, under some conditions and some also forma red pigment, phycoerythrin. The cells therefore often appear blue-green, but sometimes shades of purple, when all three pigments are present. Visually obvious growths are also often blue-green, but sometimes they are brownish, purple or orange. This is because many species have a sheath around individual cells or the whole filament and this sheath is often golden or dark brown, or sometimes a shade of red.
Many blue-green algae are easy for someone without specialist knowledge to recognize under the microscope to the genus or even the species. However, the group has gained a reputation for being difficult to identify reliably. This is partly because some species are morphologically highly variable and in some cases groups of species which appear distinct in one place all tend to merge with each other elsewhere. However, there are also problems due to the different approaches which have been used to name the organisms. The most important difference is between the botanical and bacteriological approaches. The bluegreens are anomalous in that they have been treated by some authors under the conventions of the International Code of Botanical Nomenclature, while others under the International Code of Bacteriological Nomenclature.
The present account includes marine as well as freshwater and terrestrial species. Some species occur in both types of environment: many freshwater species extend into brackish environments and a few marine species also extend into brackish environments. Morphologically similar forms occurring in non-marine and marine environments have sometimes been given different names and in other cases the same name. At least with the current state of knowledge for the British Isles, there are relatively few strictly marine blue-green algae, so it seems best to provide an account of the whole Flora.
Phylum Glaucophyta
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- By B.A. Whitton
- David M. John, Brian A. Whitton, Alan J. Brook
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- Book:
- The Freshwater Algal Flora of the British Isles
- Published online:
- 12 January 2024
- Print publication:
- 05 August 2021, pp 766-767
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- Chapter
- Export citation
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Summary
This phylum was established to accommodate those algae with intracellular blue-green coloured cyanelles rather than chloroplasts, but where the main part of the cell cannot be assigned easily to another phylum such as the diatoms. Cyanelles are evolutionary steps between blue-green algae and chloroplasts, though are more like the latter than the former; they cannot exist independently of the host cell. The cyanelles of some genera have been treated as separate species, with their own Latin name, but as they cannot exist independently of the host cell, this is a doubtful practice. There is no reason to believe that the various types of host cell are closely related to each other. The phylum is therefore probably artificial. Ideally, organisms with cyanelles should be placed in the phylum which the host cell most closely resembles. However, the phylogenetic relationships of the genera Cyanophora, Glaucocystis and Gloeochaete are still unclear, so the phylum is retained for the time being. However, ribosomal RNA sequences indicate that the cyanelles of these three organisms do show considerable similarity (Helmchen et al., 1995). These authors also showed that the cyanelles of another cyanelle-containing organism, Glaucosphaera vacuolata (not recorded from British Isles), indicate that this belongs to the Rhodophyta.
Gloeochaete was included in the green algal order Tetrasporales in the 2002 Flora and 2003 Coded List and its coded number is retained here in the hope that the taxonomic relationships of these organisms will soon be resolved, so it seems unnecessary to make the change now. It is listed in the Glaucophyta here, as was suggested originally by Kies (1976).
1 Cells motile with 2 unequal flagella emerging from a subapical depression…………….Cyanophora
1 Cells non-motile……………………………………………. 2
2 Cells ellipsoid; cyanelles twisted around each other and typically 8 towards each end; reproduce by autospores ………………………………..Glaucocystis
2 Cells spherical; cyanelles usually ovoid or sausageshaped and lying in a cup-shaped region; reproduce by biflagellate zoospores ………………..Gloeochaete
Cyanophora Korshikov 1924
05050000
Cells flattened, ellipsoid, possessing 2 unequal flagella emerging from a subapical depression. One to 2 (when mature) cyanelles per cell. Reproduction by longitudinal division into 2 daughter cells each with a cyanelle.
Three known species.
Cyanophora paradoxa Korshikov 1924
05050010 Pl. 71H (p. 278)
Cells 2–3 μm thick, 5–8 μm wide, 8–12 μm long; 1–2 blue cyanelles.
Plankton of shallow lakes with hard, nutrient-rich water.