Lichen: Environmental Importance, Symbiosis & Facts

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll be learning about the tiny world of lichens. By the end of this lesson, you'll be able to explain what lichens are and why they are important for both humans and our greater ecosystem.

What Are Lichens?

Picture hiking in a forest. As you follow the dirt path through the trees, fallen logs and large boulders come into view. As you get closer, you notice a light green coating on the rocks. The beautiful color isn't paint, but rather it's a living thing called a lichen. Lichens are actually composed of two organisms living together, fungi and algae or cyanobacteria. Lichens can appear as crusty or leafy coatings on the ground, rocks, logs, or other moist areas.

Lichens are a diverse group with over 15,000 species documented. So, it's no surprise that they come in a wide variety of colors and shapes, from pale blue to bright red. Some lichens are tightly bound to the surface they grow on, forming a crusty covering. Others are larger, with fluffy, leaf-life attachments.

Lichen grows in all colors and shapes on a variety of surfaces


For many years, people used to think lichens were one species. However, with the advent of microscopes, scientists were able to see that lichens are actually two or more organisms working together in a process called symbiosis. Lichens are made of fungi, usually ascomycetes and basidiomycetes. Fungi are heterotrophs, meaning they have to ingest their food. The fungi in lichens have found a way around getting their own food though. They live in symbiosis with cyanobacteria or algae that are able to make their own food through photosynthesis.

Algae and cyanobacteria normally need a moist environment to survive in and thus typically aren't found on land away from water. But, the fungi can absorb water vapor to keep their partner moist and provide shade from punishing UV radiation. The cyanobacteria or algae, on the other hand, use water and sunlight to make sugars that the fungus needs to survive.


With such tiny organisms and sparse ground cover, you might still be wondering why we should care about lichens. It turns out lichens are incredibly important for establishing new ecosystems, providing food for animals, preventing soil erosion, and for monitoring pollution levels in our environment.

Primary Succession

Millions of years ago, volcanos covered the Earth. Islands were forged out of hot, liquid rock from eruptions. Today, many of these are lush, tropical islands filled with unique plants and animals. How did black, barren rock turn into the jungles we see today? The answer is called primary succession, and lichens play a key role in it. During primary succession, forests arise from the barren rock with no prior life, such as after a volcano eruption.

The first colonizers of the rock are often lichens. Lichens are highly versatile and can extend root-like projections called rhizines into the rock to anchor themselves. The fungi are hardy and can withstand the dry, hot, rocky environment that is present in early stages of primary succession. The algae or cyanobacteria are sheltered and are able to make food for the fungi. Over time, the lichens break down the rock they are growing on, producing sediment and new layers of soil for other plants to take root in.

Lichens are the first colonizers on barren rock
lichen on rock

Without lichens, colonizing these habitats would be nearly impossible. Other plants that arise later in succession depend on the lichens to break down the rock, freeing nutrients and soil needed for growth.

Food Source

At this point, lichens might be sounding much more interesting but probably still not so appetizing. Although lichens aren't on our menu, they are a primary food source for many animals. Caribou, also known as reindeer, live in the cold tundra and Arctic circle of the north. During winter, food becomes incredibly scarce in this already hostile environment. However, lichens are quite hardy and can withstand even the toughest environmental conditions and become a main food of caribou during their winter journey. Some Native Americans even ate lichens as food in times of hardship as well. But, don't get any ideas about your dinner plans; many lichens are poisonous and thus should not be eaten in the wild.

Caribou graze on lichen in the tundra

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