Physcia pumilior

Lichens consist of a mutualistic association between a fungus and an alga (or cynaobacterium). The fungus gives the lichen structure, while the algae provides food. Technically, in mutualistic symbiosis, both organisms should benefit - the fungus receives sugars from the photosynthetic activities of the alga, while the alga receives a safe place to live. However, in reality, studies show that this dual organism is probably a controlled parasitism of the alga by the fungus.