If you frequent nature trails, you have likely passed by stones or trees with some kind of crusty material on the surface.  Is it a moss?  No, moss is a plant.  Is it a fungus?  Well, yes and no.  This crust is actually a partnership between at least two different organisms, making a composite organism called lichen (pronounced “LIKE-en”).

Lichens are made of multiple fungi – a diverse group of organisms including mushrooms, molds, yeasts, and others – living with algae and/or algae-like bacteria called cyanobacteria.  The fungi provide a pleasant, hydrated shelter to live in, while their partner provides food through photosynthesis.  Photosynthesis means using sunlight, water, and CO₂ to create sugar (and the oxygen that we breathe, no big deal).  Cyanobacteria can also “fix” or make use of nutrients from the air, further helping the fungi to grow.  This mutual relationship between different species is what biologists call symbiosis.

Thanks to the many possible fungi-algae-bacteria combinations, lichens take on many different forms and colors.  In New York State alone, there are over 800 types of lichens!  Lichens can look like small flaky crusts (“crustose”), flat leaf-like growths (“foliose”), or even branched (“fruticose”) like miniature shrubs.   Many take on a greenish-grey hue, but other colors include brown, black, white, yellow, bright orange, red, and blue.  You might see these unique fungal partnerships on all kinds of surfaces along nature trails – adding a nice flair to wooden sign posts, historic stone walls, boulders, tree bark, the forest floor, and decaying logs.

Cultural Significance

People have used lichens for a variety of purposes for thousands of years.  Lichens with antibiotic properties have been used in traditional medicines and embalming practices.  Some of the more brilliant-colored lichens have been used to make dyes for yarn, cloth, and even litmus paper (a quick, easy way to measure how acidic something is).   Several cultures worldwide include lichens in their diets, making soups, side dishes, beverages, and even molasses.  But watch out – not all lichens are safe to eat!  Those involving cyanobacteria can produce toxins; these lichens have historically been used as poisons in hunting.

While all these uses of lichens are interesting, we at New York State Parks want you to simply enjoy observing the beauty and impact of lichens in their natural habitats.

Lichens in Nature

Lichens serve several important roles in our parks.  As one of the first lifeforms that established on land, they helped create much of the world we live in today.  They play a role in soil formation, slowly breaking large rocks down into smaller pieces.  Then they carry out processes that add essential nutrition to forest soils, allowing trees and plants to grow.  Lichens also benefit wildlife.  Northern flying squirrels, deer, and moose are among those known to graze on lichens, particularly in the winter.  In the spring, birds like the Ruby-throated Hummingbird and the Blue-Grey Gnatcatcher often use lichen to build and camouflage their nests.

Lichen populations also give important clues about environmental health.  Studies have shown lichen to be sensitive to air pollution, and so a decline in lichen may be a warning sign of worsening air quality nearby.  Similarly, lichen growth rates react to long-term changes in moisture and temperature, and so they can help monitor the climate.  Scientists take advantage of the slow-growing nature of certain lichens and use their size or branching patterns to estimate the age of rocks in the forests, similar to tree rings on a tree stump.

By keeping an eye on the lichens in our parks, we can discover fascinating patterns in our local ecosystems.  And we can have a deeper appreciation for the beautiful landscapes that New York State has to offer!

See if you can spot these and other lichens the next time you are out enjoying nature:

Reindeer moss (Cladonia rangiferina) in the winter. Despite the name, this is actually a lichen. There are many similar species of Cladonia that can be seen in New York State Parks. (Photo by Steve Young, NYNHP)

Grey rock tripe (Umbilicaria sp.) and a finely-textured crustose lichen on a cliff community. (Photo by Gregory Edinger, NYNHP)

This spongy gray-green lichen was found in a chestnut oak forest. (Photo by Gregory Edinger, NYNHP)

Orange-brown rock tripe (Umbilicaria sp.) can be found on big rocks and outcrops at State Parks such as Minnewaska, Sterling, Moreau, and others. (Photo by Steve Young, NYNHP)

Up-close and personal with a leaf-like (“foliose”) lichen on a tree in Thacher State Park. (Photo by Erin Lennon, NYS Parks)

Stepping back to admire a mix of foliose lichens (grey and light-green), crustose lichen (small golden speckles), and moss (dark green) on the same tree trunk at Thacher State Park. (Photo by Erin Lennon, NYS Parks)

Post by Erin Lennon, State Parks

Featured image:  A common sight: lichen attached to tree bark in New York State. (Photo adapted from Wikipedia, public domain)

Resources:

Video featured on NPR’s Science Friday: “Hunting Wild Lichen.”

U.S. Forest Service factsheet: “Lichens – Did you Know?”

BBC article on soils and lichen in creating the planet we know today. http://www.bbc.com/earth/story/20151205-one-amazing-substance-allowed-life-to-thrive-on-land

NYT article on a 2016 ground-breaking discovery that yeasts are an additional part of many lichens: “Two’s Company, Three’s a Lichen?”

List of the Lichens of New York, by Richard Harris in 2004.