Download Lichens fact sheet

Lichens fact sheet
Golden Shields, Xanthoria
parietinar. Very common
on rocks, walls and trees,
often growing beneath bird
perches. One of the most
common lichens today in
our towns and cities,
including London!
What is a lichen?
Unlike trees, grasses and flowers, a lichen is not a single plant. Instead, it consists of two partners that live
together symbiotically - with both of them benefiting from the alliance. One partner is a fungus. The other is
a green alga or cyanobacterium, often called a blue-green alga.
The fungus and alga function as one organism. The alga is a green plant with chlorophyll that is able to use
sunlight to produce essential nutrients by photosynthesis that feed both partners. The fungus creates a
body, called a thallus, in which they both live. The fungus produces chemical compounds that may act as
sunscreen to protect the alga.
There are about 30,000 species of lichen worldwide, and they come in a dazzling variety of shapes and
colours. Some are almost invisible to the naked eye and grow as a crust on rocks, trees or soil. Others are
called beard lichens and these can be bushy or trailing, sometimes growing up to three metres in length,
and others are lobed and leaf-like. Colours range from dull grey-browns to brilliant yellows and bright
orangey reds.
Where do they grow?
Lichens grow just about everywhere. They cover 8 per cent of the land surface, including some of the most
extreme environments on Earth. Lichens flourish on rocky coasts and mountain summits, in icy polar
regions and steamy tropical rainforests. Some prefer a single type of habitat such as limestone or sand
dunes, while others are widespread and grow on different trees, soil and rocks.
Why are lichens useful?
Lichens are incredibly useful because they tell us about the health of our environment. Lichens are very
sensitive to air pollution. As a rule of thumb, the smaller the variety of lichens in an area, the more polluted
it is.
In the past, sulphur dioxide from coal burning and industry was the worst pollutant. It killed lichens, so
industrial areas with high levels of sulphur dioxide became lichen deserts. Levels have now dropped thanks
to clean air laws and lichens are re-colonising those areas.
Nowadays, the major pollutants are nitrogen compounds from road traffic and intensive farming. These
compounds don't destroy all lichens because some species positively thrive on nitrogen. So different
pollutants create different patterns of lichen growth and, by understanding them, scientists are able to chart
the health of our environment. Some lichens grow very slowly so that they can tell you about the history of
the substrate and the environment where you find them. They have been used as indicators of ancient
woodlands that have never been clear-felled.
Lichens are also useful to their neighbours, recycling nutrients used by other plants and providing homes
for spiders, mites, lice and other insects. Humans extract the most incredible range of wool dyes from
lichens and also eat some of the edible species, while drug companies use lichens to make antibiotics or
sunscreen cream.