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Isactis

Generic name: ISACTIS Thuret ex Bornet et Flahault 1886. Ann. Sci. Nat. Bot., ser. 7, 4: 341.
Synonyms: [ ISACTIS Thuret, Essai de classification des Nostochinees, p. 11, 1885 (Ann. des sc. nat., 6e serie, Bot., I, p. 382) : Rivularia, Physactis, Dasyactis, Mastichonema, Zonotrichia spec.
Diagnosis:
Bornet et Flahault (1886): Thallus planus, crustaceus, orbicularis, tennis, pagina inferiori adnatus, ambitu crescens. Fila parallela erecta sim- plicia, rarius parce pseudoramosa. Heterocystae basilares. Sporae ignotae. Plantae marinae.
Type species: Isactis plana Thuret ex Bornet et Flahault 1886 
Descriptions:
Komárek (1992): Filamentous – thallous; thallus flat, covering the substrate in form of the irregular crustaceous monolayer or of dark green or blackish spots, with heteropolar filaments, arranged parallely and densely into one-layered stratum, oriented perpendicularly 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 successive narrowed and elongated in short or long, cellular hair with intense constrictions at cross-walls. Sheaths fine, gelatinous, indistinctly stratified, colourless or yellow-brown, soon gelatinizing, diffluent and confluent together (trichomes are at last embedded by gelatinous mass, striated parallely with trichomes - rests of gelatinized sheaths). False branching in upper part of trichomes separated trichomes remain parallely 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 intercalar, which usually soon obtain the spherical form. Akinetes missing.
Genotype differences, molecular
data:
Reproduction strategies, life cycles, cell division:
Komárek (1992):Cells divide perpendicularly to the trichome axis, probably along the whole length with exception of a hair (no meristematic zones were recorded). Reproduction by hormogonia, liberating from the thallus.
Ultrastructure:
Taxonomic position, higher hierarchy:
Cyanophyceae, Nostocales, Rivulariaceae
Notes to taxonomy, misinterpretations:
Ecology, ecophysiology, ecological significance:
Komárek (1992): Two species are marine, growing on stone surface and epiphytic on algae in shallow beaches (one cosmopolitan ?, one known from Japan), one species grows on wood and stones in the splash zone of littoral of clear streams in Finland.
Physiology and biochemistry:
Distribution, endemism, problematic
citations:
Reference strain:
Infrageneric scheme, species
concept:
List of species:
Isactis fluviatilis [Kützing] Kirchner in Cohn ex Wolle 1887
Isactis nipponica Hirose 1937
Isactis plana Thuret ex Bornet et Flahault l886

Unclear taxa:
Isactis caespitosa [Kützing] Wolle 1887
Isactis centrifuga Bornet in Collins 1901

Keys:
List of stains:
Drawings:
Application technology:
Literature:

  2.1 taxonomy: Geitler 1932, Geitler 1942, Hirose 1937, Komárek 1992
  2.2 cytomorphology:
  2.3 16S rRNA sequencing:
  2.4 biology and life cycles:
  2.5 ecology: