Science Notes: Lichen on Trees

We found lichen on many of the trees around the campus. And that’s very good for us, because lichens only grow where the air is clean. In the 1970’s there was almost no lichen to be found on trees in urban environments because of air pollution and acid rain.

Lichens are fascinating organisms. In fact they are not one organism at all. They are made up of a fungus and one or more algae living together in a mutually-beneficial relationship – a kind of mini-ecosystem. The fungus makes up most of what you see: it surrounds and protects the algae. In return the algae feed the fungus (which is unable to feed itself) by photosynthesis.

The beauty of lichens is not easy to see: you need at least a magnifying glass to appreciate them, but an electron microscope is even better. Here are two photos which Clodagh took of lichen on the Oregon Maples:

 Lichen fig1

In the top photo you can see the filament structure of the fungus. The small circular shapes in the bottom photo may be cells of the algae.

Lichens are great survivors. You find them all over the planet in many different environments. And it turns out that they can even survive in space! The European Space Agency arranged to take some lichen up to the International Space Station where they brought them outside, exposing them to the ultra-cold vacuum of open space, where they would be bombarded by cosmic rays and everything. No space suits for them, but they still survived the trip: http://www.esa.int/Our_Activities/Human_Spaceflight/Lichen_survives_in_space