Lichens

by Millie Davenport, Horticulture Extension Agent, Home & Garden Information Center, Clemson University, 2010



Hi, I am Millie Davenport, a horticulture Extension agent with the Clemson University Home & Garden Information Center.

Today we are going to take a look at lichens.

At the Home & Garden Information Center we get lots of calls from people who believe that lichens are killing their trees and shrubs. The good news is that these lichens are not harming their plants in any way. Instead, they are taking advantage of a spot that just happens to receive adequate sunlight.

Now, it is true that lichens are often found growing on ailing plants, which makes it hard to believe that they are not to blame for their decline. But if you take a look at trees growing throughout the forest you will often see that they are found growing on healthy trees in those areas.

Now we take a look at this paperbush shrub, you will see that it has very thin foliage, and that creates an environment where sunlight is going to move into these inner branches. It is an ideal environment for lichens to move in, however it is a sign that this plant is performing poorly and they need to look at the culture and see what needs to be changed to thicken up the foliage on this plant to get the lichens to go away.

Lichens are not parasites and they don’t cause any harm to the trees or shrubs in any way. In fact, when you are out on a nature walk you can find them growing in some unusual places like on stone structures of arbors, wooden areas on arbors, park benches or even on rocks.

Lichens are plant-like organisms. They aren’t a moss and they aren’t a plant. In fact they are actually an alga and a fungus growing together in the same body in a symbiotic relationship. The fungus provides the structure to the lichen and the alga provides the food through photosynthesis.

There are many different species of lichens, and those lichens are divided up into 4 primary groups according to their body type. First we have the foliose group, and the foliose group is a 2- dimensional type lichen. It has a very lobed, leafy appearance to it. And then there is the fruticose group, and the fruticose group is a very 3-dimensional, very shrubby, and highly branched type lichen. It looks like a little shrub. And there is the crustose group. That one is very tightly held to whatever surface it is growing on, whether it is a rock or a tree. And it is kind of scaly in appearance. And then there is the squamulose group, and that one is kind of a mixture between the foliose and crustose group together.

Lichens need 3 basic things to become established. One, they need an undisturbed area to become established. Two, they need enough time. And, three, they need clean air.

If you find that you have large populations of lichens on trees and shrubs in your landscape and you would like to reduce those, certainly by improving the health of those trees and shrubs you are going to help to reduce the lichen population. They will start to go away. In general, trees and shrubs need to make sure they have good drainage, the right amount of sunlight, and proper nutrition.

For information on your specific plant species, you can find growing details, plant by plant, on our website at www.clemson.edu/hgic.

For more information on gardening, landscaping, insect and disease problems on your plants, visit the Home & Garden Information Center web site at www.clemson.edu/hgic.

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