Fungal mutualisms with simple algae or cyanobacteria.

Lichens are partnerships, with the fungi essentially providing a home along with protection (and water and ) for its photosynthetic partner, and the latter providing the products of photosynthesis and even of nitrogen fixation.

Lichen are important ecologically because of there ability to otherwise unexploited environments () leading to ecological successsion as well as to serve as for certain animals (e.g., ). They reproduce either via or the production of soredia.

Lichens represent a pre-plant invasion by photosynthesis of terrestrial environments. The fungal-algae symbiosis seen with lichens can also be viewed to a degree as analogous to the mycorrhizal-plant symbiosis.