What the Heck is a Lichen?

When my sister and I were little, my parents often took us camping in Colorado during the summers. We brought our Barbie dolls and when evening came around, we built pretend campfires and served pretend food. Part of those imaginative meals included lichen fragments we’d taken from rocks, and we served them to our dolls as “cornflakes.” As innocent as this image might be, one should not pour milk on lichens. They obviously aren’t cereal, nor are they mosses or even plants. Lichens are complex organisms created by what is currently understood as a symbiotic relationship between a fungus and an algae or cyanobacteria. Sometimes it’s both. With approximately 3600 species, they are nothing short of fascinating.

In a symbiotic partnership, the fungus is the dominant partner and the one that gives the lichen its distinct characteristics. But why does the fungus even pair up in the first place? Fungi don’t have chlorophyll, a compound present in green plants that gives them their color as well as allowing them to absorb energy from the sun. This means fungi depend on other living things to photosynthesize for their nutritional supply. So for lichens, that partner is algae or cyanobacteria. Cyanobacteria can also provide fungi with another benefit: that of nitrogen fixation.

But what do algae and cyanobacteria get in return? The fungi provide a more protected environment allowing them to survive in harsh environments where algae or cyanobacteria would not normally be able to. The fungi can create a “shell” with pigments that absorb harmful UV light.

Liz Bowman, Fungal Ecologist in the Department of Integrative Biology offers an even more complex understanding of lichens. “One of the biggest debates among lichenologists is whether the fungal-photobiont relationship is mutualistic or parasitic,” she says. “Honestly, it probably varies across species and environmental conditions, but has yet to be fully researched.”

Sometimes, the life that comprises a lichen is also just as complex. Liz explains: “Recently, there have been more studies looking at what other organisms are found within lichen thalli, or body. Some researchers have found that in addition to algae and cyanobacteria, lichen thalli host a very diverse community of fungi and bacteria.”

Lichens are commonly associated with mosses, but are actually very different. The chloroplasts in lichens are contained in the surface of the lichen as well. Liz explains that for over 100 years, lichenologists have been trying to artificially synthesize the object of their study, not an uncommon practice in the science community. However, these attempts have mostly failed. “There are some theories,” Liz says, “that these communities of fungi and bacteria within lichens might be important for the formation of lichens, but as far as I’m aware, no one has tested that.”

Lichens provide a lot of ecological services. Because of the high surface area to volume ratio of lichens, it makes them particularly vulnerable to air and water pollution. Scientists can extract the toxins they absorb and determine levels present in the atmosphere, and thus the health of the environment. In Britain, for example, the Lungwort, or "lung lichen,” (Lobaria pulmonaria) is used as an indicator of undisturbed ecosystems.

In many dry areas of the world where there is no human or livestock disturbance, carpets of lichens, bryophytes and cyanobacteria (otherwise called “biological soil crusts”) can prevent soil erosion when those infrequent but heavy rains appear. In these environments, they also prevent wind erosion.

For wildlife, they provide food and shelter. Many species of birds and squirrels use them for nests. Low in protein but high in carbohydrates, they are one of the few foods available in areas where winters are very cold. Many species of deer, mountain goat, antelope, and caribou depend on them for part of their diet. Small mammals like flying squirrels, rabbits, and voles also consume them. Some amphibians use lichens as camouflage.

Because lichens can survive in harsher environments, this means that algae can convert carbon dioxide in the atmosphere in places it normally would not be able to. They also grow on some of the most challenging surfaces: rocks, metal, plastic, cloth, and sides of buildings like on many of the old churches in parts of Europe. This is because lichens can absorb water through any part of their thalli and have no need of roots.

And then there is just pure aesthetics of lichens. With their other-worldly qualities, they inspire wonder and creativity for many of us, including imaginative children making camping meals for their dolls.

LICHENS AT OUR OWN FIELD STATIONS

Stengl Lost Pines Biological Station (SLP) is one of our field stations where lichens are found. The Resident Manager of SLP, Steven Gibson, explains it as such: “The field station is located within the Lost Pines of Bastrop county, and is a sub-habitat with a unique blend of plants and animals. Some are familiar Central Texas species and others are typically found much farther east and associated with Eastern forest systems.” Some of the better-known examples are trees like the Loblolly Pines and flowering Dogwoods. But as Steven works closely with the land at SLP, he knows that there are other life forms, like lichens, that are equally removed from their expected ranges.

Two species are Cladonia parasitica and Cladonia subtenuis. “Of particular interest is the presence of C. parasitica,” Steven says. “It is often used as a signal species, indicating high-value old-growth forest. So in the case of SLP, this is a testament to the quality and state of the forest at Stengl. It reinforces some of the important components of habitat management of the field station.”

And what components might those be? Steven continues: “One in particular is when we leave decaying tree fall in place on the forest floor. Without such substrate, it is unlikely this species of lichen would be found.” Tree fall provides habitat not just for this lichen but also other fungi and insects. “These species remind us that forest management is not always what is done, but sometimes what is left undisturbed,” Steven explains. “Such mature systems with diverse age structures and varying canopies, understories, and ground cover are invaluable to research and teaching.”

In our follow up blog, we’ll look at the role lichens have in human culture, in the past and the present.

SOURCES

“About Lichens” U.S. Forest Service, United States Department of Agriculture (https://www.fs.fed.us/wildflowers/beauty/lichens/about.shtml)

“Biological Soil Crusts” Australian Lichens. (https://www.anbg.gov.au/lichen/ecology-soil-crusts.html)

“The Hidden World of Lichens With Felicity Roberts.” Atlas Obscura online courses. July 2021. (https://www.atlasobscura.com/experiences/lichens-online-course)

Machesney, Dianne. "Lichen in the Garden." February 12, 2020. PennState Extention. (https://extension.psu.edu/lichen-in-the-garden)

Plitt, Charles C. 1919. A short history of lichenology. The Bryologist. 22: 77-85.

Sharnoff, Stephen and Rosentreter, Roger (Bureau of Land Management, Idaho) “Lichen Use By Wildlife in North America,” Lichens of North America Information, Feb 2, 1998.