When it is 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; hence the popular names, star jelly, troll’s butter, witch's butter (not to be confused with the fungus Tremella mesenterica), and witch’s jelly.
This and other species in the genus contain a green algae in the genus Coccomyxa and also cyanobacteria in the genus Nostoc as symbionts.
Nostoc |
Bacteria that do associate with plants include the actinobacteria Frankia, which form symbiotic root nodules in actinorhizal plants, and several cyanobacteria (Nostoc) associated with aquatic ferns, Cycas and Gunneras.