Isactis Thuret ex Bornet & Flahault, 1886
Holotype species: Isactis plana Thuret ex Bornet & Flahault
Original publication and holotype designation: Bornet, E. & Flahault, C. (1886 '1887'). Revision des Nostocacées hétérocystées contenues dans les principaux herbiers de France (deuxième fragment). Annales des Sciences Naturelles, Botanique, Septième Série 4: 343-373.
Request PDFDescription: Filamentous-thallose; thallus flat, covering the substrate as an irregular crustose monolayer or of dark green or blackish spots, with heteropolar filaments, arranged parallel and densely into one-layered stratum, oriented perpendicular to the substrate. Trichomes straight or slightly waved, uniseriate, with basal heterocytes, more or less cylindrical from the basis along the main part of the whole trichome length, in the apical part successively narrowed and elongated into short or long, cellular hair; with intense constrictions at crosswalls. Sheaths fine, gelatinous, indistinctly stratified, colorless or yellow-brown, soon gelatinous, diffluent and confluent together (trichomes are at last embedded by gelatinous mass, striated parallel with trichomes - rests of gelatinous sheaths). False branching in upper part of trichomes; separated trichomes remain parallel, joined to the original one, but not in direct connection. Cells barrel-shaped, in the hair cylindrical, with blue-green, slightly granular content. Heterocytes basal, hemispherical or spherical, before false branching also intercalary, which usually soon obtain the spherical form. Akinetes missing. Cells divide perpendicular to the trichome axis, probably along the whole length with exception of a hair (no meristematic zones were recorded). Reproduction by hormogonia, escaping from the thallus. Two species are marine, growing on rock surfaces and epiphytic on algae in shallow beaches (one cosmopolitan ?, one known from Japan), one species grows on wood and rocks in the splash zone of littoral of clear streams in Finland.
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 feminine.
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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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.
Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=43090
Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 06 March 2023. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 23 April 2024
