Plectonema Thuret ex Gomont, 1892

Lectotype species: Plectonema tomasinianum Bornet ex Gomont

Original publication and holotype designation: Gomont, M. (1892 '1893'). Monographie des Oscillariées (Nostocacées Homocystées). Deuxième partie. - Lyngbyées. Annales des Sciences Naturelles, Botanique, Série 7 16: 91-264, pls 1-7.

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Description: Filamentous; filaments long, isopolar, solitary or in macroscopic clusters, usually waved or coiled, always with more or less thick, firm, colorless sheaths, sometimes slightly lamellated, open at the apex, obligately and frequently false-branched. Trichomes isopolar, 8-25 _m wide, uniseriate, composed of short cylindrical or barrel-like (discoid) cells (always shorter than wide, usually several times), constricted or unconstricted at the crosswalls, not attenuated or very shortly attenuated towards the ends, nonmotile (with exception of hormogonia). Cells without aerotopes, sometimes with granular, blue-green, olive-green or grey-blue content; end cells widely rounded, sometimes capitate or with slightly thickened outer cell wall. Heterocytes and akinetes absent. Cell division crosswise, perpendicular to the long axis of a trichome, in a rapid sequence. Irregular meristematic zones. Reproduction by motile hormogonia, escaping from sheaths at the ends of filaments, by means of necridic cells. Hormogonia germinate and grow at both ends (isopolar development). The absence of heterocytes was doubted by Hoffmann and Demoulin (1985); in the case of heterocyte production Plectonema must be transferred to Scytonema (Nostocales). In clear (usually katharobic to oligosaprobic) water basins, springs or creeks, in metaphyton and periphyton.

Information contributed by: J. Komárek. The most recent alteration to this page was made on 2023-03-03 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as neuter.

Most recent taxonomic treatment adopted: Strunecký, O., Ivanova, A.P. & Mares, J. (2022 '2023'). An updated classification of cyanobacterial orders and families based on phylogenomic and polyphasic analysis (Review). Journal of Phycology 59(1): 12-51.

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 03 March 2023. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 16 April 2024

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