ON EARTH IS A LICHEN?
by Whit Gibbons
October 14, 2007
found a life form that keeps my grandson searching through the backyard
or woods, no matter where we are. It doesn't bite, sting, or pinch, so
I don't worry when he finds some and brings them back. They come in many
colors, although green and gray seem to be the most common. Plus, it's
kind of cool to hear a four-year-old say "look at the lichens."
is a lichen? Although appearing to be a single organism, a lichen 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. 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,
my grandson and 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,
natural 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, including moths, slugs, and mites.
Hummingbirds, vireos, and other birds use lichens for nest material. Lichens
are even used by humans, such as for dyes, antibiotic salves, and perfumes.
Litmus paper, which can determine the acidity of a liquid, is made from
a species of lichen. And the alpine reindeer lichen is used to make tiny
little trees for model railroad displays.
us pay no attention to lichens, yet they are an important and fascinating
part of the living world in your yard, local parks, and woods. 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. That's one of the
things I'm trying to teach my grandson.
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