Download Lichens are organisms that are formed by the

Lichens are organisms that are formed by the symbiotic
relationship between fungi and algae. Symbiosis is a
mutually beneficial association that occurs between
two different species. In the case of lichens, the alga,
which contains chlorophyll, provides the fungus with
sugars produced by photosynthesis, while the fungus
releases water and mineral nutrients to the alga, at the
same time protecting it from too intense light, drought
and excessive heat. Together they can survive in
extreme environments (high altitude rocks, deserts,
etc) where they would not be able to live on their own.
Depending on their shapes, lichens are divided into
crustose, foliose and fruticose.
Within the forest (particularly in coniferous forests,
where microorganisms find it hard to attack and
decompose the acidic litter that is produced therein)
they play a very important ecological function since
the rapid proliferation of lichens in a moist environment
provides the soil with a continuous supply of herbaceous
organic material which is crucial to its fertilization.
Lichens are amongst the first organisms to colonize
bare surfaces and are able to thrive also in extreme
temperatures. However, since they lack a secretion
system, lichens are very sensitive to air pollution.
This characteristic makes them excellent biological
indicators, which are increasingly used in biomonitoring
of air quality.