• by Dr. Sarah D. Oktay – Managing Director UMass Boston Nantucket Field Station •
What can live in space and almost anywhere on the planet, is abundant on Nantucket, and was studied religiously by children’s author, Beatrix Potter? If you answered lichens, you are correct! I love lichens, they are simply awesome, and Nantucket is a good place to live if you are a lichen fan. I am often surprised by the number of people who find lichens disturbing or ugly or worrisome. They’ll ask why the trees are covered by them and whether the lichen is hurting the tree. Like many other symbionts and epiphytes (plants that grow on other plant non-parasitically), lichens do not hurt trees or shrubs and in fact, lichens are an indication that we have wonderful air quality here on Nantucket.
Lichens are formed by the mutualistic symbiotic association of a fungus (mycobiont) with a photosynthetic green algae or cyanobacteria (photobiont) or both. They are a composite species living as one organism on a solid substrate. The fungal component of lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. The fungal cells are usually anchored to the substrate with hairlike growths (rhizines) that form the base. The lichen body (thallus) is composed of algal cells living inside a compact mass of fungal tissue. The algae are photosynthetic and provide the fungus with carbohydrate nutrients. The delicate algal cells also gain mechanical protection from hostile climatic conditions by being tightly enveloped in a dense meshwork of fungal filaments. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. As kids we are taught that symbiosis (derived from the Greek words for “living together”) is either a good thing or a very bad thing. Mutualism incorporates the positive abilities of two organisms like the fungus and algae that form lichens. Parasitism is the symbiotic relationship that scares us when we think of alien creatures using humans for host organisms. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component. The algae living within the lichen keep their own name, like many modern marriages.
The taxonomy of lichens was first intensively investigated by the Swedish botanist Erik Acharius (1757-1819), who is sometimes called the “father of lichenology”. Acharius was a student of the famous taxonomist Carolus/Carl Linnaeus. The term lichen winds its way through Latin, then Greek via leichēn or lichēn, from the original leichein which means “to lick”. It was first used in 1657. Scientists who study lichen are known as lichenologists. This specialty is a bit safer than others like volcanologists, although not without some controversy as we’ll soon see.
What exactly lichens were and how they managed to propagate went through many iterations. Heinrich Anton de Bary (1831- 1888) was a German surgeon, botanist, microbiologist, and mycologist who studied fungal systematics and physiology. He is considered a founding father of plant pathology (phytopathology) as well as the founder of modern mycology. His extensive and careful studies of the life history of fungi and contribution to the understanding of algae and higher plants were landmarks of biology. In 1866, de Bary hinted that lichens were “double plants” composed of an algae and a fungus. He later defined this symbiosis as the “living together of parasite and host” in either 1869 or 1879 depending on the source in a work entitled “Die Erscheinung der Symbiose”.
The person who gets the most credit (and most derision from small minded colleagues) with developing the idea of symbiosis in lichens is Simon Schwendener (1829-1919). Schwendener was born and educated in Switzerland, worked as a professorial assistant in Germany and in 1867 took up a professorship at the University of Basel in Switzerland. In September that year he gave a talk to Swiss natural historians in which he outlined his ideas about the fungus-photobiont association for lichens. Schwendener was one of the best microscopists of his time and by 1867 he had been studying lichens for a decade or so. I very much enjoy Schwendener’s description of the relationship: “This master is a fungus, of the class Ascomycetes, a parasite, accustomed to live upon the work of others, its slaves are green Algae, which it has gathered around itself, at any rate, holds on to and forces into service. It invests them as a spider her prey, with a fine meshed web, which gradually is converted into an impregnable integument, but, whilst the spider sucks out her prey and throws it aside when dead, the Fungus stimulates the Algae, found in its net, to more lively activity, in fact, causes them to grow larger and causes thereby a luxuriant growth and the thrifty appearance of the whole colony” (eloquently said and quoted here directly from Chambers’s Encyclopaedia, Dictionary of Universal Knowledge, Volume VI, 1901). Many of his colleagues found this assertion to be poppycock and William Nylander (more about him below) considered Schwendener a fool and pariah and refused to associate with anyone who agreed with him, exhibiting truly sophomoric behavior.
Fortunately other lichenologists started to believe in this dual nature when they amusingly ran into difficulty trying to grow their own lichens until they hit upon the idea of combining algae with spores from a fungus. By then, Schwendeners’ “poppycock” theory was starting to look more substantial. Beatrix Potter had spent years drawing microscope illustrations of lichens and fungi, teaching herself everything that could be found in available literature on the topic and trying unsuccessfully to get recognition as a fungi scholar. She too understood this dual nature of plant and fungus. To complicate matters, many citations on the internet name someone called Bennett (no first name given) as the first person to coin “symbiosis” for biological systems (versus the 1620’s societal community definition) in 1877. In another work about lichens published in 1877 (busy year) the German botanist Albert Bernhard Frank (1839-1900) also used the word symbiosis. So there are perhaps three, maybe four people credited with developing the term symbiosis in regards to biological systems and applying it to lichens. I had no idea an entire PhD thesis would come from a tiny etymological trip on the internet.
Back to our friend, the lichen; lichens are “poikilohydric: which means they are capable of surviving extremely low levels of water content. Lichens belong to an elite group of survivalist organisms termed resurrection species. When lichens are desiccated, they are photosynthetically inactive, but upon rehydration they can perform photosynthesis within seconds. You can actually see them become greener, slowly unfurl and open after a good soaking rain. Look for that the next time you are walking around Stump Pond or on pretty much any trail on Nantucket.
The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the plantlike reindeer moss. There are three major types of lichen — crustose, foliose, and fructicose — each of which has its own shape, structure, and environmental preferences. Intermediate types include leprose and squamulose lichen, among others. Crustose lichens are flat and unlobed, with a close attachment to their substrate, and can be difficult to remove from the rock or tree on which they grow. Foliose lichen are leafier-looking, as their name implies, and are made up of two thin sheets of fungus with algae in the middle. They grow in round lobe formations and are easier to pull off of their substrate, since they attach only by small rootlets. Fructicose, or shrubby lichen, have small round branches made of fungus with algae inside, and an unusual pattern of vertical growth that may look beard-like or resemble a small bush. Other types of lichen include leprose lichen, which form powdery, largely unstructured masses without a smooth surface. Placodioid lichens are lobed or unattached at the edges, and closely attached at the center, making them an intermediate form between crustose and foliose lichens. Another intermediate form, squamulose lichen, has many tiny lobes. Dimorphic lichens have characteristics of both squamulose and fruticose lichens, with small lobes that carry tiny stems or branches. Their colors range from brown to bright orange or yellow to black, green, gray, orange and maroon.
Environmental grouping divides lichens into seven major categories. Several types of lichen grow on plants, and are called epiphytic. This group includes the coricolous lichens, which prefer to grow on tree trunks, as well as the ramicolous lichens, which inhabit twigs. The musicocolous lichens grow on live moss, and the foliicolous lichens prefer evergreen leaves. Both of those types are ephiphytic, but the legnicolous, saxicolous and terricolous lichens, which inhabit wood, stones, and soil respectively, are not epiphytes.
I would love to be able to tell you how many species of lichens have been identified, but no one knows that number. Scientists believe that perhaps as many as 750,000 to 1.5 million fungi and lichen exist. One recent paper listed 100 new species http://fieldmuseum.org/users/thorsten-lumbsch/blog/one-hundred-new-lichen-species-described retrieved May 5th, 2013. They found lichens and fungi on every continent from Antarctica to the Galapagos to the Namibia Desert. The hardiness of lichens can be best illustrated by the fact that they managed to survive under simulated Martian surface conditions for 34 days! The European Space Agency discovered that lichens can survive even unprotected in space. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen, Rhizocarpon geographicum and Xanthoria elegans, were sealed in a capsule and launched on a Russian Soyuz rocket on 31 May 2005. Once in orbit the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation. After 15 days the lichens were brought back to earth and were found to be in full health with no discernible damage from their time in orbit (http://www.esa.int/Our_Activities/Human_Spaceflight/Lichen_survives_in_space; retrieved May 5 2013).
Lichens are bio-indicator species which means they show us when something is wrong with the environment. William (Wilhem) Nylander (1822–1899) was a Finnish botanist and entomologist who taught at the University of Helsinki for a number of years before later moving to Paris, where he lived until his death in 1899. Nylander pioneered the technique of determining the taxonomy of lichens by the use of chemical reagents, such as tinctures of iodine and hypochlorite, still used by lichenologists to this day. Nylander was also the first to realize the effect of atmospheric pollution on the growth of lichens, an important discovery that paved the way for the use of lichens to detect pollution and determine the cleanness of air. Nylander noticed that in areas closer to the industrial parts of Paris, lichens could not be found on rocks or headstones or other areas where he remembered them being before. Why Nylander had such a hatred and lack of acceptance for Schwendener’s ideas we’ll never know
Scientists in Europe (Scotland, Britain, etc.) started documenting in the mid to late 1960s and early 1970’s that lichens were falling prey to acid rain conditions. School kids began projects to show where lichens were in relationship to cities. Sulfur dioxide (SO2) emissions from power plants quickly effected lichens, which are heavily dependent on air quality. Within a few years a zonation index was developed by David Hawksworth and Francis Rose (1970) that ranked the species of lichens that could exist at various levels of pollution. They determined a 10 zone system of lichen dispersal. Lichens cannot shut off their intake of air or move like other organisms, so if they are in an area close to industrial sources, they will die if they are one of the many types that are sensitive to air pollution. They also cannot excrete contaminants so they act as bio accumulators. Removing them and analyzing the amounts of pollutants gives scientists an accurate estimate of how much air pollution has existed in one area. I used the epiphyte plant Spanish Moss (Tillandsia usneoides) which grows on a substrate like a bromeliad but looks very much like the lichen usnea or beard lichen as air collectors across the south to determine the amount of radioactive iodine that had reached the southern U.S. from nuclear power plants further north. Some species of lichen are able to tolerate a fair amount of pollution while other species cannot survive in polluted areas (http://www.air-quality.org.uk/19.php retrieved May 5, 2013). The “Lichens of Ireland” project summarizes the research done on lichens as indicators of acid rain and eutrophication (nitrogen) pollution and gives a thorough list of what lichens exist in polluted versus more pristine environments: http://www.lichens.ie/lichens-as-biomonitors/ retrieved May 5, 2013).
I researched several cemetery and stone cleaning websites to get more information on lichens on headstones. Recently in the Inquirer and Mirror someone wrote with concern over the many types of lichens covering headstones in our cemeteries. It is a common misconception that lichens “eat” stone and scientists have argued for years about their impact of gravestones. Typically lichens tend to shield stones from natural weathering from acidic rain and punishing wind. Lichens are a natural and inevitable colonizer of headstones especially in places like Nantucket with perfect weather for lichens (humid, wet) but with not much in the way of substrate (from http://www.rootsweb.ancestry.com/~ncpendtp/cleanstonescem.htm retrieved May 5, 2013).
Most lichens grow extremely slowly, often less than a millimeter per year, and some lichens are thought to be among the oldest living things on Earth. Lichens with known and extremely slow growth rates, like Rhizocarpon geographicum, (also known as map lichen for its patchy map-like appearance as it slowly spreads on rocks) have been used to estimate the dates of geological events such as the retreat of glaciers and the age of rockslides.
Lichens have been used as dyes and as food for millennia. “Rock lichens have played an important role in the survival of native people and explorers. In addition to providing food for their animals, Indians, Eskimos and Laplanders eat certain lichens. Leafy lichens called rock tripes (Umbilicaria) are boiled in soups and eaten raw. They are also added to salads or deep fried, and are considered a delicacy in Japan. Throughout history, peasants of Persia have avoided mass starvation by eating the abundant crustose rock lichen Lecanora esculenta. This lichen readily becomes detached in small patches and is blown off the rocks by wind, often accumulating in crevices and under shrubs. It is mixed with meal and made into a kind of bread in Turkey and northern Iran. In fact, some biblical scholars think this lichen may have been the “manna” which saved the starving Israelites during their exodus from Egypt” (excerpted from http://www.desertusa.com/magdec97/varnish/lichen.html retrieved May 5th, 2013.
Now you may understand why I like lichens so much. Students and their mentors at the UMass Boston Nantucket Field Station studied them several years ago and hopefully new lichenologists are born every day. After a foggy morning or short rainstorm, try to get out and examine the many types of lichens around the island. Although we don’t have the perfect terrain of the rocks hills of Ireland to support the biodiversity of thousands of species, you’ll find more than enough lichen from the alpine reindeer moss near Altar Rock to the crustose lichens covering headstones on our cemeteries to enjoy. To learn more, go to:
Lichens in the northwest and impacts from pollution: http://www.swcleanair.org/pdf/gorgeatmosphericdeposition.pdf
Lichens: Naturally Scottish: http://www.snh.org.uk/pdfs/publications/naturallyscottish/lichens.pdf