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Plectonema

Generic name: PLECTONEMA Thuret ex Gomont, 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 96.
Synonyms: [PLECTONEMA Thuret, Essai de classification des Nostochinees, in Ann.des Sc. nat., 6e serie, Bot., I, p.375 et 379, 1875 ex Gomont, 1892: Calothrix, Scytonema, Lyngbya, Plectonema, Hypheothrix spec.
Diagnosis: Gomont (1892): Fila vaginata, libera, eruptione laterali trichomatis pseudo-ramosa, pseudo-ramis solitariis aut geminatis. Vaginae firmae, hyalinae, rarius luteo-aureae. Trichomata frequenter ad genicula constricta; apex trichomatis rectus, rarissime attenuatus; calyptra nulla.
Plantae Scytonematis facie, saepius caespitosae et hydrophilae.
Type species: Plectonema tomasinianum Gomont ex Gomont 1892. - From many described species about 8 valid (originally heterogeneous genus ).
Descriptions:
Komárek (1992): Filamentous; filaments long, isopolar, solitary or in macroscopic clusters, usually waved or coiled, always with more or less thick, firm, colourless sheaths, sometimes slightly lamellated, open at the apex, obligatory and frequently falsely branched. Trichomes isopo1ar, 8-25 μm wide, uniserial, composed of shortly cylindrical or barrel-like (discoid) cells (always shorter than wide, usually several times), constricted or unconstricted at the cross walls, not attenuated or very shortly attenuated towards the ends, immotile (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.
Genotype differences, molecular data:
Reproduction strategies, life cycles, cell division:
Komárek (1992): Cell division crosswise, perpendicularly to the long axis of a trichome, in a rapid sequence. Irregular meristematic zones. Reproduction by motile hormogonia, liberating and escaping from sheaths at the ends of filaments, by means of necridic cells. Hormogonia germinate end grow at both ends (isopolar development). The absence of heterocytes was hesitated by Hoffmann et Demoulin (1985); in the case of heterocyte production must be Plectonema transferred into Scytonema (Nostocales).
Ultrastructure:
Taxonomic position, higher hierarchy: Cyanophyceae,
Oscillatoriales, Oscillatoriaceae, Plectonematoideae
Notes to taxonomy, misinterpretations:
Ecology, ecophysiology, ecological significance:
Komárek (1992): In clear (usually katharobic to oligosaprobic) water basins, springs or creeks, in metaphyton and periphyton.
Physiology and biochemistry:
Distribution, endemism, problematic citations:
Reference strain:
Infrageneric scheme, species concept:

List of species:
Plecotnema capitatum Lemmermann 1907
Plectonema litorale Anand 1937
Plectonema radiosum Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 100
Plectonema tomasinianum Bornet ex Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 99
Plectonema wollei Farlow ex Gomont, 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 98

Unclear taxa:
Plectonema araucanum Schwabe 1960
Plectonema rhenanum Schmidle 1901
Plectonema volkensii Schmidle 1901
Plectonema wollei f. gracilis Frémy 1930
Plectonema wollei f. robustissima Frémy 1930

Excludenda:
Plectonema nostocorum Bornet ex Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 102(= Leptolyngbya)
Plectonema purpureum Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 101(= Pseudophormidium)
Plectonema roseolum Thuret ex Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 102 (= Leptolyngbya)
Plectonema tenue Thuret ex Gomont 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 101 (= Pseudophormidium)
Plectonema terebrans Bornet et Flahault ex Gomont, 1892. Ann. Sci. Nat. Bot., ser. 7, 16: 103 (= Leptolyngbya)

Keys:
List of stains:
Drawings:
Komárek 1992
Application technology:
Literature:
  2.1 taxonomy: Geitler 1932, Anagnostidis & Komárek 1988, Komárek 1992
  2.2 cytomorphology:
  2.3 16S rRNA sequencing:
  2.4 biology and life cycles:
  2.5 ecology: