Lichens

A lichen is not a single organism but a partnership: a fungus provides shelter while algae or cyanobacteria living inside it make food from sunlight. This teamwork lets lichens grow on bare rock, tree bark, old walls and Arctic tundra, where few other living things can survive. Because many lichens absorb moisture and pollutants directly from the air, they are often used as indicators of air quality.

Start with our introduction to lichen, then learn to tell apart the main growth forms: leafy foliose lichen, flat, crusty crustose lichen and shrubby fruticose lichen. These guides make a great starting point for nature walks and school science projects.