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Lichens

Lichens are a symbiotic association of a fungus and an alga.  Effectively, some of these associations are so close that the lichen can be considered as a single organism.

How Lichens Work

In a lichen, the visible body of the plant is the fungus although the colour is often caused more by the algae enclosed by the cells.  The fungus holds the organism together and gives it its physical form. It absorbs water and other nutrients that both parts use.

The Alga part of the relationship photosynthesises and converts Carbon Dioxide and Water into forms of energy that both partners of the lichen can use.

Habitat

Lichens will often grow in places no other plant can use.  They are frequently found growing on solid rock in a huge variety of climates including the dry valleys of Antarctica and the faces of Mount Rushmore.

They will grow on soil, even in deserts. The green growths on tree trunks are often lichen.

Temperature Flexibility

Experiments have shown that even the tropical species of lichen tested can continue to function at minus forty degrees C (minus forty degrees F).

Reproduction

Different species of lichen reproduce differently.  Some of them have diaspores including both the organisms in the lichen.

Survival in Outer Space

The European Space Agency found 15 days exposure of the vegetative part of lichen did not affect it.  It is reasonable to expect that the diaspores will be at least as resistant, and probably much more so.

Drying out

Lichens will survive in an apparently totally dry state,and will revive in a few minutes with water.

Water Absorption

The fungus part of the lichen gets the water, and it is very good at it.  Rain, dew and even water vapour are used by this tough plant.

Space Travelling Lichens

We have no definite proof of living things on any planet other than the Earth, but lichens are one plant that has been suggested as growing on Mars.  Although the Mars Landers did not find any lichens, this certainly does not rule out the possibility that they have got to Mars and have colonised favourable habitats on our neighbouring planet.

Lichens are believed to be ancient forms of life.  Although it might take an apparently unlikely series of events for a diaspore or vegetative part of a lichen to get to Mars, they have had several hundred million years to do it.

It is worth remembering that even on Earth; people have often been amazingly slow to recognise the presence of life in unexpected places.


 
Yellow Lichen on a rock in Newfoundland in Canada
Photo by Neelix
 
 
 
A red lichen (Cryptotheria rubcinta) on a tree.
"The Christmas Lichen", growing on standing bootless Sabal palmetto tree, Myakka River State Park, Sarasota Co., Florida.     Photo by Neil Dollinger.
 
 
"Reindeer Moss" is a Lichen; Cladonia rangiferina.  It is a very important winter food for Reindeer, but very slow growing and if it gets puuled out completely takes decades to re-establish itself.  This important plant is being threatened by the warming of the Arctic.  If rain comes and freezes into ice before the snow comes, the Reindeer pull out the whole plant instead of just eating off the top.
Photograph by the U.S. Fish and Wildlife Service.