|Class:||see taxonomic note|
Vaucher ex Bornet & Flahault, 1888 
Nostoc commune is a species of cyanobacterium in the family Nostocaceae. Common names include star jelly, witch's butter, mare's eggs, fah-tsai and facai. It is the type species of the genus Nostoc and is cosmopolitan in distribution.
Nostoc commune is a colonial species of cyanobacterium. It initially forms a small, hollow gelatinous globule which grows and becomes leathery, flattened and convoluted, forming a gelatinous mass with other colonies growing nearby. Inside the thin sheath are numerous unbranched hair-like structures called trichomes formed of short cells in a string. Cells have no nucleus nor internal membrane system. To multiply, they form two new cells when they divide by binary fission. Along the trichomes, larger specialist nitrogen-fixing cells called heterocysts occur between the ordinary cells. When wet, Nostoc commune is bluish-green, olive green or brown but in dry conditions it becomes an inconspicuous, crisp brownish mat.
Distribution and habitat
Nostoc commune is found in many countries around the world. It is able to survive in extreme conditions in polar regions and arid areas. It is a terrestrial or freshwater species and forms loose clumps on soil, gravel and paved surfaces, among mosses and between cobbles. In Singapore, Nostoc commune is found growing on alkaline soils, in brackish water, in paddy fields, on cliffs and on wet rocks.
Nostoc commune can fix nitrogen from the atmosphere and can therefore live in locations where no nitrogenous compounds are available from the substrate. Nostoc commune does not have chloroplasts but contains photosynthetic pigments in the cytoplasm of the cells. It also contains pigments that absorb long and medium wavelength ultraviolet radiation, which enables it to survive in places with high levels of radiation.
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 and produces no oxygen while dormant. It has been found that extracellular polysaccharides are vital to its stress tolerance and ability to recover.
Nostoc commune is eaten as a salad in the Philippines and is also eaten in Indonesia, Japan and Taiwan. In Taiwan, it is nicknamed "yu-lai gu" (meaning post-rain mushroom) or "tsao-di er" (meaning meadow ears). Nostoc commune var. flagelliforme is known as "facai" in China which forms part of the food traditionally served at the Lunar New Year.
- Guiry, M.D.; Guiry, G.M. (2012). "Nostoc commune - Vaucher ex Bornet & Flahault". AlgaeBase. Retrieved 2012-09-08.
- Wee Yeow Chin. "Nostoc commune". Raffles Museum of Biodiversity Research. Retrieved 2012-09-07.
- "Nostoc". MicrobeWiki. Retrieved 2012-09-08.
- Tamaru, Yoshiyuki; Yayoi, Takani; Yoshida, Takayuki; Toshio, Sakamoto (2005). "Crucial Role of Extracellular Polysaccharides in Desiccation and Freezing Tolerance in the Terrestrial Cyanobacterium Nostoc commune". Applied and Environmental Microbiology 71 (11): 7327–7333. doi:10.1128/AEM.71.11.7327-7333.2005.