The incorporation of the cyanobacterium Nostoc by the Zygomycete Geosiphon is the only known example of an extant endosymbiosis between a fungus and a cyanobacterium. It is regarded as a model for the origin of plants. The fungus is also closely associated with mosses with which it can co-exist in a symiotic, mycorrhiza-like relationship, as established by recent research. In addition, its endosymbiotic partner Nostoc lives symbiotically within the thallus of mosses in this biocenosis....