A lichen is a composite organism that emerges from algae or cyanobacteria living among the filaments (hyphae) of a fungus in a mutually beneficial (symbiotic) relationship. The fungus benefits from the algae or cyanobacteria because they produce food by photosynthesis. lichen is a composite organism that emerges from algae or cyanobacteria living among the filaments (hyphae) of a fungus in a mutually beneficial (symbiotic) relationship. The fungus benefits from the algae or cyanobacteria because they produce food by photosynthesis.