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What Is This Alien Stuff On My Plants' Bark

Eddie Powell
Horticulture Extension Agent
Walton County
732 North 9th Street
Defuniak Springs, Fl   32433
pep5@ufl.edu
850-892-8172
850-892-8443

Throughout the year I get many calls asking "what is this mossy-like stuff growing on my landscape plant's bark?" For the most part the calls are in the spring time when people have come out of hibernation from the winter and see their landscape plants covered with alien-looking growth. Well I am here to say it is not alien, though it may look like it is. These are lichens.

Lichens on Bradford pear tree bark Photo Credits: Eddie Powell

Lichens often get mistaken for some unusual fungus that is killing their trees. However lichens are not single organisms, but rather a combination of two organisms that live together in a beneficial way. There are over 20,000 different types of lichens found in nature. Lichens consist of a fungus and cannot survive on its own; therefore, the fungus is more dependent upon its algae partner which produces enough food for both to survive. Lichens are also very different from plants because they can survive a complete loss of water. During this time, brittle pieces that flake off can later grow into new lichens. When moisture becomes available again, the lichen absorbs water and returns to their fleshy form. So with this stated, the lichens growing on trees and shrubs are not parasites and do not harm the plants in any way. Lichens use plants as support structures to become established.

There are four different forms of lichens found, crustose (crust-like, growing tight against the substrate), squamulose (tightly clustered and slightly flattened pebble-like units), foliose (leaf like, with flat sheets of tissue not tightly bound), and fruticose (free-standing branching tubes). Colors range from white to gray, green, red, yellow, and black. Lichens commonly found in our area are in the crustose, foliose, or fruticose form, and are white, gray, or gray-green in color.

Because lichens produce chemicals, they have very few natural predators. However, the most serious threat to lichens is air pollution. Most lichens will not grow in a polluted atmosphere and therefore you should be glad to see lichen here or there in your yard, as this is an indication that the air is relatively clean.