Scytonema C.Agardh ex É.Bornet & C.Flahault, 1886

Lectotype species: Scytonema hoffmannii C.Agardh ex Bornet & Flahault

Original publication and holotype designation: Bornet, É. & Flahault, C. (1886 '1887'). Revision des Nostocacées hétérocystées contenues dans les principaux herbiers de France (Troisième fragment). Annales des Sciences Naturelles, Botanique, Septième série 5: 51-129.

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Description: Filamentous - thallose; solitary branched filaments or mats on the substrate. Filaments free or in fascicles, sometimes densely coiled, creeping on the substrate or with erect branches, commonly falsely branched, with one or (obligatory) two lateral branches. Branching initiates after trichome dissociation by help of necridic cells between two heterocytes, usually not at heterocytes; both branches grow parallel aside or in crossing position; the filaments make sometimes typical loop-like lateral formations before branching, in which tops of the trichomes later divide. Trichomes isopolar, cylindrical, not diversified in basal and apical parts, uniseriate, usually with solitary heterocytes, constricted (rarely not constricted) at cross walls; terminal parts of branches cylindrical or slightly widened, with rounded apical cell; middle parts of trichomes sometimes with elongated, cylindrical cells. Sheaths firm, limited, parallel or diverging, lamellated, usually yellow-brown (colored by scytonemin) in some parts. Cells pale or olive-green, usually with solitary, irregularly disposed granules or with granular content, rarely yellowish or pinkish colored; apical cells sometimes with large vacuoles. Heterocytes intercalary, solitary, rarely in pairs, cylindrical or barrel-shaped. Akinetes were several times mentioned, but not proved and well described. Cells divide crosswise to the trichome axis, mainly in meristematic zones near the ends of branches. Reproduction by hormogonia, which develop at the ends of branches and liberate from sheaths. Hormogonia germinate at both ends and form isopolar filaments. Many Scytonema-species grow aerophytic or subaerophytic on wet rocks, wood, soil, epiphytic on mosses; several species are incrusted by calcium carbonate and represent dominant members of microphytes in travertine springs. Few species are known from atmophytic habitats near thermal waters. The submersed species grow usually in rocky littoral of lakes, rarely among water plants, mainly on alkaline substrate, rarely in moors or acidic waters, few species are marine, occurring on coral reefs or in brackish water. The genus is very common mainly in tropical regions, but particularly the variability of tropical taxa is insufficiently known and many species are arbitrarily misinterpreted.

Information contributed by: J. Komárek. The most recent alteration to this page was made on 2023-03-06 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. 06 March 2023. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 25 September 2023

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