Being able to identify and appreciate lichens can add excitement to pretty much any adventure, anywhere. Lichens are beautiful, fascinating, and present everywhere from city streets to the shores of Antarctica. No matter where you are, lichens exist in almost every environment.
In fact, they’re some of the first colonizers that will begin the progression of life in a new space. Whether it’s an abandoned gravel pit, a brand-new sidewalk, or a recently deglaciated slope, lichens are often among the first non-microscopic life forms to appear in a new area.
Why should you learn about lichens?
Once you start noticing lichens, you’ll probably see some beautiful ones. Pictures of these are great conversation starters on a first date or at a family gathering.
You can tell your friends all about your newfound passion for lichens.
It’s fun and easy to learn how to identify major categories of lichens.
You might make cool friends by getting involved in a citizen science program that measures lichens to monitor air quality.
You can begin using the phrase “lichen up” as an alternative to “man up,” emphasizing extreme teamwork and extreme toughness.
So what are lichens?
Nope, not Lycans. Lichens.
There we go! That’s a great example of a Foliose lichen growing on a tree.
Rather than being a single organism, a lichen is actually a set of multiple organisms that work as a team to satisfy their basic needs for life.
Fungi + Algae and/or Cyanobacteria = Lichen
Fungi are really tough and adaptable organisms, but they aren’t able to produce food from sunlight in the way that plants can. That means that most fungi need to feed on another substance in order to get food – for example, by growing on rotting wood (mushrooms) or old bread (mold).
However, in a lichen, the fungal part of the lichen provides a shelter to house some algae and/or cyanobacteria. In return, the algae or cyanobacteria is able to photosynthesize (create food from sunlight) and provide that energy to the fungal partners. The algae and/or cyanobacteria get a nice place to live, and the fungi receive food from these photosynthetic lodgers.
Although it was previously believed that the fungal part of the lichen consisted of a single type of fungus, researchers discovered in 2016 that yeasts also serve as an important partner in many lichens. Although certain strains of yeasts are used to make your bread rise, yeasts are actually an enormous category of microscopic fungi with diverse roles in nature. In a lichen, the yeasts are thought to protect their little community by shielding the larger fungus and its algae from stressful situations.
As a community, a lichen is able to get food from photosynthesis, protect itself from various hazards such as dry weather, and derive any needed minerals from rocks, trees, or whatever surface the lichen grows on. That’s pretty extreme teamwork.
What do lichens look like?
Lichens come in lots of different shapes, textures, and sizes. They tend to get mistaken for moss, but have a texture and color that’s different from moss. Due to being complex symbiotic organisms, particular lichen species can be tricky to identify. However, it’s very easy to learn the three major categories of lichen types: foliose, crustose, and fruticose. Foliose lichens have leafy-looking bodies which appear different on the top and the underside. Crustose lichens cling so tightly to the surface they grow on that you can’t see the underside at all. And fruticose lichens are hair-like, bushy, or highly 3-dimensional with no obvious difference between the top and the bottom of the body.
Here are some examples of lichens from North and Central America:
This first picture shows a lichen that, from a distance, looks like a paint splatter on a tree. However, if you look at it more closely, it has a somewhat fuzzy texture and an organized green/white transition zone. Crustose lichens such as this one can be found on the bark of many trees both in cities and in the woods, although many of them are all-white in color. If you look at the rest of the bark in this photograph, the dark green fuzzy stuff is moss, which is an unrelated life form that we’ll talk about another day.
The lichen in this second picture is also growing on a tree, but this fruticose variety looks more like weird land-based seaweed. Unlike moss, this lichen is more grey than green, and the texture of each individual piece is sort of leathery when wet.
This third picture shows one of my favorite types of fruticose lichen, often nicknamed toy soldier lichen. Once again, note how the color is fairly grey, and the texture is bumpy but not fuzzy like moss would be.
This fourth and final picture is a little trickier, because both moss and lichen are growing in the same spot, and they look fairly similar in structure. You can tell the two apart by the fact that the moss on top is brighter green and has a fuzzier surface. The fruticose lichen, on the other hand, is more grey in color and has a smoother surface.
If you’re interested in learning more about the different categories and species of lichens, this U.S. Forest Service pamphlet is a great starter guide. It’s focused on Alaska, but the explanations are generalizable to common lichens throughout the world.
What makes lichens cool?
They can eat rock
Many lichens are able to grow on rocks, using this surface for shelter and as a source of nutrients. The lichen is literally strong enough to break apart little bits of the surface of a rock, and many lichens also dissolve the surface of the rock with acid.
Luckily for us humans, the acid is produced in small amounts over a long period of time, so you aren’t going to accidentally dissolve part of your hand by touching a lichen. These miniscule quantities of acid work over a long time to break down relatively small amounts of rock, which the lichen can then use for nutrients.
Certain species can survive in outer space
Incredibly, a certain type of lichen has been shown to be able to survive for a year and a half in outer space! This absurdly tough space adventurer is called elegant sunburst lichen, and it likes to grow on rocks all over the planet. In addition to being totally awesome, elegant sunburst lichen’s hardiness gives scientists some additional clues about whether it’s really possible for life to survive on Mars.
Lichens may be unobtrusive, but they’re definitely one of the toughest life-forms you’ll see around your neighborhood.
Lichens are ecosystem pioneers
Partly because it’s so tough and needs so few resources, lichen is often one of the first pioneers in a newly establishing ecosystem. A recently abandoned gravel quarry in Indiana, for example, is a tough place to live. The lack of soil means that plants can’t grow, and without plants the quarry doesn’t provide any shelter or food for larger organisms.
Over time, lichens will begin to establish themselves in nooks and crannies within the quarry. Each lichen provides shelter for a tiny world of microbes ranging from bacteria to tardigrades. Because the surface of the lichen is textured and the lichen is able to break down rock, the area surrounding the lichen will gradually build up a small pile of organic matter. On top of this organic matter, moss may be able to begin establishing itself, which provides habitat for slightly larger critters such as insects. Over time, even more organic matter is able to build up there, creating enough soil for small plants to begin growing. This attracts larger critters, allows for more organic matter to accumulate, and BAM! next thing you know you’ve got a forest growing in the old gravel pit. Well, it actually may take a few centuries, but you get the idea.
Lichens are really important to mature ecosystems as well. Lichens form part of the biological soil crusts that are so important to life in dry areas. Lichens absorb toxins from the air. They’re an important food source for certain animals, and they contribute to important decomposition in harsh places.
Like any superhero, Lichen does have a weakness
For many species of lichen, air pollution is their kryptonite. Because the lichens absorb toxins from the air, an excess of toxins can kill a lichen by gradually accumulating inside its body until it reaches a level that’s not tolerable. That means many species are slow to grow in areas with significant air pollution, such as smoggy cities. In fact, scientists often use lichens as indicators of average air quality in a particular area.
How can you appreciate lichens?
Lichens are pretty awesome. They are:
A character study in toughness, teamwork, and new beginnings
Critical founding members of the ecosystems we enjoy
The next few times you’re walking outside, look at trees, rocks, or stone walls as you pass them. Do you see any lichens? What do they look like? Are they crustose, foliose, or fruticose? How do they compare to lichens you see in a different area?
Spribille, T., Tuovinen, V., Resl, P., Vanderpool, D., Wolinksi, H., Aime, M.C., Schneider, K.,… McCutcheon, J.P. (2016). Basidiomycete yeasts in the cortex of ascomycete macrolichens. Science
353(6298), 488-492. doi: 10.1126/science.aaf8287
Chen, J., Blume, H., Beyer, L. (1999). Weathering of rocks induced by lichen colonization - a review. Catena 39(2000), 121-146. Retrieved from http://pages.mtu.edu/~raman/SilverI/MiTEP_ESI-2/Lichen_Rings_files/ChenetalCatena.pdf
May, P.F. (2000). How to identify a macrolichen (online). Farlow Herbarium, Harvard University, Cambridge, Massachusetts. Retrieved from http://www.huh.harvard.edu/collections/lichens/howto.html