Lichens on rock D. Dougall

Lichens are small plants that are made up of two components – a fungus and algae. The fungus provides the structural components of the plant, while the alga provides nutrition and energy via photosynthesis. Lichens lack true roots, stems and leaves, although some forms grow to resemble these common plant parts. Lichens reproduce using spores or detachable fragments.

Lichens grow on surfaces such as rock, tree bark, or other substrates, and obtain most of their nutrients from the atmosphere. Because lichens gather materials that are washed from the air by precipitation, they can be used to monitor certain pollutants that travel through the air, such as heavy metals and sulfur. There are many species of lichens, and upon close inspection you can see the differences in color and shape. When viewed from a distance however, they often create a more uniform coloration of yellow, green or brown, that "paints" the surface of the rocks and cliffs.