Not everyone knows what a lichen looks like, and many of us have little knowledge of what they are, how they live or why they are so beneficial to our lives. Here’s a primer to notch up your know-how when it comes to these complex and fascinating life forms that thrive in the Upper Delaware River region. 

As described by the U.S. Forest Service, lichens represent a symbiotic partnership of two separate organisms—a fungus and an alga. The primary partner is the fungus, which gives the lichen its dominant characteristics, while the alga can be a blue-green alga—otherwise known as cyanobacteria—or a green alga, or both.

Fungi lack chlorophyll or a means of producing their own food. That’s where the relationship with algae comes in. This partnership provides the means for fungi to gain nutrients from another organism through the aid of the alga, which photosynthesizes and provides food for the fungus to grow.

There are three main types of lichens. Foliose lichens have easily distinguishable top and bottom sides and can be very flat or leafy like lettuce. They might also display ridges, bumps and fringed lobes. 

Fruticose lichens can be hair-like, upright and shrubby, or cup-like. Some have round branches with a central core and others are hollow in the middle, while yet others have flat branches that tangle together. Crustose lichens, as their name implies, form colorful crusts over surfaces such as rocks, trees and even roof shingles. 

So where do lichens like to live? On top of something else (such as a tombstone) that stays still long enough for the lichen to attach to the surface, or substrate. Lichens can occur on various substrates, as long as the substrate provides access to water, air, light and nutrients such as oxygen, carbon and nitrogen. 

Both animals and humans make good use of lichens, which provide building materials, shelter and forage for birds, insects and some mammals. Humans use lichens for dyes, decoration, teas and even products such as toothpaste and deodorants. Some lichens are edible, while others are toxic. 

Lichens need clean fresh air to survive as they absorb everything from beneficial nutrients to harmful toxins, which explains why they don’t thrive near sources of pollution. If you are seeing lots of lichens on the rocks and trees around your home, it’s an indicator that the air you are breathing is clean and healthy—for you and the other humans and animals sharing your neighborhood. 

Take a walk today and look for the lichens living near you. Give them a nod of gratitude for all they are doing as silent partners supporting your health and wellness, just by being there.

Visit www.gis.nacse.org/lichenair/ to learn more about the U.S. Forest Service’s National Lichens and Air Quality Database and Clearinghouse, which is devoted to lichen biomonitoring and assessing the ecological impacts of air pollutants.