Reindeer lichen. Clump of Cladonia rangiferina lichen. This foliose (leafy) lichen is commonly known as reinder lichen, or reindeer moss. Lichens are symbiotic organisms formed of a fungus and an alga that mutually benefit one another. The alga is contained within the hyphae (filaments) of the fungus. They are therefore protected from harsh conditions, and in particular from dessication. The alga supplies the fungus with nutrients that it makes by photosynthesis.