Nostoc

Nostoc is a genus of fresh water cyanobacteria that forms spherical colonies composed of filaments of moniliform cells in a gelatinous sheath. When on the ground, a Nostoc colony is ordinarily not seen; but after a rain it swells up into a conspicuous jellylike mass, which was once thought to have fallen from the sky, whence the popular names, fallen star and star jelly. It is also called witches' butter. Michael Quinion of the World Wide Words newsletter says that it is known in Welsh as pwdre sêr, or rot of the stars.

It can be found on moist rocks, at the bottom of lakes and springs, and rarely in marine habitats. It may also grow symbiotically within the tissues of plants, such as the aquatic fern Azolla (mosquito fern) or hornworts, providing nitrogen to its host. These bacteria contain photosynthetic pigments in their cytoplasm to perform photosynthesis.

Species
Nostoc is a member of the family Nostocaceae of the order Hormogonales. Species include:


 * N. azollae
 * N. caeruleum
 * N. carneum
 * N. comminutum
 * N. commune
 * N. ellipsosporum
 * N. flagelliforme
 * N. linckia
 * N. longstaffi
 * N. microscopicum
 * N. muscorum
 * N. paludosum
 * N. pruniforme
 * N. punctiforme
 * N. sphaericum
 * N. spongiaeforme
 * N. verrucosum

Culinary use
Containing protein and vitamin C, Nostoc species are cultivated and consumed as a foodstuff, primarily in Asia. The N. flagelliforme and N. commune varieties are consumed in China, Japan and Java. The preferred variety in Central Asia is N. ellipsosporum.