Lichens: A lesson on how to get along

They’re delicate, but tough; beautiful, yet crusty. They’re also found almost everywhere, but you probably don’t pay them much attention.

They grow in patches on rocks, trees, buildings and just about every other surface. They’re under-researched and misunderstood. Most people probably don’t even know their name, which is lichen, by the way.

I’ve written about lichens before (after a trip to Seattle, where they are prolific). I decided to write about them again because I’ve been getting lots of questions about them lately. Plus, there’s some interesting new research that changes even the most basic understanding of them.

Usually, when I get questions about them, people ask me about “that crusty green stuff” growing on their tree or shrub. They are often worried the crusty stuff is damaging their tree or shrub.

That actually isn’t the case. Lichens don’t typically cause damage to trees — they don’t need to. Their presence is usually normal, even on trees and shrubs.

You’ll likely see more on older plants. If they are appearing in larger numbers on newer trees or shrubs or you see complete coverage of older plants, it is likely an indication that the tree or shrub is not as healthy as it could be. They’ll also be more prevalent in wet or moist areas, such as deep woods or near streams.

If you see lots of lichens on trees or shrubs, especially young ones, you’ll want to think about what could be causing the plant to decline. It could be planted in the wrong place (too wet, too shady, etc.), have disease or insect issues, or fertility issues. Check for other signs and treat accordingly.

Lichens are interesting in that they aren’t a single organism. For many decades, we believed they were a combination of two organisms — a fungus and an algae (or a cyanobacteria, sometimes incorrectly called blue-green algae).

Recent research published in the journal Science shows that many lichens actually consist of a third partner: another fungus called a basidiomycete (or, as you know it, yeast). So many of these organisms are really three organisms, all living as one — a lichen-a-trois, if you will.

In most cases, these organisms cannot live apart from each other. You won’t find just the fungus or algae or yeast living on its own. They form a symbiotic relationship, each dependent on the other while providing something in return.

The fungus forms the basis of the structure. It is so much a part of the structure of the lichen that they are classified and identified mainly by the fungus.

The algae forms a thin layer on the surface, protected by the fungi while it harvests sunlight to produce sugars to feed the fungi. And because these organisms live out in the elements, they often contain numerous other bacteria, fungi and microorganisms — much like our digestive system contains a large number of microorganisms.

They are even home to one of the world’s most popular microscopic creatures — the tardigrade (or water bear), which is the world’s smallest animal (if you don’t know what a tardigrade is, you should definitely look it up).

I’ve seen lots of information on lichens lately, from new research to articles talking about them all over social media. I listened to a fascinating podcast and blog called “In Defense of Plants” about lichen conservation featuring Jessica Allen, a Ph.D. student at New York Botanic Garden and the City University of New York.

There’s still lots we don’t know about these fascinating organisms, and research like hers is responsible for greatly understanding the organisms and their importance.

According to Allen, the biggest threats to these interesting organisms are air quality and climate change. While they are tough and can live in many different extreme climates, clean air is a must for their survival.

As we expand the cities where we live and produce more atmospheric pollution, the range of lichens shrinks. You’ll find far more in the woods than you will in the city. Increases in temperatures are also responsible for a decrease in lichen diversity.

While you may not think lichens are important, their presence is important — from soil conservation to helping erode rocks and serving as pioneer species for newly developing habitat. So it is important to preserve our lichen population.

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