Nostoc is not a plant, it is a type of blue-green algae or cyanobacteria, one of the most primitive of organisms. Some scientists believe these organisms produced the first oxygen for Earth's early atmosphere. Nostoc is also a nitrogen fixer, it can take N2 from the air to be used in symbiotic relationships with mosses, ferns, lichens and other fungi. This kind grows on the ground. It is soft and mushy when it is wet, when it is dry it is black, and brittle.