Want to get children outdoors to look for a life form that doesn’t bite, sting, or pinch, and that they are sure to find? At a recent family reunion in northern Alabama, every child brought back a sample. Most were gray or green. Some were yellow, red, or orange. Some were on dead tree limbs, others on rocks, and one was found on the wall of a building.
Wrest children away from cell phones and computer games and they quickly learn to appreciate nature in all its myriad forms. The organism in question is one that any child can find – in the backyard, at a park, or on an old brick. I never get tired of my grandchildren saying “look at the lichens I found.”
What exactly is lichen (pronounced lie-ken)? Although they look like a single organism, lichens actually represent a complex relationship between fungi and algae. The species live together in a permanent symbiotic partnership in which each provides for the other, contributing to their joint survival in special and essential ways. Like higher green plants, algae convert sunlight into usable energy through photosynthesis, a process fungi cannot perform. Fungi are able to absorb vital nutrients from the surface they grow on. Hence, algae provide energy; fungi supply minerals. Ultimately, both species benefit, resulting in a single living organism that is far more complex than its superficial appearance reveals.
Lichens are easy to find. Oaks and other hardwoods have patches of greenish gray lichens that may be spongy or flat and dry. Lichens are everywhere! Pick up a dead limb and you will find lichens. Next time you see what appears to be a bare cliff face or rock wall, take a closer look. You will find lichens anchored into the rock itself. More than 17,000 species of lichens have been described, most belonging to the fungus group that includes the edible morel mushrooms.
Lichens occupy a variety of habitats worldwide. What might seem to be a fragile life form may actually be one of the toughest organisms around. I remember being impressed by an entire mat of lichens covering a rock wall in the Mojave Desert where temperatures were well above 100 degrees F. Reindeer moss is a type of lichen eaten by caribou in arctic regions. The lichen carpet in some regions of tundra provides the major source of food and nutrients for the big herbivores, which in turn are a primary food source for wolves. Ironically, an awesome predator ultimately depends on a food chain that begins with a combination of fungi and algae.
Unfortunately, the otherwise durable lichens are believed to be highly sensitive to some components of modern air pollution. They have been reported to be intolerant of toxic materials such as sulfur dioxide, heavy metals, and fluorine. Lichens have been proposed for use as ecological indicators in areas with high air pollution from industrial sources. One report noted a gradual increase in lichen abundance from the center to the outskirts of an industrial area.
Lichens serve as a food source for many animals, besides caribou, including moths, slugs, flying squirrels and mites. Hummingbirds, vireos and other birds use lichens for nest material. Lichens are even used by humans for dyes, antibiotic salves and perfumes. Litmus paper, which can determine the acidity of a liquid, is made from a species of lichen. And the alpine reindeer lichen is used to make tiny little trees for model railroad displays.
Most of us pay no attention to lichens, yet they are an important and fascinating part of the living world in our yards, local parks, and woods. Look for the pale greenish or gray coating, sometimes in little patches, on tree trunks, large rock faces, or on the soil itself. These two completely different, little-noted life forms can live in harmony together to make another that is remarkably persistent and pervasive. This is a natural wonder as fascinating as any you might see on television. And it’s right outside your door. That’s another thing I’m trying to teach my grandkids.
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Whit Gibbons is an ecologist and environmental educator with the University of Georgia’s Savannah River Ecology Laboratory.