You won’t find many garden designers who write about lichens. They are very important environmental indicators. They tell us whether the air is clean or polluted. They are particularly sensitive to sulphur dioxide gases. If you find lots of shrubby lichens, covering the bark and twigs on your garden trees and you can be sure the air is clean. Find a dearth of lichens or a few miserable powdery types and you can be equally sure that your air has been polluted. Of course it makes sense to search for lichens on established trees and not one that you planted last week; they take time to grow. They also grow on roofs, cemetery gravestones and concrete posts. The species also vary according to the building material that is available to them. They like damp conditions so look for them especially on north facing walls.
Lichens are composed of two organisms: an alga and a fungus. These organisms are symbiotic, living in a close mutually beneficial partnership. Because they are sensitive to sulphur dioxide pollution they don’t do well in heavily polluted areas. In fact lichens are more sensitive to pollution than any other plant.
Organisms that tell us something about the environment in which they live are called biological indicators. These indicator species tell us how healthy our planet is. So it is worth keeping a look out for them; so what do they look like? Lichens come in different forms some are bushy, shrubby and even crusty. They live on walls, roofs, tree trunks, twigs and branches. The orange whorls on roofs and gravestones are Xanthoria lichens.
Examples of lichens you might find in your garden include Lecanora muralis which seems to be the most common. Lecanora muralis is a waxy looking, pale yellowish green crustose lichen that usually grows in rosettes radiating from a centre filled with disc-like yellowish-tan fruiting bodies. Then there is the lovely orange growths of Xanthoria, these are among the commonest and most attractive on garden walls. You may even find the lawn inhabiting dog lichens, Peltigera.
‘Reindeer Moss’ is not a moss. It is a lichen! These Cladonia are a group of moss-like lichens. They are the primary food source for reindeer/caribou. Cladonia species are of economic importance to reindeer-herders, such as the Sami in Scandinavia or the Nenets in Russia. When Chernobyl blew its top in 1986, the radionuclides attached very strongly to this lichen and reindeer was off the menu for a few years for the Sami culture and others in Norway, Finland, Sweden and Russia.
So go check out the lichens in your garden. Search the trees and walls. Find out how clean your air is!