Lichen is a symbiotic association between a fungal and an algal partner.

 

Lichens are a symbiosis of a heterotrophic fungal partner and a photosynthetic algal component. The fungi in the lichen provide inorganic components to the algae whereas algae photosynthesize food and provide it to the fungi. Symbiosis is the interaction between two different organisms living in close physical association that benefit from each other.