Genotype differences, molecular data:
Reproduction strategies, life cycles, cell division:
Komárek & Anagnostidis (1998):Cells divide irregularly by binary fission in various planes, in pseudofilaments predominantly crosswise. The lengthwise division of apical cells in pseudofilaments resulting in pseudodichotomous divarication is a typical feature of the genus (fig. 610). Enlarged cells, which arise in different parts of thallus, sometimes divide into baeocytes. Reproduction bybaeocytes.
Komárek (1992):Cells divide irregularly in different planes; enlarged cells from different parts of thallus divide sometimes in nanocytes. Reproduction by nanocytes.
Nostoc environments are diverse and widespread over the globe; isolates have been found in fresh water, soils, and both extremely cold and extremely arid habitats. Their role as a nitrogen fixer in terrestrial ecosystems allow them to maintain symbiotic interactions with organisms including fungi, lichen, mosses, and ferns. They are largely protected from predation by their outer sheath covering and the large size of their colonies, which make them difficult for some algivores to ingest. Some types of Nostoc are edible, and are even considered delicacies in some regions; in China during holidays a black hairlike vegetative species, Nostoc flagelliforme or "fat choy", are consumed. However, these algae can also cause problems for humans by growth on sport turf and buildings, and can lead to unpleasant odors in drinking water. Some phenolic extracts from Nostoc are known as human pathogen inhibitors, and may in the future be valuable to scientists medicinally. Very rarely Nostoc have been found to be symbionts of terrestrial plants, such as species which colonize the root nodules of Hawaiian cycad Gunnera genus.