|
Lichens:
Lichens
are symbiotic relationships between a fungus and algae
or a cyanobacterium housed by the fungus in a thallus.
As the algae or cyanos can live independent of the
fungi but not the reverse in nature, it is thought
that the fungus is parasitizing the photosynthetic
partner. There are 20,000 species of lichens! The
fungal component is the unique feature as 90% of the
photosynthetic partners come from only 5
genera.
They
grow very slowly, 0.1 - 1mm a year. Thus large lichens
found in nature are estimated to be incredibly old --
4,500-5000 years. They can grow in the most extreme
environments - in the arctic, the deserts, on trees or
any surface for that matter (glass, plastic). Yet in
the last few decades a noticeable reduction of their
growth has been noted in those sites with air
pollution. Thus they are now used as indicators of
pollution or biomarkers.
The
thallus consists of layers of hyphae of an ascomycete (
and in a few cases of a basidiomycete). The top layer is
made up of tightly knit hyphae forming a protective
barrier, below which the photosynthetic organisms live.
Below them the hyphae are loosely knit, demarcated by a
substrate layer which again can be made up of more
compacted hyphae.
|
|
|
images taken by botany
students
|
|
|
 note
the green hyphae and the red algal component
|
Most reproduction is asexual. Fungi
do reproduce sexually. When this occurs the hyphae must meet up with
an appropriate algal partner to form the lichen.
II. There are four major growth
forms, only 3 of which will cover: How may these forms allow a lichen
to better fit in with its' environment?- One form resembles a crust
that's closely attached to the surface.
They're quite drought resistant and
do well in dry or extreme climates like deserts, Arctic, Alpine
regions, and ice-free Antarctic areas.
- "Leafy" lichens grow best in places
with frequent rainfall, and are also found on rocks in freshwater
streams.
- Stalked or filamentous lichens are
common in humid foggy areas like seacoasts and mountainous
tropics.
Foliose lichen
Uses of lichens: adapted from:
http://www.tesarta.com/www/resources/library/lichens.html and
http://www.earthsky.com/1998/esmi980708.html
For a nice pictorial view with great
info also see:http://www.lichen.com/home.html the North American
Lichen Project
Food
Arctic and subarctic lichens are food
for many mammals, including caribou and moose. Mountain sheep and
mountain goats eat them, as do prong-horn antelope, and domestic
sheep. In the Middle East certain lichens were used to make a type of
nutritious bread.
Medicine and Poison: lichens
produce over 500+ biochemicals some as secondary compunds for defense
- or at least we assume since they have antimicrobial
properties..
In earlier times , lichens were used
medically based on their look or where they were found.
- Lungwort was used to treat
tuberculosis, pneumonia and other lung ailments.
- Yellow lichens were used to treat
jaundice, a disease which yellows the skin.
- Dog lichen, the fruit of which
looks like teeth, was supposed to treat rabies.
- The skull lichen (usually found
on rocks but sometimes on skulls) supposedly treated
epilepsy.
- "Iceland moss" has been used to
treat coughs and chest ailments for the past 230
years.
Usnic and other acids, found in many
lichens, have antibacterial qualities and are still used in some
antibiotic creams. Some lichens are used to create alcohol. Wolf
lichen is a poison, used in Russia to poison wolves. Certain Native
American tribes also used Wolf lichen to treat skin problems. Other
lichens contain selenium, which is poisonous to livestock.
Perfumes and Dyes
Many European and Northwest American
lichens are used to create perfumes -- not as the scent itself but as
an additional ingredient to control evaporation.
Litmus paper uses a lichen-derived
dye.
Other lichens have been used for wool
and silk dyes, making browns, yellows, reds and similar colors.
Orchil is a well-known lichen dye that has a red-violet color, and is
used in food coloring. A type of lichen found on coastal rocks in the
Mediterranean was used in ancient times to create some of the royal
purple dyes.
The wools are dyed with lichens
pigments to produce the rich yet muted colors we find in jackets and
scarves from Scotland and Ireland..Also native indians from Alaska
through the SW have and continue to use lichen dyes for
weavings.
Pollution
indicator:
Lichens have been used to analyze air
pollution as they absorb atmospheric pollutants.These concentrations
are they anaylzed by quantitative analytical techniques.. Lichens are
quite sensitive to air pollutants and have been used as indicator
species in polluted areas.