Lichens 101: What They Are & Why They Matter

The article below is based on a podcast interview with Jessica Allen.

Ever wonder what those colorful splotches clinging to rocks and trees actually are? They’re not plants but something else entirely different: lichens! These champions of resilience can survive on everything from your mailbox to the frigid tundra. But beyond their impressive adaptability, lichens hold a secret world within. They’re not single organisms but complex partnerships between a fungus and an algae or bacteria, creating a miniature ecosystem teeming with life.

Intrigued? You should be! But what in the world are these organisms doing?

In this blog post, we’ll explore the fascinating biology of lichens, uncover their hidden complexity (including the menagerie of bacteria, fungi, and even tiny animals that call them home!), and discover the surprising ways they benefit our planet. We’ll learn how lichens can thrive in unexpected places, from rocks you pass along a hiking trail to discarded furniture, and unravel the clever ways they tap into multiple nutrient sources. We’ll also explore how scientists use lichens to track air quality changes and how humans have used them as textile dyes, fragrances, and medicine. Get ready to have the world of lichens opened up to you!

What are lichens?

Lichens, those fascinating organisms you often see clinging to rocks or trees, are a symbiotic relationship between a fungus and an alga or cyanobacteria (also known as blue-green algae). The fungus provides the structure, like the walls of a house, while the algae or cyanobacteria captures sunlight and produces sugars through photosynthesis. This mutually beneficial partnership allows lichens to thrive in harsh environments where neither organism can survive alone.

Lichens: a universe within

But the lichen story doesn’t end there. Recent discoveries have revealed a surprising level of complexity. Beyond the main fungal partner and single-celled algae, lichens often harbor a diverse community of bacteria, other fungi, and even tiny multicellular animals like tardigrades and nematodes. So, lichens are actually miniature ecosystems teeming with a diverse community of microbes. Scientists are still unraveling the web of interactions within these miniature worlds.

But what does this all look like? Imagine peering into a slice of lichen through a microscope. You’d see thread-like fungal cells alongside larger, round, green algae cells. Tardigrades, larger than both, would lumber about, while even smaller bacteria would be scattered throughout. Some bacteria live nestled within the lichen, while others thrive in the outer layers.

The bacterial community within lichens is particularly fascinating. Studies show that these communities are incredibly abundant and diverse. Scientists are now zeroing in on a core microbiome, a group of bacteria consistently found across different lichen species. This core group may play a vital, yet previously overlooked, role in the lichen symbiosis.

The concept of lichens as miniature ecosystems sheds light on a bigger picture. It highlights the interconnectedness of life on Earth and reminds us that life on Earth is often a collaborative effort. Just like lichens, our own bodies and the environment around us are teeming with microbial communities, each playing a role in the intricate dance of life. Thinking about lichens helps us appreciate the remarkable complexity of life on a microscopic scale despite a seemingly simple exterior.

Important roles of lichens

Lichens play some vital roles in our world. They may be small, but their impact is far-reaching.

• Food: Lichens are a critical food source for a diverse range of herbivores. From tiny insects like mites and springtails to much larger grazers like rabbits, mountain goats, and even moose, lichens provide sustenance throughout the year. For caribou and reindeer, lichens are especially important, forming a significant portion of their winter diet. The decline of caribou populations in North America is partly linked to habitat loss that reduces the availability of these nutritious food sources.
• Nesting materials: Lichens also serve as nesting material for birds and squirrels.
• Camouflage: Many insects, like longhorn beetles and caterpillars, use lichens for camouflage, blending in perfectly with their mottled colors and textures. The larvae of lacewings take lichen camouflage a step further. They meticulously construct elaborate protective shells from a specific type of lichen called “fairy dust lichen.” These tiny suits of armor not only camouflage the lacewing larvae but also offer water-repellent protection.
• Nitrogen Fixation: Lichens also play a crucial role in ecosystem health. Certain lichen species have a symbiotic relationship with cyanobacteria, also known as blue-green algae. These cyanobacteria can capture nitrogen from the air and convert it into a form that other organisms can use for growth and development. This process, called nitrogen fixation, is particularly important in nitrogen-poor environments like high mountain ranges and tundra regions.
• Soil Stabilization: In drier areas, lichens contribute to soil stability by forming a protective crust on the surface. This biological soil crust, a combination of free-living cyanobacteria, mosses, and lichens, helps prevent wind and water erosion, safeguarding the delicate balance of the ecosystem.

Lichens substrates: lichens found in unexpected places

Lichens can be found in a wider variety of locations than you might think. They’re not picky about where they set up shop as long as it fulfills a few requirements:

• Stability is key for a lichen to thrive. The surface it grows on needs to be relatively stable and undisturbed.
• Good air quality is essential.
• Lichens prefer areas with moderate humidity and some rainfall.
• Sufficient sunlight for photosynthesis by the algal partner is necessary as well.

While some lichens are particular about their real estate, others are surprisingly adaptable. Certain species have very specific requirements, only growing on a particular type of bark or in a specific location on a plant.

On the other hand, some lichens are happy to call almost anything home. Cowboy boots, discarded tin cans, traffic signs, discarded furniture, and even rusting cars can provide suitable surfaces for these tenacious organisms.

So, next time you’re out and about, take a closer look at the world around you. You might be surprised by the unexpected places where lichens have set up home!

How do lichens get their nutrients?

Lichens have a knack for finding sustenance in unexpected places. They may attach themselves to rocks, trees, mailboxes, or even discarded furniture, but how exactly do they get the nutrients they need to thrive?

The answer lies in a combination of the unique partnership between the fungus and algae or cyanobacteria within the lichen and the clever ways they interact with their environment. We know that the algae partner in the lichen is responsible for photosynthesis, creating sugars that nourish both organisms. But that’s not the whole story.

Lichens also benefit from a constant rain of tiny nutrient particles carried by the wind. This “atmospheric deposition” provides essential elements for growth and development. Interestingly, air pollution can also play a role in this process, although not in a positive way. Lichens can be sensitive to pollutants, and scientists are studying how air quality affects their health.

The way a lichen attaches to its substrate can also influence its nutrition. Some lichens secrete sugary compounds that act as a glue, adhering them to the surface. Others send thread-like fungal cells into the substrate itself. For lichens growing on rocks, these fungal cells may even secrete acids that help break down the rock, potentially providing additional nutrients. In this case, the lichen grows into the rocks itself.

This ability to tap into multiple nutrient sources is a key factor behind the ubiquity of lichens. Their symbiotic relationship allows them to be relatively self-sufficient, surviving in a wide range of environments. While they may obtain some nutrients from their substrate, they’re not solely reliant on it. This flexibility is what allows them to thrive on everything from natural surfaces like rocks and trees to the most unexpected human-made objects.

Where are lichens unable to live?

Lichens can be found in a surprisingly wide range of habitats, but even these versatile organisms have their limits.

Most lichens are terrestrial, meaning they prefer land-based environments. While there are a small number of freshwater and marine lichen species, they are the exception rather than the rule. Deepwater environments are simply not suitable for lichens.

Another factor that can influence lichen abundance is competition from other organisms. In areas with lush carpets of moss, lichens may be less common. The mosses effectively outcompete the lichens for space and resources.

Surprisingly, cities can be a mixed bag for lichen diversity. Some urban areas, particularly those with a history of good air quality, can support a surprising abundance and variety of lichens. However, cities with poor air quality can be harsh environments for lichens, leading to lower diversity and abundance.

Lichen distribution depends on a complex interplay of factors. While they are quite adaptable, some environments simply aren’t hospitable to them.

Lichens as air quality monitors

Lichens can serve as indicator organisms, offering valuable clues about the quality of the air around us because they are sensitive to sulfur-based air pollutants.

The Industrial Revolution saw a dramatic increase in these pollutants, leading to a decline in lichen diversity and abundance in many areas. However, stricter air quality regulations, like the Clean Air Act, have led to a decrease in sulfur-based pollutants and, in turn, a resurgence of lichens in many cities.

While sulfur dioxide levels have declined, nitrogen deposition has become a growing concern. High-nitrogen environments favor a smaller subset of lichen species, with most preferring environments lower in nitrogen. Scientists are now monitoring lichens to track changes in nitrogen deposition as well.

Lichens can also act as bioaccumulators, taking up heavy metals and radioactive materials from the environment. This makes them valuable tools for identifying localized pollution sources, such as old mining sites or areas impacted by nuclear waste. Unlike trees, which can shed leaves or have a protective waxy coating, lichens are constantly exposed to the elements. They absorb everything from the air, acting as a record of what’s happening in their environment.

This unique characteristic makes lichens ideal for use in air quality monitoring programs. By studying the types and abundance of lichens in a particular area, scientists can gain valuable insights into the types and levels of air pollutants present. This approach is not only cost-effective compared to traditional air quality monitoring methods, but it also provides information about long-term trends. By revisiting the same sites over time, scientists can track changes in air quality and assess the effectiveness of environmental policies. Lichens are a powerful tool in our fight for clean air, offering a natural and cost-effective way to monitor the health of our planet.

How long can lichens live?

The lifespan of lichens can vary quite a bit; it all depends on the species and the environment. Climate plays a significant role, though, with lichens in mild climates living shorter lives and lichens in colder climates living longer lives.

Some lichen species, particularly those found in tropical and subtropical regions growing on leaves, have lifespans as short as one to two years. On the other end of the spectrum, lichens found in Antarctica, where the harsh environment slows down growth, have been estimated to be over 5,000 years old! In temperate zones, the lichens we encounter likely have lifespans ranging from a few decades to a few hundred years.

Usefulness of lichens

Besides being air quality monitors, lichens offer other benefits to humans and have a rich history of practical applications.

• Dyes: One traditional use of lichens is in dyeing textiles. Lichens are one of the few natural sources of the color purple, but they can also produce a wide range of other colors, including yellows, browns, reds, and blues. The process can be time-consuming, but the resulting dyes are beautiful and long-lasting. It’s important to note that, unlike mushrooms, harvesting lichens kills the organism. So, if you’re interested in trying lichen dyeing, it’s best to collect only what has already fallen to the ground.
• Fragrance: Lichens also play a role in the world of fragrance. Certain lichen species have been used in perfumes for centuries. Its their unique properties that contribute to the complexity and depth of certain perfumes.
• Medicines: Lichens have been used medicinally for thousands of years. Specifically, their extracts have been used in tinctures for a variety of ailments, though some have proven unreliable. Some lichens show promise for developing antibiotics, antifungals, and antivirals; however, large-scale cultivation is challenging due to their slow growth rates.

Lichens in the city

This post contains affiliate links — see my disclosure policy.

As we’ve already covered, lichens can be found in a surprising variety of locations, including bustling cities. Dr. Jessica Allen, the lichenologist I interviewed for the podcast episode this article is based on, authored the book “Urban Lichens: A Field Guide for Northeastern North America.”

It turns out that lichens in urban environments can differ from their rural counterparts. The stresses of city life, such as air pollution, can cause changes in lichen appearance. For example, the algal partner in a lichen may escape the fungal embrace and grow on the surface. These unique characteristics can make identification using traditional field guides difficult.

Dr. Allen’s book fills this gap by providing a resource specifically tailored to identifying lichens in urban areas. It offers an accessible guide for city dwellers who are curious about the hidden world of lichens thriving right under their noses. So next time you’re walking through a park or down a city street, take a closer look at the rocks, trees, and buildings around you. You might be surprised by the diversity of lichens calling the urban jungle home.

Busting lichen myths

Here are a couple of common myths Dr. Allen mentioned in our interview that she wants to dispel:

• Myth #1: Lichens only grow on the north side of trees. This is simply not true. Lichens can be found on all sides of trees and other surfaces.
• Myth #2: Lichens are harmful to trees. While lichens may grow on trees, they are not parasites. They do not harm the tree and can even provide some benefits, such as offering a degree of protection from harsh weather conditions.

Summary

• Lichens are a complex symbiotic partnership between a fungus and an algae or cyanobacteria.
• Beyond their main partnership, lichens often harbor a surprising array of bacteria, other fungi, and even tiny multicellular animals.
• Lichens are incredibly adaptable and can thrive in harsh environments, from city sidewalks to the frigid tundra.
• Lichens are a food source for a diverse range of herbivores, from insects to much larger grazers like caribou and reindeer.
• Lichens also serve as nesting material for birds and squirrels, and some insects use lichens for camouflage.
• Certain lichen species have a symbiotic relationship with cyanobacteria that helps fix nitrogen from the air, making it available for other organisms.
• In drier areas, lichens contribute to soil stability by forming a protective crust on the surface.
• Lichens can be surprisingly long-lived, with some specimens estimated to be over 5,000 years old.
• Lichens are sensitive to air pollution and can be used as bioindicators to monitor air quality.
• Lichens have a remarkable ability to tap into multiple nutrient sources, from the atmosphere to the substrate they grow on.
• Over the years, lichens have been useful in making dyes, fragrances, and medicines.

Explore lichens further

• At-home microbiology activities: Discovering Lichens (3 Hands-On Activities)
• Lichen Basics: Dr. Jessica Allen (podcast episode)
• Next Time You Go Hikin’ Look For A Lichen (article)
• Introduction to Lichens: Dr. Klara Scharnagl (podcast episode)