What is Lichen?
There once was a little patch of fungi that took a lichen (pronounced liken) to a beautiful batch of algae. This terrible joke has helped me remember what two organisms make up lichen. While you're probably not rolling on the floor laughing, hopefully it'll help you remember, too. Lichen, if you haven't gathered already, is formed by the mutualistic relationship between a fungus and an alga. Mutualism is a type of relationship where both organisms benefit from being together. So, the algae help the fungi and the fungi help the algae. Before we go on, something to note (in case you're asking yourself what in the world an alga is):
- Algae is plural and alga is singular.
- Fungi is plural and fungus is singular.
You're probably wondering how the algae benefits the fungus and vise versa. The fungi provide the home, and the algae provide the food. For example, the fungi hold in moisture, and provide a structure where the algae can grow. In turn, the algae use sunlight (and photosynthesis) to produce food for the fungi.
How does it look when the fungi takes a lichen to the algae? Don't worry, I'll stop with the bad joke soon. There are thousands of types of lichen, but just a handful of lichen shapes. We will focus on three of these: crustose, fruticose and foliose. Let's check out each shape.
The first shape is crustose, which is lichen that sticks closely to whatever it's growing on. Like its name suggests, it is crusty and even forms a crust on its growing surface (can include rocks, trees or even dirt). This crust can be difficult to remove.
The next type, fruticose is like a little branching shrub, kind of like a miniature leafless tree. It looks somewhat like a bushy coral and grows on rocks, trees and soils. While fruticose does not sound like shrub, the Latin origin of the word actually translates into bush or shrub, so the name makes sense.
The next group is called foliose, which has a leafy shape and can be easily removed from its growing surface. They get their name because they look like foliage (plant leaves).
We know that lichen is the result of a mutualistic relationship between fungi and algae. And we know a few of the shapes of lichen, but what other characteristics does this diverse group share?
Different varieties of lichen can come in a wide range of colors like red, orange, yellow, gray and green. Typically, lichen is slow growing and most can grow on surfaces that seem really inhospitable, like rocks, tree bark and soils. Because they can grow in these challenging places, they are often the first organisms to grow in an area that has been disturbed. For example, in regions where glaciers are retreating, take a look at the rocks and you might see some lichen growing in an otherwise barren landscape. They are also a food source for many animals including caribou.
Many lichens deal with harsh environmental conditions, like drought, heat or cold by going dormant. While they are extraordinarily tough, some are sensitive to pollution, mainly sulfur dioxide from the burning of coal. In Siberia, the number of lichen types has gone from 50 to three, and England and Whales have lost countless types of lichen due to air pollution.
Lichen is the perfect example of teamwork. Remember, lichen is the result of a mutualistic relationship between algae and fungi where the algae provides the food and the fungi provide a structure. A mutualistic relationship is where both organisms benefit from living together. There are thousands of types of lichen, but there are only a handful of lichen shapes. We focused on three. Review the table to refresh your memory.
|Crustose||Crusty||Forms a crust over its growing surface.|
|Fruticose||Shrubby||Forms leafless, coral/shrub-like structures.|
|Foliose||Leafy||Forms a leaf-like structure.|
Finally, lichen grows in harsh areas (rocks, tree bark and soil), and is a food source to some animals like caribou. They can withstand many challenges, but the Achilles heal for many is air pollution, which has already wiped out many varieties around the world.
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Lichen: Crossword Puzzle
In this activity, you'll check your knowledge regarding the types and characteristics of a lichen.
Complete the crossword by filling in a word that fits each of the given clues. For this activity, you'll need a printer to reproduce the following page. With a pencil and an eraser, neatly write your answers in the boxes provided.
2. __________ are a group of living organisms that have mutual associations with algae, bacteria, and plants.
3. A __________ is a complex organism with a plant-like appearance that can conduct photosynthesis.
6. Lichens are extremely sensitive to sulfur dioxide, which is a by-product of atmospheric __________.
8. __________ are a diverse group of aquatic organisms with the ability to produce their food, a process known as photosynthesis.
10. Mutualism is an interaction between two different species in which each organism __________.
1. Due to pollution, the species of lichens in __________ have dwindled in numbers.
4. __________ strongly adheres to any surface, such as on rocks and tree barks, and is well adapted to dry climates.
5. A fruticose lichen is identified by its __________-like shrubby or bushy growth structure.
7. __________ serves as a food source for many animals and are characterized by their flattened, leafy appearance.
9. __________ are mammals that live in the northern regions of Europe, feeding on plants and lichen to survive.
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