Species of the genus Cymbella C.Agardh are widespread in European and Asian continental waters and form a significant portion of taxonomic diversity and the dominant complex of algal communities in phytopepiphyton of the Dnieper cascade of reservoirs and the Lower Dnieper. Representatives of this genus exhibit high morphological variability which is important for the taxonomy of Cymbella and Bacillariophyta in general. For that reason, investigations in this direction are topical at present. Samples of algae were collected from semi-aquatic plants (Phragmites australis (Cav.) Trin. ex Steud. – common reed) and submerged plants (Potamogeton pectinatus L. – fennel-leaved pondweed, Ceratophyllum demersum L. – morass-weed, Myriophyllum spicatum L. – meakin). Diatom frustules were released from organic matter by cold burning and then specimens were examined in a JSM-25S scanning electron microscope. This electron microscopy study investigates morphological variability of the frustules in populations of widespread species of the genus Cymbella (C. helvetica Kützing, С. neolanceolata W.Silva, C. proxima Reimer, C. subcistula Krammer, C. tumida (Brébebisson) Van Heurck) from phytopepiphyton in the Kiev, Kanev, Kremenchug, Dneprodzerzhinsk, Kakhovka reservoirs and the Lower Dnieper. Differences in some individual and groups of diagnostic quantitative characteristics (valve length and width, number of striae and areolae in 10 µm) have been found between our data and the published diagnoses which, in the author’s opinion, indicates interpopulation variability. Significant morphological variability has been shown in С. neolanceolata that gives reason to extend the species diagnosis. The results of our investigations into the variability of representatives of the genus Cymbella should be taken into account when conducting algological and hydrobiological studies as well as when using species of this genus for bioindication.
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