Lichens: They are not a disease killing your trees

By Pam Baytos

OSU Extension Master Gardener Volunteer

Did you hear the story of a fungus meeting algae; they took a “lichen” to each other (insert groan).

Although this is amusing to some, the concept of a lichen is misunderstood. Their presence on your tree is not a problem – it’s a good thing.

Lichens are a unique organism because they are actually a symbiotic (mutually beneficial) relationship between two organisms: fungus and algae.

The fungus grows on the tree and can collect moisture, which the algae needs. The algae, in return, can create food from the energy of the sun, which feeds the fungus.

As the lichens produce their own food, this means they do not feed on the tree bark.

Lichens grow on anything that sits still long enough, including tree trunks, rocks, fence posts, tombstones, to name a few.

Lichens on tree bark are completely harmless to the tree itself. The rhizones (similar to roots) allow them to attach to the tree but do not go deep enough into the inner bark to harm the tree in any way.

Unlike plants, lichens do not have leaves, stems, roots or a waxy outer cuticle to control body water content.

Lichens continue to grow during periods when dew, mist and rainwater are present, but a summer dry period can cause them to become dormant until the next rainfall.

Lichens grow in many interesting forms. Those with flattened and crusty appearance are called crustose lichens. Foliose lichens have raised, leaflike lobes.

If you look closely at this type, it’s like nature’s way of putting snowflakelike decorations on your tree.

Fruticose lichens have branched growths with finger or threadlike projections. Colors range from gray-green to bright orange-red.

Lichens reproduce when small pieces containing both organisms break away. These fragments can be carried by wind or water to a new location.

Lichens provide many benefits, both in nature and human culture.

Lichens are eaten by many animals such as deer, mountain goats and caribou.

Many species of birds use lichen material in constructing their nests.

Certain lichens are used in producing antibiotics, while others provide the miniature plant landscaping for model railroad tracks.

No management is necessary or should be done to reduce the presence of lichens or your trees or any other structure in your landscape.

In fact, finding lichens on a tree in your yard is a sign that the air surrounding your tree must be pure since lichens will not grow in areas with smoky or polluted environment. This is why lichens are still misunderstood in the Mahoning Valley.

Many people believe when a tree becomes sick and has lichens, that the tree lichens are the cause of the illness. This is impossible. Most likely, the lichens were there long before the tree became ill.

To learn more about lichens, visit go.osu.edu/lichens.