Friday, May 20, 2011

A Little about Lichens

If you’ve ever roamed in the woods in our area, you have likely run across lichens.  Lichens are interesting creatures . . . they are a hybrid, symbiotic organism that is composed of fungal tissue and blue-green or green algae.  The algae’s job is to make food (in the form of sugar), which the fungal tissue can feed on while the fungal body provides water, other nutrients, and physical protection to the algae. 

Lichens can be found on tree bark, branches, rocks, old fence posts, soil, and other structures they find suitable for growth.  They are found in almost every environment on earth:  deserts, tundra, rainforests, mountains, and coastal shores.  They need light in order to grow and photosynthesize, so you won’t generally find them growing in areas with deep, heavy shade. 

There are three main growth forms of lichens that grow on trees and branches:  fruticose, foliose and crustose.  Crustose forms are usually flat and crusty, foliose growth resembles “leaves” and fruticose has a more “shrubby” appearance.  Lichens grow incredibly slow -- usually just a few millimeters a year.  On rocky outcrops in our area, even a small child’s footprint on a mound of lichen can take decades to grow back, so it’s important to tread lightly in sensitive areas where lichens grow. 

Because lichen have no leaves, stems or roots, they must absorb water and nutrients from rainfall and the nutrients in our atmosphere.  Some types of lichen will not grow in heavily polluted areas; thus they are important air quality indicators.

There is a common misconception that lichens cause plant damage.  Many homeowners fear that a heavy lichen layer on tree or shrub branches is problematic and harmful to the plant.  Not so.  It is likely that some other plant stress is occurring (poor growth, lack of nutrition, insect or disease pressure) that leads to a decrease in leaf coverage.  This decrease in leaf growth allows more light into the canopy of the plant, reaching the branches and limbs, and lichen can take advantage of this increased light and set up camp. 

So fear not . . . lichen is a benign organism that does not attack or kill plants.  If you take the time to actually look at lichens up close, taking in the variety of colors and textures they offer, you just might begin to appreciate their visual beauty!

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