Nostoc(redirected from nostocs)
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a genus of blue-green algae of the class Hor-mogonaceae. There are approximately 50 species, living in almost all climatic zones, in fresh waters and on damp cliffs and soil. Colonies of the algae are gelatinous and spherical, with a diameter of up to 10 cm. They resemble tapes or filaments and are free-living or sedentary. The colonies consist of single rows of filaments buried in the slime. Each filament is composed of thick-walled cells called heterocysts. The algae reproduce by spores or vegetatively, with bits of the filaments breaking off. There are some nitrogen-fixing species. Some species of Nostoc are used as food in Asian countries.