They’re likely lichens, and they’re not harmful
It’s spring, and you’re out in your garden enjoying the flowers and making plans — and then you begin noticing problems.
When you glance at a nearby tree, you may see patches all over the trunk, bark and stems. These patches, or spots, are commonly white or green, but sometimes they are gray, pink, red, yellow or lime green. They may appear crusty, shrubby or leafy.
(Courtesy of Nicole Pinson)
Although they look like some type of harmful organism, they are, in reality, harmless lichens, pronounced lī-kens.
Lichens are not plants. They do not have a vascular or circulatory system that moves water and nutrients. They do not have roots, stems or flowers, either.
Actually, lichens are made up of two organisms that live together: an alga and a fungus. The lichen relationship is unique. The alga makes food for the lichen through photosynthesis, but it cannot live on its own.
The fungus provides protection and helps anchor the alga. The fungus also prevents the alga from being damaged by too much light.
Lichens are able to live in diverse, even difficult, places. You can find lichens attached to rocks, cliffs, tree bark, bare soil, fence posts, concrete walls and gravestones.
Since they lack a vascular system, lichens get their nourishment from rain, fog, dew and moisture released by plants and debris.
Lichens do not parasitize or harm the structures or plants they are living on. The common “deer moss” found on bare soil in natural areas, such as in state and county parks, is actually a lichen.
Lichens grow slowly, only a few millimeters per year, and they can live for thousands of years. Because of their long life spans, scientists measure lichens and use this information to date rocks and events.
Lichens provide many benefits. They are a food source for animals. They provide protective camouflage. They are useful in tanning and dyeing cloth. In some parts of the world, they feed large herds of caribou. Lichens supply nesting material for birds and mammals. In some cultures, lichens are used for medicine and as a minor food source.
As they grow over bare rock, they help collect organic matter, which builds and replenishes the soil over time. Lichens are also associated with good air quality. Lichens reproduce asexually, most often when pieces break off and start new lichens. Or, they reproduce sexually through spores. Because pollution can affect their growth and reproduction, lichens may not grow in highly polluted environments. For this reason, they are at the center of worldwide research studying the relationship between lichens and air pollution.
Although lichens are often mistaken as disease or fungus, they are harmless.
As we always say in Florida Friendly LandscapingTM and pest management, identify the “pest” first before selecting controls.
If your tree appears stressed or unhealthy, consider other factors such as planting depth, drought, disease, insects or water. And if you see a lichen, remember you don’t need to do anything to “treat” it.
For additional information, contact or (813) 744-5519, Ext. 54145.
Nicole Pinson is an Urban Horticulture Agent in Hillsborough County.
This column used information from “Lichens” by Gary H. Brinen of Alachua County Extension, http://alachua.ifas.ufl.edu/lawn_and_garden/fact_sheets/lichens.shtml.
Published April 22, 2015
