Lichen

Lichens are not plants.

They are two living things joined together. One part is a tiny life that makes food. The other part is a fungus. The fungus acts like a skin to keep the first part safe.

Lichens can grow in many shapes. Some look like flat leaves.

Others look like tiny shrubs or even powder. Some grow very flat, like a coat of paint.

They come in many colors. You might see red, orange, or yellow.

Their color can change when they get wet. They can grow on rocks, trees, or even bones.

Lichens are very strong. They can live in hot deserts or cold places. Some can even grow inside solid rock. They are very old living things.

Lichens are not plants. They are a team of living things. A lichen is a colony of algae or bacteria living with a fungus. This partnership is called symbiosis. This means the two parts live together in a way that helps both.

The fungus is called a mycobiont. It makes up most of the lichen body. The body of the lichen is called a thallus. The fungus provides a skin called a cortex. This skin protects the lichen from too much sun. It also keeps other tiny things out.

The other part is the photobiont. This is the part that makes food. It uses light to make power through photosynthesis. Lichens can grow in many shapes. Some are fruticose, which means they look like tiny shrubs. Others are foliose, which means they look like flat leaves.

Some lichens are crustose. These grow very flat like paint on a rock. Lichens can live in many places. They grow on trees, rocks, and even bones. They can survive in hot deserts or cold arctic areas. Some can even grow inside solid rock.

Lichens are amazing living things that act like miniature ecosystems. They are not plants, even though they can look like them. Instead, a lichen is a hybrid colony. It is made of a fungus and a partner like algae or cyanobacteria. This partnership is called symbiosis. This means the different living things live together in a way that helps each other.

These tiny worlds are very important for nature. They help move nutrients around and provide food for animals like reindeer and mites.

How does this team work together? The fungus is called the mycobiont. It makes up most of the lichen's body, which is called a thallus. The fungus creates a protective skin called a cortex. This skin keeps out other organisms and blocks too much sunlight. Inside, the photobiont lives. The photobiont is the partner that makes food. It uses photosynthesis to turn light into energy.

The fungus provides a home, and the photobiont provides the energy. This way of working allows them to thrive in many places.

Scientists have studied these unique lifeforms for a long time. The word lichen comes from the Greek word for "licker." This might be because some lichens look like they could be licked. Lichens are also very old. Some are among the oldest living things on Earth. Because they grow very slowly and steadily, people use them to study history. This method is called lichenometry. It helps scientists date events by looking at how much a lichen has grown.

There are about 20,000 known species of lichens. They come in many different shapes, which is called morphology. Some are fruticose, which means they look like tiny, leafless shrubs. Others are foliose, which means they have flat, leaf-like parts. Some are crustose and grow tightly like a coat of paint on a rock.

You can find them in almost any environment. They live in hot deserts, cold arctic tundras, and even inside solid rock. They can grow on trees, walls, gravestones, and even bones.

Lichens are a great example of how different things can work as one. You might see them on a tree in your backyard. They might look like moss, but they are not related to moss at all. They can even grow on top of other lichens.

Their colors can change, too. A lichen might look gray when it is dry. When it rains, it might turn bright green or olive. This happens because the skin becomes clear when it is wet. This lets the green parts inside show through more easily.

A lichen is not a single organism, but a hybrid colony. It is a symbiotic partnership between a fungus and a photosynthetic partner. This partner is usually a green alga or a cyanobacterium. In biology, this relationship is called mutualism because both sides benefit. The fungus provides structure and protection. The photosynthetic partner, called a photobiont, produces energy through photosynthesis.

Because they function as one unit, lichens have properties different from their individual parts. They are essential to many ecosystems as nutrient cyclers and food sources. Many animals, including reindeer, gastropods, and mites, rely on them for survival.

The internal structure of a lichen is highly organized. The main body of the lichen is called the thallus. This thallus is made of fungal filaments known as hyphae. These hyphae branch and rejoin to create a mesh through a process called anastomosis.

Most lichens have a protective outer layer called a cortex. The cortex is made of densely packed, tightly woven hyphae. This layer acts like a skin to block excessive sunlight and keep out other organisms. Below the cortex lies the photobiont layer. This is where the algae or cyanobacteria live within less dense fungal filaments. Some lichens also have a lower cortex or anchoring structures called rhizines to attach to their substrate.

Lichens display a wide variety of growth forms, which scientists call morphology. These forms are grouped by the type of thallus they possess. Fruticose lichens grow like tiny, three-dimensional, leafless shrubs. Foliose lichens are flat and have leaf-like lobes.

Crustose lichens are crust-like and adhere very tightly to surfaces like a coat of paint. Some crustose lichens become "rimose," meaning they crack into small islands called areolas as they age. There are also squamulose lichens, which consist of small scales. Other forms include powdery leprose lichens, jelly-like gelatinous lichens, and even stringy filamentous types. Lichens that are bush-like or leafy are called macrolichens, while all others are microlichens.

Coloration in lichens is often determined by the photobiont or special pigments. Many lichens appear bright green or olive when they are wet. This happens because moisture makes the cortex more transparent, exposing the green cells below. When dry, they often appear gray, brown, or black.

Some lichens produce special pigments like yellow usnic acid. These pigments create vibrant reds, oranges, and yellows, which are common in dry habitats. Because color is so consistent, scientists use it to help identify different species. The visual landscape of places like Yosemite National Park can be transformed by these colorful colonies.

Lichens are incredibly resilient and can inhabit extreme environments. They grow from sea level to high alpine elevations. They can survive in arctic tundras, hot deserts, and even on toxic slag heaps. Some species are endolithic, meaning they live inside the tiny grains of solid rock.

They can grow on almost any substrate, including bark, stones, gravestones, roofs, and even bones. Because they grow so slowly and steadily, they are useful for dating environmental changes. This scientific method is known as lichenometry. It allows researchers to use the size of a lichen to estimate the age of a surface.

There are approximately 20,000 known species of lichens. Some are among the oldest living things on Earth due to their long life spans. While many lichens reproduce sexually using disc-like structures called apothecia, some have lost this ability.

Despite this, they continue to form new species. Lichens are considered a keystone species in many habitats. They provide critical support for trees and birds and help form biological soil crusts. They are often the very first living things to colonize fresh rock after a landslide.

Beyond their individual biology, lichens represent complex, self-contained miniature ecosystems. The interaction between the mycobiont (the fungus) and the photobiont (the algae or bacteria) can involve many other microorganisms. This creates a functioning system that may evolve into even more complex composite organisms.

By studying lichens, scientists gain insight into symbiosis, nutrient cycling, and the history of our planet's surfaces.