Lichen is a perfect example of mutualism. The fungus benefits from the symbiotic relation because algae or cyanobacteria produce food by photosynthesis. The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungus, which also gather moisture and nutrients from the environment, and (usually) provide an anchor to it.

The leaf-like branches, flat leaf-like structures and flakes lying on surface are called fruticose, foliose and crustose, respectively.

The lichen which grows like powder dusted on rocks is called leprose lichen.

Lichens are very sensitive to environmental disturbances and are not found in polluted areas.

The shape of a lichen is usually determined by the organisation of the fungal filaments.

When a crustose lichen gets old, the centre may start to crack up like old-dried paint. This is called being rimose or areolate, and the island pieces separated by the cracks are called areolas.

Special pigments give lichens a variety of colours, including red, orange, yellow and brown, especially in exposed, dry habitats.

The most common fungal partner in lichens is ascomycetes, which produce reproductive spores in special cells shaped like sacs.

In lichens, the fungal filaments surround the algal cells.

Wolf lichen is a poison.

Lichenometry is a technique used to determine the age of exposed rock surfaces based on the size of lichen thalli. 

The lichens that produce fruiting body apothecium are called Gymnocarpae.

In lichens that include both green algal and cyanobacterial symbionts, the cyanobacteria may be held on the upper or lower surface in small pustules called cephalodia.

Ursolic acid inhibits the growth of human epidermoid carcinoma cells by affecting tyrosine kinase activity.

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