Peltigera didactyla

Lichen are good measures of air quality as they are very sensitive to pollution, in particular sulfur dioxide. Their sensitivity to this air pollutant is so great that it has been possible to calculate the amount of atmospheric sulphur dioxide by mapping the occurrence or disappearance of certain lichens in a given area. They are also very sensitive to nuclear radiation and can be used to monitor radioactive contamination.

Many lichens have antibiotic properties and are used to treat various ailments. One type in Europe is used to treat tuberculosis, while others are used to produce salves effective in treating cuts and skin diseases.

Lichens have also been used as dyes. Greeks, Romans and Native Americans all utilized lichens to make dyes of all colours.