I'VE TAKEN A LIKIN' TO LICHENS

One of the most interesting subjects I took in the seventh grade was Geography. More than learning about exotic and foreign locations all over the globe, was an introduction to understanding how climate, physical forces, and the advent of biologic organisms have shaped our planet. I was especially intrigued about how solid rock, once it cooled, could be turned into the earth that I knew, the soil I planted seeds in, which grew the grass I had to mow, or which formed the basis of the playground we spent hours on. Freeze-thaw cycles that could rupture rocks seemed self-evident as did the enormous pressure exerted by roots from plants that had taken seed in cracks of the rocks. But what really seized my imagination was the effect of mysterious organisms called lichens that were able to colonize on bare rock surfaces and through their erosive action, reduce rock surfaces to soil.

It is the pioneering capacity of lichens which begins the laborious and time-consuming task of soil building. Thanks to the erosive effects of wind, temperature extremes, and things which break big rocks down into smaller and smaller rocks- i.e, lichens - we have an environment that can now be a host to an infinite array of other life forms. Where could a tropical forest grow without soil to say nothing of a dazzling array of orchids that grow on the plants of that forest? And where could the enormous quantity of wheat and other grains grow that have fed us since the dawn of civilization and even before? None of these would be possible without soil.

Lichens are the most hardy pioneers you will find growing on the surface of the earth - the searing deserts of the Southwest, the frozen tundra of the far north, the wind-swept balds of the Appalachians at altitudes over 6,000', as well as the mostly barren skerries and reefs of the oceans. Owing to their unique construction and biochemical composition, one can find a lichen almost anywhere where there is fresh water except where man has fouled the environment with air pollution. As tolerant as they are for climatic extremes they are hypersensitive to sulfur dioxide, heavy metal precipitates, and fly ash. They are barometers for the prudent - when you see evidence of dying lichens or worse, no lichens at all, you had better start asking questions. (The lichen above was found out in the Arizona desert, surviving in the extreme aridity and heat.)

From the strictly utilitarian point of view, a whole culture of northern people, the Inuits, have often subsisted on eating lichens and indeed lichens have helped many survive such inhospitable climes in times of isolation, and without them, many an unlucky explorer, e.g., Scott, Lord Franklin, etc., did not. The whole food chain of the northern tundra depends on lichens for they serve as the basic food for caribou and reindeer. Various cultures around the world have used lichens as part of their diet as have a variety of rodents, herptiles, and insects.

Something vastly intriguing about lichens has to do with their cellular composition. Although they are given genus and species names, are recognized by their individual, constant morphology, have reproductive structures, etc., i.e., all the usual things characteristic of any living organism, they are the unique product of two vastly different biologic entities, a fungus and an alga! The fungus provides minerals, protection, and a fixed place in the environment while the alga provides oxygen, sugars, and other necessities of life. Quite a marriage, actually! You can separate the fungal and algal partners and grow each separately in the lab and, here is one of the great phantasmagoric happenings in biology, when you put them back together they do not grow as two separate entities, but rather they morph back into the habit of the lichen species from which they originally came! Some see this partnership as mutual symbiosis and others see it as parasitism, i.e., the fungus is parasitizing the alga. If that it parasitism, it has no other parallel in all of nature.

In addition to providing a soil-manufacturing mechanism and a food source, lichens also serve to colonize formerly barren wastelands, i.e., they are often the first pioneers in what will become a steady, but changing succession of flora. I live near a former artificial lake that had been drained when the dam(n) structures decayed past usefulness. This left a largely barren, clay base on which hardly anything grew. Among the hardy pioneers of Brookside Alder and "Poverty Grass" were of course lichens. Not only do the lichens help stabilize the soil from wind erosion, some species have the capacity to fix or add nitrogen back into the soil, thanks to the blue-green algae present in some species.

There are four major lichen types as well as a few lesser oddballs (isn't that always the case?). Those that are leafy and easily detached from the bark, soil, rocks, or whatever they are growing on are called Foliose lichens. The illustration at left is an example that is found growing on trees throughout most of the eastern U.S. and southern Canada. It is the Green Shield Lichen. Its characteristic yellow-green color and rosette shape is found commonly growing on tree bark. It is very sensitive to air pollution.

A very interesting group is the Fruticose lichens which consist of those that are tufted, pendant, or shrubby and consist of many branches, often with extremely fanciful fruiting bodies grossly visible. A good example of "fanciful" is the one pictured at the top, the Common Pixie Cup Lichen. The lichen at left is one of the most easily recognized of all lichens. It is called "British Soldiers" in references to the colorful red fruiting bodies' resemblance to the British Redcoats of colonial times. The most interesting thing about this lichen is that it does not grow in Britain! Love it.

A smaller, but very interesting group is the Umbilicate lichens, so called because they are attached to their substrate by a small (compared to their large size) holdfast or belly-button. Many are very easily recognized and are found in very shaded, moist locations. Some species were especially prized by pioneer women who extracted colorful dyes from their substance to dye home-spun fibers, like the one at left, Rock Tripe.



The hardest group to work with is the Crustose lichens because they can not easily be removed from what they are growing on; you need a geologist's hammer to break off pieces of rock or what not and Rangers and Park Superintendents take a dim view of me taking a chip off of some historic monument :). Also, the identification requires more technical skill, more microscopy, and even biochemical testing. Nevertheless, they are intriguing and worth the effort. The specimen at left is an easily recognized Concentric Boulder Lichen.

Thanks to some time on my hands, the hankering to explore wild places, and the availability of some first class resources to help me, I have been endeavoring lately to learn the names of some of these fantastic organisms in my midst. Somewhat daunting is the need to acquaint myself with a lexicon of technical terms like isidia, soredia, squamules, podetia, etc. Also, it is extremely useful to acquire a dissecting microscope, that is one that provides clear enlargement 5-20 X. I have no excuse now, I've got to get busy - there are an estimated 3600 North American species of lichens north of Mexico. Speaking of excuses, please excuse me, I have some specimens collected yesterday in a wild outing I must now examine.