ON EARTH IS A LICHEN?
by Whit Gibbons
April 4, 2004
feature of ecology is the endless interaction among plants, animals, and
the inanimate world. In fact, so much life swirls around us that we take
some life forms for granted and give them little thought. Among the under-appreciated
organisms are the lichens.
is a lichen? Although a lichen appears to be a single organism, a lichen
species actually represents a complex relationship between a fungus and
algae. The species live together in a permanent symbiotic partnership
in which each provides for the other, whereas neither could persist alone.
fungal and algal species contribute to their joint survival in special
and essential ways. Like higher green plants, algae convert sunlight into
usable energy through photosynthesis, a process a fungus cannot perform.
But the fungi are able to absorb vital nutrients from the surface they
grow on. Hence, algae offer energy to the association; fungi supply minerals.
Also, the fungal structure protects the algae from exposure. Ultimately,
both species benefit, resulting in a single living organism.
notice lichens, but they are easy to find. To check this out for myself,
I walked outside and found lichens on almost every surface-bricks and
concrete walls, tree bark, rocks, and the ground itself. Lichens are everywhere!
Next time you see what appears to be a bare cliff face or rock wall, take
a closer look. You will find lichens anchored into the rock itself. Many
oaks and other trees have patches of greenish or gray lichens that may
be spongy or flat and dry. As a rule, lichens cause no harm to the plants
they attach themselves to.
are found in a variety of habitats throughout the world. The lichen known
as reindeer moss is eaten by caribou in northern alpine and arctic regions.
The lichen carpet in some regions of tundra provides the major source
of food and nutrients for the big herbivores, which in turn are a primary
food source for wolves. Odd to think that such an awesome predator ultimately
depends on a combination of a fungus and algae.
17,000 species of lichens have been described, most belonging to the fungus
group that includes the edible morel mushrooms. What might seem to be
a fragile life form may actually be one of the toughest organisms around.
Lichens not only persist on tundra and mountain cliffs but also inhabit
hot deserts and Antarctic sea water. But natural conditions do not have
to be harsh for lichens to thrive. They can be found in old growth forests,
wetlands, and prairies.
the durable lichens are believed to be highly sensitive to some components
of modern air pollution. They have been reported to be intolerant of toxic
materials such as sulfur dioxide, heavy metals, and fluorine. Lichens
have even been proposed for use as indicators of air pollution in areas
with high pollution from industrial sources. One report noted a gradual
decrease in lichen abundance from the outskirts of an industrial area
to its center.
serve as a food source for many animals besides caribou, such as moths,
slugs, and mites. The bright colors on the wings of tiger moths are thought
to warn bird predators that, because the moth caterpillars eat lichens,
the adult moths are distasteful. Hummingbirds, vireos, and other birds
use lichens for nest material. Lichens are even used by humans, such as
for dyes (including those used in Harris tweeds), antibiotic salves, and
perfumes. Litmus paper, which can determine the acidity of a liquid, is
made from a species of lichen. And a lichen species known as the alpine
reindeer lichen is used to make tiny little trees for model railroad displays.
most of us pay no attention to lichens, they are an important and fascinating
part of our natural world. They are on the trees, logs, and rocks in your
yard and local parks. Look for the pale greenish or gray coating, sometimes
in little patches, on tree trunks, large rock faces, or on the soil itself.
It's gratifying to know that two completely different, little noted life
forms can live in harmony to make another that is so persistent and pervasive.
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