|Lichen and moss|
Common Lichen Growth Forms
There are over 15,000 species of lichen worldwide and 1000 in the Pacific Northwest, so learning to identify them may seem like a daunting challenge. A more realistic approach might be to distinguish these common growth forms:
Crustose – A crust on a rock or other surface.
|Fruticose – A tuft of tiny, leafless branches.|
|Foliose – Flat leaf-like structures.|
|Leprose – Looks like a powder.|
As I was reading about lichens, it seemed to me that there is a basic problem with the classification of lichen species, even when it is a single fungus and alga living together. A lichen isn’t a single species. It is at least two species living together. Taxonomists have had neat little species boxes that they put all living things into, but, as it turns out, lichens don't fit in these boxes. It looks like we need a different way to classify lichens. Further reading revealed that by convention, lichens are classified as species using the species name of the fungus. However, this is not without problems. A fungus may pair with different algae, and the results can produce quite distinctive forms that would merit classification as different species. Furthermore, some lichens include two species of fungus. Oops! It appears that we need a different kind of box for lichen classification. This is a hot topic among lichenologists.
All this diversity of different fungi and algae living together is what makes lichens particularly hardy, enabling them to populate the entire planet, living where nothing else can, surviving icy cold mountains and hot, dry deserts. They are sometimes the only living thing that can survive in these extreme environments. They are often the first living things to grow after a disaster has destroyed other life forms.
Given a place to grow, sunlight, and water, lichens seemingly live independently in their own little world. However, they play many important roles in the larger ecosystems where they live. Some lichens are an important food source for animals, for example, reindeer. Northern flying squirrels eat lichen in winter and use it as a nesting material. Hummingbirds also use lichen in their nests. In the distant past, lichen has been an important human food in both Europe and North America.
I'm often asked whether or not lichen growing on trees harms the trees. I wasn't sure but I thought that it didn't. Understanding how lichens function in the ecosystem enables us to give a more definitive answer to that question. Lichens do not have roots. They are not parasitic like mistletoe, and do not rob nutrients from their host tree.
|Lettuce Lichen (BLM photo)|
Finally, another fascinating characteristic of lichens: Since they get their nourishment from the air, they also absorb any pollutants in the air. Some lichen species are sensitive to air pollutants and will be damaged or even die if air pollution levels are too high. It is possible to determine air quality by looking for the presence and at the quality of these sensitive species. Scientists also gather lichen and moss samples and use them to measure air pollutants. This is how they recently discovered high levels of cadmium and arsenic in the air near two artistic glass factories in Portland.
A Field Guide to the Lichen of Opal Creek
How a Guy From a Montana Trailer Park Overturned 150 Years of Biology
How Tree Moss Could Revolutionize What We Know About Air Pollution
The Hidden Forest by Jon Luoma, Oregon State University Press, Corvallis, OR