Window On Nature
By Lowell & Kaye Christie, F47246
Although you might not know it, you probably have seen lichens somewhere in nature. Right now some are growing atop a granite rock in our front yard. Once you know what these interesting organisms are, you shouldn’t have any problem spotting them on a tree or a rock at the next campground you visit.
Lichens have an unusual genealogy. Two completely different organisms, a fungus and an alga, are brought together by chance and work cooperatively to produce lichens. Because of its diverse parentage, the resulting offspring is neither plant nor animal. The alga’s job is to use photosynthesis to produce food for both partners. The much larger fungus bears the responsibility for building the lichen body (thallus) that houses and protects both the algae and fungus. This teamwork must work well, since lichens are found worldwide.
Lichens are divided into four basic growth forms: crustose, foliose, fruticose, and squamulose.
Crustose lichens are flaky or crustlike and lie flat. You’ll delight in spotting bright red, yellow, or green splashes across rocks, soil, or bark.
Foliose (leaflike) lichens can be papery thin or, in more advanced forms, netted and branchlike. Branched foliose lichens have a distinct top and bottom surface, a quality that easily differentiates them from most other lichens.
Fruticose lichens are the most highly developed of the clan. Their branches are much closer in form to true branches of plants. The British soldier lichen is one of the showiest fruiting lichens: When you first spot a patch in a forest, they look like tiny, red-topped toothpicks. But you’re more likely to spot a lichen known as old man’s beard. Look up “” you may see this grayish-green mass hanging from a tree.
Squamulose lichens have scalelike lobes that are typically small and overlapping.
The likelihood of seeing lichens as you travel (unless you go directly from one city to another without getting out of your motorhome) is nearly 100 percent. Scientists have cataloged approximately 3,600 lichen species in North America, and more than 500 different species have been found in Wisconsin alone.
Lichens don’t demand rigid growing conditions to survive. They’ll latch onto rock, soil, or trees. You can expect the greatest number of species to be found in temperate climates, but it’s not unusual for them to grow in arctic locations. Lichens are especially noticeable living on the tundra. They and the other ground-clinging species, such as liverworts and mosses, provide insulation to the ground and forage for animals. In some places they are plentiful enough to be actively sought out by reindeer and other arctic grazers. Caribou actually dig craters in the snow to expose lichens that they first detect by smell. These mammals must be good at it; over the winter, lichens form 90 percent of a caribou’s diet.
Other lichens grow in extremely arid deserts, even in areas with constantly shifting sands. Their very presence helps provide a living crust to the sand. And finally, if you know where to look, you can locate a few lichen species specially adapted to the tropics, living in bayous and in cool rainforests “” just so they aren’t in standing water.
Humans also have benefited from lichens. Some lichens are edible, but don’t rush out to harvest them, as a few species are poisonous. Researchers also have found other uses for lichens, such as in antibiotics, perfumes, and deodorants.
Several American Indian tribes use lichens to produce dyes for wool. Depending upon the lichen species and the process used, they can end up with fleece of gold, brown, magenta, and other hues. But those who use lichens must be careful not to overharvest. At a typical growth rate of approximately a millimeter a year, it takes a long time for a lichen to return to its former size.
Lichen reproduction is tricky. One method is for the fungus part of the lichen to reproduce on its own, creating tiny spores that are carried away by the breeze. On a good day, some of the spores float down on appropriate algae. Other lichen species mingle their genes at home and rely on a passing creature to brush off some of the tissue and deposit it down the line.
Lichens growing in sand have no real grip on the surface. In this case, tiny pieces of them are spread by anything that moves “” wind, water, or creatures. Finally, there is local wear and tear on the lichen. Tiny pieces break off and are dispersed just enough to ever so slowly increase the overall size of the patch.
In spite of their seeming fragility, lichens are believed to be among the oldest living things on Earth. So far, experts have positively identified lichen fossils dating back 400 million years. Some researchers insist that far older lichen samples exist, but given the difficulty of reaching agreement on what constitutes a “real” lichen fossil, consensus may never be reached.
By the mid-1800s, botanists had noticed that lichens were becoming rare in and around large towns and cities. After doing some research, they recognized that air pollution was affecting lichen colonization and growth. Once they identified which species are most sensitive to air pollution, by documenting the lichen presence or absence, they were able to determine how “clean” or “dirty” the air was in a particular area.
You can use this knowledge to determine the air quality in your area. Examine a few older trees. If you notice scattered patches of gray or orange lichens growing on the bark, take a deep breath. Where lichens thrive, you know the air must be pretty healthy. But should you find yourself in an area with a lot of spindly or dead lichens, keep going. The air quality there is more than likely poor. Nobody wants to camp in a “lichen desert.” But there is hope that as the air quality in such places improves, lichens will reappear.