Lichens

There are a lot of things to like about lichens—they are colorful, grow on a variety of substrates, and have interesting shapes! Wildlife that use lichens for food include white-tailed deer, flying squirrels, and snails. Ruby-throated hummingbirds and blue-gray gnatcatchers camouflage their nests with shield lichens while Northern parula warblers weave strands of beard lichens into their nests hanging from conifer trees. As pioneers in the natural succession of an ecosystem, lichens break down rocks over time, creating soil for new plants.

A lichen is comprised of a fungus and green algae or a cyanobacteria (or all three) living together. This symbiotic relationship benefits the partners, as the fungus provides housing for the photosynthetic algae or cyanobacteria, which contribute food and nutrients for the fungus.

If you peered at lichen under a microscope, you would see that they are composed of an upper cortex layer of thick-walled cells packed closely together, covering a wider layer of loose fungal fibers called hyphae. The lower cortex layer seals the lichen body and attaches to rocks, wood, or another substrate. An even closer look would show there’s a lot going on inside this complex relationship. Trapped in the hyphae is a food-producing partner called the photobiont, which could be green algae or cyanobacteria. Just as a leaf uses energy from the sun, the photobiont uses photosynthesis to make food for the fungus. As a good roommate, the fungus protects this food supply, providing steady moisture and shielding the algae from too much sunlight.

The yellow map lichen is a slow grower at 0.09 mm per year while the common greenshield lichen spreads radially at 5 mm per year. The fastest may be the pelt lichens, which grow 20 mm per year!

Lichens are efficient collectors of airborne particles, but they have no filtering mechanism and cannot rid themselves of these compounds, which bio-accumulate. Certain species can live in dirty air from urban environments while a greater diversity exists in better air of wilderness areas, so lichens are valuable to science as bio-indicators of air quality.

As you venture out, it should be easy to find many reasons to like lichens!

What They Look Like and Where They Live

Lichens appear in three forms: crustose, foliose, and fruticose. Generally, they live in three places: on the ground, on rocks, and on trees.

Crustose means crust-like, appearing like dots or flakes that are flat and close together. The lower surface binds directly onto the surface. Fungi that form symbiosis with nitrogen-fixing cyanobacteria are evident in dark gray, brown, or black lichens.

Foliose forms resemble leafy growths divided by lobes. The lower cortex is often differently colored from the upper cortex. Some are raised above the substrate on short pegs, called rhizines, attaching to the surface.

Fruticose forms look like a fruiting body with shrubby growths or branches that may be erect, drooping, or curled. Good examples are pixie cup and British soldier lichens.

Grow dwellers choose soil, sand, decomposing downed logs, or stumps. They produce hyphae that bind soil particles together and add organic matter along with usable nitrogen to the soil. Grayish-green reindeer lichens reflect sunlight, thus cooling the soil beneath them while helping retain moisture.

Suitable locations include boulders, concrete, cliff rocks, gravestones, and even shingles. The orange elegant sunburst lichen thrives on exposed rocks along lakeshores, especially where gulls visit, as gull droppings provide nitrogen to the lichen.

Tree bark changes in texture and chemistry as it ages, becoming softer and oozing alkaline nitrogenous compounds, allowing lichens to grow.


There are a lot of things to like about lichens—they are colorful, grow on a variety of substrates, and have interesting shapes! Wildlife that use lichens for food include white-tailed deer, flying squirrels, and snails. Ruby-throated hummingbirds and blue-gray gnatcatchers camouflage their nests with shield lichens while Northern parula warblers weave strands of beard lichens into their nests hanging from conifer trees. As pioneers in the natural succession of an ecosystem, lichens break down rocks over time, creating soil for new plants.

A lichen is comprised of a fungus and green algae or a cyanobacteria (or all three) living together. This symbiotic relationship benefits the partners, as the fungus provides housing for the photosynthetic algae or cyanobacteria, which contribute food and nutrients for the fungus.

If you peered at lichen under a microscope, you would see that they are composed of an upper cortex layer of thick-walled cells packed closely together, covering a wider layer of loose fungal fibers called hyphae. The lower cortex layer seals the lichen body and attaches to rocks, wood, or another substrate. An even closer look would show there’s a lot going on inside this complex relationship. Trapped in the hyphae is a food-producing partner called the photobiont, which could be green algae or cyanobacteria. Just as a leaf uses energy from the sun, the photobiont uses photosynthesis to make food for the fungus. As a good roommate, the fungus protects this food supply, providing steady moisture and shielding the algae from too much sunlight.

The yellow map lichen is a slow grower at 0.09 mm per year while the common greenshield lichen spreads radially at 5 mm per year. The fastest may be the pelt lichens, which grow 20 mm per year!

Lichens are efficient collectors of airborne particles, but they have no filtering mechanism and cannot rid themselves of these compounds, which bio-accumulate. Certain species can live in dirty air from urban environments while a greater diversity exists in better air of wilderness areas, so lichens are valuable to science as bio-indicators of air quality.

As you venture out, it should be easy to find many reasons to like lichens!

What They Look Like and Where They Live

Lichens appear in three forms: crustose, foliose, and fruticose. Generally, they live in three places: on the ground, on rocks, and on trees.

Crustose means crust-like, appearing like dots or flakes that are flat and close together. The lower surface binds directly onto the surface. Fungi that form symbiosis with nitrogen-fixing cyanobacteria are evident in dark gray, brown, or black lichens.

Foliose forms resemble leafy growths divided by lobes. The lower cortex is often differently colored from the upper cortex. Some are raised above the substrate on short pegs, called rhizines, attaching to the surface.

Fruticose forms look like a fruiting body with shrubby growths or branches that may be erect, drooping, or curled. Good examples are pixie cup and British soldier lichens.

Grow dwellers choose soil, sand, decomposing downed logs, or stumps. They produce hyphae that bind soil particles together and add organic matter along with usable nitrogen to the soil. Grayish-green reindeer lichens reflect sunlight, thus cooling the soil beneath them while helping retain moisture.

Suitable locations include boulders, concrete, cliff rocks, gravestones, and even shingles. The orange elegant sunburst lichen thrives on exposed rocks along lakeshores, especially where gulls visit, as gull droppings provide nitrogen to the lichen.

Tree bark changes in texture and chemistry as it ages, becoming softer and oozing alkaline nitrogenous compounds, allowing lichens to grow.

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