Don't freak out when you see this on plants.

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Now that it's spring and folks are getting out more, they're started to notice things about their plants they'd hadn't paid attention to before. An example is this weird gray, green, or even yellow stuff growing on the trunks and branches of trees and shrubs. "Is this moss" they wonder. "Will it hurt or kill my plants?"

Grumpy's reassuring and 117% guaranteed correct answers: No and no.

What they're seeing is not a moss, but a unique, composite, naturally occurring organism called a lichen. A lichen is composed of algae or cyanobacteria and several kinds of fungi. The algae and bacteria photosynthesize and supply the fungi with food. The fungi provide shelter and physical support (although they have no roots). Lichens are more common on less densely branched trees and shrubs where sunlight easily reaches the wood.

Beaucoup forms and colors of lichen exist. Three common forms are flat and crusty (crustose), leafy and bunchy (foliose), and branched and shrublike, sometimes with tassels hanging down (fruticose). Reindeer moss is a good example of the latter.

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Lichens are harmless to garden plants. Their presence usually indicates good air quality. But because lichens often encrust the wood of stressed or dying plants, people assume that lichens are the cause. No so. The plants are stressed or dying for some other reason. The lose a lot of foliage, which allows more sunlight to reach the wood and lichens take advantage.

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There are endless numbers of things to worry about in the world, but lichens aren't among them. Some provide food for wildlife. All remove carbon dioxide from the air. And they're interesting to look at. So like your lichens. They like you.