Last Tuesday I sat in the examination room waiting for my annual physical exam to commence, shivering in my skivvies and trying to shake off the memory of an old New Yorker cartoon, the one with the patient sitting on the exam table facing the doctor and saying, “You’re going to keep looking until you find something wrong, aren’t you?” Something like that.
I had been worrying about a couple of molelike growths, one at my left temple and the other at the base of my throat, that seemed to be slowly enlarging and turning darker. Their existence was bothering me more than the cranky knee, the aching shoulder and the acid reflux that has increased exponentially since freshman physics took over both ends of every teaching day.
Imagine my relief when the doctor pronounced these moles to be harmless, giving them a long technical name, and my delight when he added, “They’re like lichens on a tree.”
This is as it should be, I thought. I’m aging like an old tree, taking on passengers in the process.
What are lichens? In the strictest sense, they are not plants at all, but two organisms — a fungus and algae — living intimately together in a symbiotic relationship. As one of my students eloquently described this arrangement, “the photosynthetic algae provides the food, the fungus provides a place to hang out.”
I’ve developed a fondness for lichens since moving to Maine. The gray-green lichen called Old Man’s Beard that hangs in long tresses from the branches of coastal spruces reminds me of Spanish moss, an epiphyte related to pineapples that festoons the knobby horizontal branches of old live oaks growing in Charleston, S.C., an old stomping ground.
Of late I have noticed clumps of lichens attached to slender, snow-covered hardwood branches. These lichens are green, apparently photosynthesizing at below-freezing temperatures, while the tree sleeps.
I spend winter hours exploring granite surfaces exposed by the sun’s warmth, constantly amazed at the diversity of lichens growing there: crusty lichens that cover sections of the rock in intricate patterns of gray, green and orange; colonies of brown, leafy lichens that trail down the sides of the rock; pillowlike masses of silver-gray lichens that branch like miniature shrubs. All seemingly active and growing, despite the cold.
Lichens also grow on the trunks and branches of trees, and often I am asked if the lichens harm the tree, if they are parasitic or if they mark a diseased or dying tree, all misconceptions arising from the abundance of lichens on dead branches or declining trees. In fact, lichens increase their growth rate in full sunlight and thus are more abundant where lack of foliage admits more light. They do the tree no harm.
The presence of some lichens in the garden, whether growing on trees or rocks, is an indicator of pollution-free, moist air. The shrubby and leafy lichens are the “canaries in the coal mine” — they will not grow where the air is polluted — while the crusty lichens, the ones that cover the surface of rocks and pavement, are more tolerant of sulfur dioxide and other pollutants. Old Man’s Beard is a reliable indicator of a pollution-free garden. The crusty lichens that cover the surface of granite boulders are pioneers in soil genesis, secreting organic acids that weather the surface of the granite, eventually forming a pocket of mineral soil deep enough for a grass plant to grow. All the while, moisture trapped by the lichen at the surface of the rock cycles through freezes and thaws, slowly expanding tiny cracks in the rock, making way for the roots of a tree or shrub seedling. It is part of the education of a gardener to sit atop a granite outcrop and survey these various stages of soil formation.
Lichens hang out on rocks or the old headstones in the cemetery. And they hang from the branches of trees. They are remarkably tough, enduring exposure to freezing temperatures in winter and extreme desiccation during summer droughts. The gardener cannot cultivate lichens, only make room for them. They are an important part of the rock garden and xeriscaping (techniques to conserve water in your yard and garden) because they are not dependent on a constant supply of moisture. Their ability to survive alternating periods of drought and abundant moisture give them an advantage in colonizing stressful environments. Wherever lichens appear in the garden, on rocks, garden benches or in trees, they should be embraced as signs of a healthy environment, of a garden in tune with nature.
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