Lichens are plant-like organisms. Lichens are not a moss or plant, but they are an alga and fungus growing together in the same body in a symbiotic relationship. The alga provides food through photosynthesis and the fungus provides the structure to the lichen. Since lichens photosynthesize like a plant, they are not obtaining nutrition from their host. Lichens can be found on trees, shrubs, rocks, wood structures like arbors and park benches.
There are different species of lichens and they are divided into four primary groups based on their body type. The foliose group is a 2-dimensional type lichen. It has very lobed and leafy appearance. The fruticose group is very 3-dimensional, shrubby, and highly branched. It looks almost like a little shrub. The crustose group is very tightly held to the surface it is growing on and has a scaly appearance. The squamulose group is a mixture between the foliose and crustose group together.
Lichens need three basic things to become established. They need an undisturbed area to become established, enough time, and clean air. The wind can disperse the reproductive structures of lichens for miles. Once blown to a suitable environment like a rock, tree, brick wall, or anything else that isn’t frequently moved and receives ample sunlight, they begin to grow. Lichens prefer surfaces that do not change much over time, which is why we tend to see lichens on slower-growing trees like pecans or oaks instead of faster-growing species like pines.
Many people believe lichens are killing their trees and shrubs. The good news is lichens are not harming plants in any way. Lichens are taking advantage of a spot that receives adequate sunlight. If you find that you have large populations of lichens on trees and shrubs in your landscape and you want to reduce those, improving the health of those trees and shrubs will help to reduce the lichen population. Lichens are more noticeable on stressed trees that are growing slower than normal or have a canopy that is declining. The stress could be due to too much or not enough light or water, improper planting depth, or the tree being attacked by an insect or disease. The lichen is not causing the tree any stress.
There are no chemicals labeled for use on lichens. If lichens are found on a tree where they have never been seen before, investigate possible stress sources to the tree. Correcting the stress is the best way to keep lichens from further developing or return.
For more information on lichens, please visit the Home and Garden Information Center website at hgic.clemson.edu. Email Outen at callenb@clemson.edu.
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