Phormidium Kützing ex Gomont, 1892
Lectotype species: Phormidium lucidum Kützing ex Gomont
Original publication: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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Type designated in Geitler, L. (1942). Schizophyceae. In: Die natürlichen Pflanzenfamilien,... Zweite Auflage. Band 1b. Schizophyta Klasse Schizophyceae. (Engler, A. & Prantl, K. Eds), pp. 1-232. Leipzig: Wilhelm Engelmann. Download PDF
Taxonomic status: currently recognized as a distinct genus.
Gender: This genus name is currently treated as neuter.
Most recent taxonomic treatment adopted: Strunecký, O., Ivanova, A.P. & Mareš, 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.
Taxonomic notes
Thomazeau et al. (2010: 575) note that Phormidium belongs taxonomically to the most difficult cyanobacterial genus and that the type species P. lucidum is subject to controversy (Komárek & Anagnostidis 2005). See also INA and ING. - (15 Feb 2012) - G.M. Guiry
Description: Filamentous; filaments unbranched, rarely solitary, usually in fine, smooth, layered to leathery strata (mats), microscopic and later macroscopic to several cm diam. usually covering substrates of different types divided in 3 subgenera (according to the frequency of sheath development): Gomontinema Anagnostidis and Komárek, Phormidium and Hansgirgia Anagnostidis and Komárek. Sheaths develop facultatively in different frequencies, only in suboptimal conditions (subg. Gomontinema), in dependence on changing environmental factors (subg. Phormidium), or regularly in all conditions (with exceptionally living free trichomes - subg. Hansgirgia); sheaths are tube-like, firm, colorless, joined to the trichomes, not layered, opened at the ends, containing always a single trichome. Trichomes isopolar, more or less straight, coiled or waved, usually 2-12(14) _m wide, uniseriate, never branched, composed of cylindrical to slightly barrel-shaped cells, more or less isodiametric or slightly shorter or longer than wide, constricted or unconstricted at the crosswalls, not attenuated and bent or screw-like twisted towards the ends, motile (waving, creeping, oscillations) within and out of sheaths. Cells without aerotopes or exceptionally with aerotopes under special, suboptimal conditions (but never characteristic of planktonic species), sometimes with granular content or with prominent granules spread throughout the cell volume, or agglomerated at the crosswalls; end cells widely rounded, attenuated or pointed, sometimes with calyptra. Cell content usually blue-green, rarely brownish, pinkish or violet, sometimes modifications with stable PE:PC ratio occur; thylakoids situated perpendicular to the cell wall (radially in a cross section). Heterocytes and akinetes absent. Cell division crosswise, perpendicularly to the long axis of a trichome, daughter cells grow Å to the original size before the next division. All cells capable of division with the exception of apical ones, sometimes indistinct meristematic zones occur. Reproduction by variously long, Å motile hormogonia, which separate at the end parts of trichomes by help of necridic cells or by fragmentation of whole trichomes (also with necridic cells). Rarely solitary filaments, usually in mats on different aeric or aquatic substrates (soil, wet rocks, mud, aquatic plants, stones and woods in both stagnant water and streams), some species occur in the marine littoral. Several species are known from extreme localities (thermal springs, desert soils, etc.), few of them take part in the biolithogenic processes and form travertine crusts in limestone water biotopes.
Information contributed by: J. Komárek. The most recent alteration to this page was made on 3 Mar 2023 by M.D. Guiry.
Numbers of names and species: There are 423 species names in the database at present.
Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):
Click here to also show infraspecific names in the list below.
References
Thomazeau, S., Houdan-Fourmont, A., Couté, A., Duval, C., Couloux, A., Rousseau, F. & Bernard, C. (2010). The contribution of sub-Saharan African strains to the phylogeny of cyanobacteria: focusing on the Nostacaceae (Nostocales, Cyanobacteria). Journal of Phycology 46(3): 564-579.
Verification of data
Users are responsible for verifying the accuracy of information before use, as noted on the website Content page.
Contributors
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.
Created: 28 December 2000 by M.D. Guiry
Verified by: 03 March 2023 by M.D. Guiry
Linking to this page: http://admin.algaebase.org/search/genus/detail/?genus_id=43079
Citing AlgaeBase
Please cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2025. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 22 June 2025.
