Nostoc Vaucher ex Bornet et Flahault 1886: 181.
Type species: Nostoc commune Vaucher ex Bornet & Flahault
Source: Komárek, J., Kling, H. & Komárková, J. (2003). Filamentous Cyanobacteria. In: Freshwater Algae of North America. (Wehr, J.D. & Sheath, R.G. Eds), pp. 177-196. San Diego: Academic Press.
Classification: Empire Prokaryota Kingdom Bacteria Subkingdom Negibacteria Phylum Cyanobacteria Class Cyanophyceae Subclass Nostocophycideae Order Nostocales Family Nostocaceae Genus Nostoc
Description: Thallose; thallus micro- or macroscopic gelatinous, amorphous or spherical, later irregularly spherical, lobate, smooth or warty on the surface, filamentous or forming flat gelatinous or "paper like" (when dry) colonies, usually with distinct periderm on the colonial surface. Filaments within colony irregularly coiled and loosely or densely agglomerated, sometimes more gathered in peripheral layer; sheaths around trichomes present, but visible usually only in the periphery of colony or in young colonies, wide, fine mucilaginous, confluent with colonial mucilage, sometimes yellowish-brown. Trichomes isopolar, of the same width along the whole length, apical cells morphologically not different from other cells; cells cylindrical, barrel-shaped up to almost spherical (forming moniliform trichomes; variability of cell size and shape sometimes distinct in one and the same species). Heterocytes solitary, develop in trichomes terminally or intercalary (their frequency or absence is dependent on nitrogen metabolism); trichomes in principle metameric. Akinetes arise apoheterocytic, oval, little larger than cells; almost all cells between heterocytes change successively in akinetes towards heterocytes. Nostoc has special life (vegetation) cycle, during which forms several special and characteristic stages (Mollenhauer 1986, Lazaroff 1972, Komárek and Anagnostidis 1989). From several described subgenera are probably acceptable typical Nostoc and Amorphonostoc, which differ in morphology of colonies (Amorphonostoc has no periderm) and by a type of life cycle, which is simpler in Amorphonostoc. Cells divide crosswise. Reproduction by motile hormogonia, which differentiate from trichomes by disconnection at heterocytes, by dissociation of thallus and by akinetes, respectively. Different species grow in freshwater biotopes, epipelic, epilithic and epiphytic in unpolluted lakes, ponds and pools, many species grow in different soils (especially the subgenus Amorphonostoc) or on their surface. N. flagelliforme from Chinese semideserts is edible. Several species are important components of subpolar soil or water biotopes and nitrogen fixers. Few species grow endophytically in fungi (Geosiphon), mosses, liverworts, ferns and vascular plants (roots of Cycas, Gunnera). In world collections are numerous isolated strains, which are, however, insufficiently identified
Numbers of names and species: There are 331 species names in the species database at present, of which 55 is/are flagged as current.