Wetland Plant Series: Lichens

By Aaliyah Ross, Environmental Educator

This installment of the wetland plant series focuses on an organism that isn’t actually a plant. In fact, it isn’t even a single organism. Although they are often studied alongside nonvascular plants like mosses and liverworts, lichens are their own distinct and very unique group of organisms.

What is a Lichen?

Reindeer moss, a fruticose lichen, on the ground near the Beaver Dam Trail.
Reindeer moss, a fruticose lichen, on the ground near the Beaver Dam Trail.

Lichens evolved as a symbiotic relationship between a fungus and another organism that produces food through photosynthesis (called a photobiont). The photobiont in a lichen can either be an algae, cyanobacteria (also known as blue green algae) or both. The photobiont provides a source of food while the fungus provides protection by enveloping the photobiont within its tissues, and provides moisture to the photobiont by transporting water directly into its cell walls. Therefore, a lichen can be considered an extreme example of symbiosis because the photobiont (either algae or bacteria or both) lives within the fungus’s tissues. It is a true composite organism.

Where do Lichens Live?

Foliose lichen on a cypress tree, Phinizy Center campus.
Foliose lichen on a cypress tree, Phinizy Center campus.

Lichens cover approximately 8% of the Earth’s surface. They live on trees, rocks, and soil, as well as on manmade objects like concrete and wooden surfaces. They are found everywhere from the poles to the tropics and from intertidal zones to mountaintops. They are abundant throughout Phinizy Swamp Nature Park as well. The next time you’re on a walk, take note of how many lichens you can see. Once you start paying attention to lichens, it can be hard not to notice them!

What do Lichens Look Like?

Brightly colored lichens cover the ground at Heggie’s Rock Preserve in Appling, GA.
Brightly colored lichens cover the ground at Heggie’s Rock Preserve in Appling, GA.

The appearance of lichens is incredibly diverse; some are dull green, gray, slate blue, black or brown, while others feature bright red, orange, or yellow colors. Lichens can be grouped into three categories based on body form: Foliose lichens have leaf-like lobes, fruticose lichens are “shrubby” in appearance, and crustose lichens have a crust-like form that is often tightly embedded onto trees, rocks, or manmade surfaces.

What can Lichens Tell us about Air Quality?

Crustose lichen on a tree branch, Beaver Dam Trail.
Crustose lichen on a tree branch, Beaver Dam Trail.

Lichens are extremely sensitive to air pollution because they rapidly absorb compounds from the air and rainwater. If a pollutant even slightly damages one component of the lichen, the partnership will quickly break down and the lichen will die. The more of a lichen’s surface is exposed to the air, the more sensitive to air pollution it will be. Lichens are completely absent in the zone closest to a source of air pollution. Farther away, pollution tolerant crustose lichens begin to appear. Fruticose lichens are generally most sensitive to air pollution; a high abundance of fruticose lichens in area is an indicator of good air quality.