Recently I gave a lecture about nature photography to a group of young people. I was surprised by their knowledge of plants and animals and they easily identified most species I showed them.
However, what surprised me most was the fact that none of them could tell me what a lichen is.
Lichens are common organisms that grow in the most unusual places including bare rock and walls, even in urban areas. About 200 lichens have been recorded in the Maltese islands but I am sure that, with some effort, more unrecorded species can be found.
Lichens are unusual because each species is made up of two organisms, a fungus and an alga, living intimately together. This gives lichens the ability to survive under harsh conditions where no other organism can survive. In some cases the fungus and alga which make up a lichen can be found living separately in nature but, in many cases, the two organisms have become so dependent on each other that one cannot survive without the other.
Lichens do not have leaves or roots and absorb nutrients directly through their surface. This leaves them susceptible to air pollutants which accumulate in their body without being eliminated.
Lichens can tolerate different concentrations of pollutants with some species dying at lower levels than others. This makes lichens excellent biomonitors and many species are used to indicate levels of environmental pollutants.
Many species of lichens are eaten especially in times of famine despite the fact that they can be difficult to digest. Many species also contain mildly toxic compounds, although few species are poisonous.
Some species are used to produce dyes including the pH indicator litmus.
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