“There is a low mist in the woods—It is a good day to study lichens.”
Henry David Thoreau, A Year in Thoreau's Journal: 1851
I have often thought of Henry David Thoreau as a like-minded soul when I read one of his essays. From his desire to 'saunter' though the woods of Concord, MA, to his thirst for solitary moments and his love of good company, he and I have a lot in common. According to his journals, Henry David spent some portion of his time in the woods observing and studying lichen.
You can’t walk ten steps from your front door without seeing lichens. It matters not whether you live in a city, a suburb, or in the woods. The problem is that you might not notice them, or you might not realize what you’re seeing. My relationship with lichens was slow to develop, but they are now a keen interest of mine. The more time I spent walking in the woods, or even in my neighborhood, the more I come to know and appreciate their tenacity and their beauty.
What are lichens really? They are a remarkable close association, scientist call it a symbiosis, of organisms from two, or three, of the six Kingdoms of Life. The photobiont of a lichen- the organism that captures light energy during photosynthesis to make sugars – is an alga from the Kingdom Protista (giving some lichen a green color) or a cyanobacteria, imparting a darker hue, from the Kingdom Eubacteria. Some lichen house both algae and cyanobacteria in a single fungal structure. The fungus is the body of the lichen giving it shape and also providing its reproductive structures. Lichen can reproduce both sexually, producing spores, and asexually by simply breaking apart
There are three basic forms of lichen growth. If the growth form is somewhat leafy in shape it is referred to as foliose. Fruticose lichens are somewhat tufted or bushy, and crustose lichen appears more or less like a coat of paint often on a rock or tree trunk.
You can find many different species growing on the bark of a single tree, covering a stone wall, or on a bare soil slope on the side of a road. They give color and texture to our world. Below is a photo of a tree in my neighborhood that has at least 5 different species of lichens growing in one small area.
And what of color? They are every hue of green, grey-green, blue-green, yellow-green but also red, vibrant yellow, orange, brown and black. When pointing out lichen to students (I teach at a local college) I ask them to picture the scene without lichen. It would be a bland one indeed, with less color or texture. And as Thoreau in the quote above points out, on a wet or foggy day they will absorb the surrounding moisture and swell with vibrant colors that they just hint at when lacking moisture during a dry spell. On a rainy day, take a good look at the bark of almost any tree and you’ll see vibrant lichen covering it.
Lichens cover about 6% of the earth’s surface and provide many uses to organisms, us included, as well as what is know as ecosystem services. Humans use lichens in perfumes, as dyes for wool and fabric, and some lichen have even been used for food. Other animals such as reindeer and turkey depend on lichen for food. Lichens stabilize soil thereby preventing erosion. They contribute to soil formation by trapping dust and particles. Take a close look at lichen covering a rock and you’ll see the build up of soil. Even though our atmosphere is mostly made of nitrogen it is in a form unavailable for use by other organisms. Lichens can fix (capture) nitrogen, turning it into a useable form and so making this important element available for use by plants. They can predict air pollution because many are pollution sensitive. The lack of certain species in a place that they were previously found in is an indicator of ecosystem problems, a sort of canary in a coal mine. The US Forestry Service use lichens as an early warning system to monitor air pollution in our nation’s protected forests. Lichens can store various substances within their structures that can then be analyzed for pollutants found in the air. (1) And they provide excellent habitat for many types of invertebrates. When observing lichen with a microscope finding tiny mites and beetles is not at all uncommon.
While on one of my regular walks to Pegotty Beach in Scituate, MA, the town I was lucky enough to grow up in, I noticed this beautiful yellow-orange lichen growing on a pile of stones at the base of a driveway near the beach. No one seemed to be around and it was too tempting not to take a photo or two for a positive ID later. Somewhat embarrassingly for me, the owner of the house pulled up as I was bent over photographing the rocks. I apologized explaining that I was admiring his lichens. Though he was pleasant enough I can’t help but think he was questioning my sanity. They were, however, beautiful Xanthoria parietina, or maritime sunburst lichen. An apt name for this brilliant yellow lichen often found near the coast on rocks or bark. Once you start to look for it you’ll see it often.
Xanthoria parietina,maritime sunburst lichen
Lichens are macroscopic organisms for the most part, that is you can see them without magnification. But, some of the structures are better observed with a hand lens or even a microscope. For example, to observe spore structure within the body (thallus) of the lichen a scope is a must. Often a hand lens will do just fine, especially lichen hunting in the field. During my first field seminar on Lichen Ecology with Dr. Mark Seward and Dr.David Richardson at the Humbolt Institute in Steuben, Maine we went to the nearby town of Milbridge to collect lichen for identification back in the lab. I was enthusiastically gathering lichens and trying to learn all of could from my two teachers. We were in what could be called the downtown area that, to the best of my recollection, consisted of a few tree-lined roads with little markets, a laundry mat, and a gas station and some restaurants. All armed with our hand lenses, perhaps eight from the class were jostling for real estate around a particular tree to observe whatever lichens one or the other of our teachers was pointing out. Mind you to observe lichen with a hand lens you must be just a few inches from the tree. It all of a sudden occurred to me how strange our group must appear to any down Mainer that happened to look our way. Essentially, we were a bunch of nerds all gathered around a tree trunk, our noses inches from the bark. As funny as this seemed to me, it didn’t deter me from continuing my enthusiastic quest for knowledge about this yet unexplored (for me) piece of diversity.
I’m sure that each person has a favorite lichen species. My favorites, discussed below, are common and you can find them fairly.
Lobaria pulmonaria
To me Lobaria pulmonaria is a breath-taking lichen, especially after a rain. When it’s dry, it appears rather drab and brown. But after absorbing moisture it expands to a lush shade of green. As it’s scientific name suggests it looks like expanding lungs and a common name is lungwort lichen. It’s more often found near the coast and in moist forests. I tend to see it along the coast of Maine growing on the barks of deciduous trees like oak or maple. It is sensitive to pollution and has experienced significant habitat loss and so is considered rare or endangered in many parts of the world. This, in my mind, makes it all the more special to find. It’s one of the lichen species that consists of a three-way symbiosis (also really cool); the fungal thallus, and two photobionts, a cyanobacteria, Nostoc,and green algae Dictyochloropsis reticulate. It is reported to have anti-inflammatory effects (2) and has also been used to dye wool orange and in the manufacture of perfume. (3)
Lobaria pulmonaria, lungwort
Usnea- In the photo below Usnea is the tufted lichen in the center of the photo.
Another favorite type of lichen is Usnea (there are many species), or beard lichen. Growing in fruticose form on both conifers and deciduous trees in bushy little tufts of light gray-green it is quite easy to spot. Being very pollution sensitive it will not grow in areas with a lot of pollution so you will have difficulty finding it in a city. I see it a lot walking around my suburban neighborhood (shown in the photo above). It’s also fairly abundant on Cape Cod in various scrub forests that are a common habitat there. If you type Usnea into a search engine most of what ‘pops up’ are sites for medicinal uses of this lichen. It is purported to have antibiotic, anti-inflammatory, and analgesic properties. Since it is also said to cause acute liver damage, my advice is to admire it from afar, or under a microscope.
Diabaeis baeomyces – pink earth lichen
Diabaeis baeomyces – pink earth lichen
This beautiful soil binding fruticose lichen is easy to spot, especially along roadway inclines. The thallus is a pale gray making it is easily identified even while driving down the road. The prettiest part of this lichen is the reproductive structures, or apothecia, which look like little pink lollipops. It is found along eastern North America and functions as a very good stabilizer of soils.
Cladonia cristatella (and some other Cladonia species)
Lichen with growth forms similar to Diabaeis are species of Cladonia, a common one the British soldier lichen. The name is derived from the fact that the apothecia are bright red and resemble the hats of the British Soldiers of colonial days. These Cladonia are found growing on soil, rocks (covered with a film of soil), in moss and on rotting wood. They are very sensitive to pollution. These decomposers are nitrogen fixers, can serve as shelter for insects and food for turkeys and rodents. And they are beautiful to behold.
1. Magazine,November 15, 2016, 1. Lichens are an early warning system for forest health, by Amy MacDermot, Science News
2.. Süleyman, H; Odabasoglu, F; Aslan, A; Cakir, A; Karagoz, Y; Gocer, F; Halici, M; Bayir, Y (2003). "Anti-inflammatory and antiulcerogenic effects of the aqueous extract of Lobaria pulmonaria (L.) Hoffm". Phytomedicine. 10(6–7): 552–7. doi:10.1078/094471103322331539. PMID 13678242.
3. Llano GA (1948). "Economic uses for lichens". Economic Botany. 2 (1): 15–45. doi:10.1007/BF02907917.