Recently I’ve heard some complaints about frilly looking, pale green fungus killing people’s trees. It seems like I hear more about them this time of year and I’m guessing it’s because there are no leaves on the trees, making the lichens more noticable. Lichens tend to get a bad rap because they look like something that shouldn’t be there.
Lichens are made up of two different types of organisms: fungi and algae or cyanobacteria. The fungi and the algae form a symbiotic relationship where the algae, or photobiont, photosynthesizes to produce food for the fungi, also called the mycobiont. In return, the fungi provide protection from the elements for the cyanobacteria. Since the photobiont part can photosynthesize just like a plant, lichens do not need to obtain their nutrition from other plants. This sets lichens apart from plant parasites like mistletoe, which need a living host to obtain nourishment.
To simplify the last few sentences: Lichens do not harm the host they grow on.
The photo below shows two different forms of lichens. On the left is a fruticose form and on the right is a foliose form
Reproductive structures of lichens can be disseminated by the wind. We tend to see lichens more often on slower growing tree species like oaks or pecans as opposed to the faster growing species like pines. This is because lichens prefer a surface which does not change much over time. Sometimes lichens are more noticeable on stressed trees because the tree may be growing slower than normal. The cause of the stress could be from receiving too much or not enough light or water, improper planting depth, or the tree is being attacked by an insect or disease. Again, the lichen itself is not causing the tree any stress. Something else may be going on.
Here is a little fun fact about lichens: They are very sensitive to poor air quality, so if you see lichens growing on trees around your property, it’s a pretty good indicator that you’re breathing clean air.