Nostoc commune is a terrestrial or freshwater, colonial species of cyanobacterium with a cosmopolitan distribution. It is able to survive in extreme conditions.
Nostoc commune is a slime which swells up into a jelly-like mass when wet. It forms loose clumps on soil, gravel, paths, among mosses, wall bases and inside plant pots. It can suddenly appear after rain and an early belief was that it was material from shooting stars that had fallen to earth, hence some of the common names.
Nostoc commune initially forms a small, hollow gelatinous globule which grows and becomes leathery, flattened and convoluted, forming a slippery, gelatinous mass. Within its outer membrane, the colony contains a brownish gel which does not have chloroplasts but contains photosynthetic pigments in the cytoplasm of the cells. The gel also contains pigments that absorb long and medium wavelength ultraviolet radiation, which enables it to survive in places with high levels of radiation. The colonies vary greatly in appearance according to how wet they are, but they are generally a bluish-green, olive-green to brown. In dry conditions, it becomes an inconspicuous, crisp brownish mat.
Nostoc commune can fix nitrogen from the atmosphere and can, therefore, live in locations where no nitrogenous compounds are available from the substrate. Under adverse conditions, Nostoc commune can remain dormant for an extended period of time and revive when conditions improve and water becomes available. The desiccated colony is resistant to heat and to repeated patterns of freezing and thawing.

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Nostoc commune (Star slime)