Lichens - More Than Meets the Eye
Gail Ruhl, Senior Plant Disease Diagnostician,
Director, Purdue University
As deciduous trees stand bare, the greenish "scaly" growth
of lichens on tree trunks and branches becomes more visible.
Questions often arise regarding the health of trees in relation
to the presence of lichens. Many, unaware of the unique composition
of lichens, wonder if the lichens will harm the trees.
Lichens are not harmful to trees. As per the following website, Lichens of
North America at http://www.lichen.com/,
lichens are composite, symbiotic organisms made up from members of as many
as three kingdoms. The dominant partner is a fungus. Fungi are incapable of
making their own food and thus usually provide for themselves as parasites
or decomposers. The lichen fungi (kingdom Fungi) cultivate partners that manufacture
food by photosynthesis. Sometimes the partners are algae (kingdom Protista),
other times cyanobacteria (kingdom Monera), formerly called blue-green algae.
Some enterprising fungi exploit both at once.
Lichens live as one organism, both inhabiting the same body
and are merely using the trees as a place to anchor.
Lichens occur in a variety of habitats from the Arctic to the Antarctic and
all regions in between. One may find them on exposed rocks in the deserts,
on solidified lava flows in Hawaii, on frozen substrata in arctic regions,
on the bark of trees, and on the leaves of plants. It has been reported that
there are more than 3600 species of lichens in the United States and Canada.
Some lichens are flat and appressed to the growing surface while others may
appear leaf or shrub-like. http://www.lichen.com/vocabulary.html.
Lichens can serve as indicators of air pollution. In centers of heavy industrial
pollution, it has been observed that few to no lichens can be found. Lichen
populations have been shown to increase gradually with distance from these
centers and are thus used in ecological studies as a measure of pollution intensity.
For more information on lichens you may want to check out the
following web site: LichenLand http://mgd.nacse.org/hyperSQL/lichenland/.