Some of the most unusual, ancient creatures on earth are living in your garden, happily weathering the worst weather thrown their way. Some gardeners see them as monsters, which is sorta the truth.

The plant-like organisms are called lichens, and each is actually a unique Frankenstein-like mashup of algae and fungi. In this strange symbiotic relationship, the fungi protect and anchor the algae, which in turn convert sunlight and atmospheric nitrogen into carbohydrate food for the fungi.

These rootless composites, which have proven to be able to survive being exposed unprotected for weeks in outer space, thrive nearly everywhere on earth, from tropical rainforests to above the tree line in alpine mountains, across arctic tundra, and on volcanic rock and even slag heaps outside metal processing plants. Some are among the oldest living organisms on earth, with one colony estimated to be over 8,000 years old.

Lichens (pronounced “like-ns”) grow in a wide range of sizes and forms, from powdery to flat crusty mats that look like peeling paint, to curly gills and tiny frilly growths that are sometimes used in model railroad scenes as miniature trees and shrubs. Their colors range from dull gray, blue, green, red, orange, or yellow, with their brilliance perking up after a rain. They’re what lend spectacular displays to rocky faces of mountains and desert trees. Some of my favorite aesthetic photos are of lichens I’ve found crusted on centuries-old tombstones.

They’ve been used in medicine and art, and as strong indicators of heavy metal pollutants. Best of all, they are sustenance for wildlife – they are the main winter forage of caribou. Reindeer food.

Here’s the rub: I get lots of emails and calls from gardeners who find lichens on old tree trunks and limbs of usually ailing old shrubs and think they’re a plant-killing disease. They’re not.

What they are, is a symptom of a plant not growing very well. As it grows, a healthy plant shucks the lichens off before they get too established; however, when a plant is weak or unthrifty from diseases, damage caused by bad weather, root or trunk wounds, or just old and in decline, lichens can completely envelope branches.

But the self-contained ecosystems adhere only lightly to bark, without causing harm; even on rocks they only cause a gradual weathering of surfaces. You can actually peel lichens off and see there is no damage whatsoever underneath. Other words, they are not parasites like shrub-like mistletoe with roots growing into tree limbs, or the very odd masses of orange spaghetti-like dodder vine that clambers over and sucks its nutrients from the host plants; lichens are more like epiphytes such as hanging Spanish moss and those small fern colonies that grow atop but not into old tree limbs.

By the way, I converted a shade-cooled area of my back garden with a splashy water into a “stumpery” – a jumble of old mushroom-encrusted tree stumps, dwarf palmetto, and mosses and other shade perennials. To create a memorable Old South pastiche, I propped up the branchy trunk of a dead cypress tree and draped it with Spanish moss; it took a while but now I have some very interesting patches of lichens forming on the twigs.

Look around at your older shrubs and trees. If you find lots of lichens, the thing to do is prune hard or at least thin out some of the cluttered growth this winter or next spring to stimulate strong new shoots, and fertilize in late spring to support that growth.

And ignore – or better yet, admire and celebrate – the ancient lichens.

Felder Rushing is a Mississippi author, columnist, and host of the “Gestalt Gardener” on MPB Think Radio. Email gardening questions to rushingfelder@yahoo.com.

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