What is Lichen Definition Structure and Types
Lichens are considered plant-like organisms that show symbiotic association with algae, till now there are 15,000 species of lichen. They mainly show symbiotic association with green algae or cyanobacteria and fungi (mostly ascomycetes and basidiomycetes). They are found all across the world depending on the condition of the environment. They are majorly found in colony form, like on the tree bark, exposed rock, and as a part of biological soil crust.
Lichens are also used as human beings as a source of food along with medicine extraction and dye. They are also considered a major source of food for reindeer that roam the far northern ranges.
Classification of Lichen
Lichens are classified into various types based on different factors. Some of the important types of classification of lichens are listed below
A. Based on their Growth -
Based on the growth of lichens, there are three types, they are
Crustose Lichens These lichens are thin, flat and don't have any distinct lobes. They are majorly found on the stones, rocks, barks and the trunk of trees. Some of the common examples of crustose lichens are Haematomma puniceum and Graphic scripta.
Foliose Lichens They are considered as one of the most attractive lichens and they are of flat shaped, broad, smooth and leaf-like structures, which often resemble crinkled and twisted leaves. They are generally attached with rocks and twigs with the help of rhizoids Some of the common examples of foliose are Cetraria, Cluiudhuria, Parmelia and Xanthoria
Fruticose Lichens These types of lichens are considered as one of the most important types of lichens and they are of thin nature and are freely branched. They are mainly grown on the branches of trees, foliage and rocks. Some of the common examples of fruticose lichens are Cladonia, Ramalina and Usnea.
B. Based on their Habitat -
Based on the nature of habitat lichen are classified into different types, they are:
Lignicolous: their presence is mainly on the wood.
Corticolous: Their presence is majorly on the bark of trees.
Saxicolous: Their presence is majorly on the stones or rocks.
Marine: They are mainly found on the siliceous rocks, near the shores of the sea.
Freshwater: These types of lichens are found growing on the hard siliceous rocks, especially around the freshwater.
Terricolous: They mainly grow on the soil and because of this reason they are called terrestrial lichens.
C. Based on their Internal Structure -
On the basis of internal structure lichens are classified into two types
Heteromerous lichens
Homoiomerous lichens.
D. On the Basis of their Fungal Partner -
Ascolichens
Basidiolichens
Hymenolichens
Important Role of Lichens
Lichens are considered to be important in terms of economic and environmental factors. Some of the important roles of lichens are discussed below:
Some species of lichen play a crucial role in the conversion of rocks into soil, as they are helpful in soil formation and also improve the quality of the soil by enriching important nutrients which are helpful in plant growth.
They also play an important role in the nitrogen cycle as they help in fixing nitrogen from the atmosphere.
They are also considered to be an important source of food all over the world for human beings. Example Iceland miss is known to be an important source of food for Northern Europe and American continents.
With the help of lichens, Petrologists and Geologists are able to study and calculate the age.
They are also used as an important source of colouring agents and dyes. They are known to be good sources of natural dyes. For example, pH indicator is extracted from the lichens.
They are also helpful in the biodegradation of polyester, lead, copper, radionuclides and other pollutants polluting the planet earth.
They are also used in pharmaceutical industries and along with that, they are also helpful in making cosmetic products.
They are helpful in treating various types of skin-related disease like rashes.
Few species of lichens are also used in the degradation process of various pathogens and resources which lead to dangerous infectious disease in the human body and in plants also.
They are an important source of food for aquatic animals.
FAQs on Lichen Structure Functions and Classification
1. What is lichen?
A lichen is a symbiotic association between a fungus and a photosynthetic partner such as an alga or cyanobacterium. The fungal partner (mycobiont) provides structure, protection, and absorbs water and minerals, while the photosynthetic partner (photobiont) produces food through photosynthesis. This mutualistic relationship allows lichens to survive in extreme environments like rocks, tree bark, and arctic tundra.
2. What are the components of lichen?
The main components of a lichen are a fungal partner and a photosynthetic partner. These include:
- Mycobiont: The fungal component that forms most of the lichen body and provides protection.
- Photobiont: The algal or cyanobacterial component that performs photosynthesis.
- Thallus: The body of the lichen formed by the association of both partners.
3. What are the types of lichens?
Lichens are classified into three main types based on their growth form: crustose, foliose, and fruticose.
- Crustose lichens: Form a thin crust tightly attached to surfaces like rocks.
- Foliose lichens: Have a leaf-like structure loosely attached to the substrate.
- Fruticose lichens: Appear bushy or shrubby and may hang from branches.
4. How do lichens reproduce?
Lichens reproduce through both asexual and sexual methods, depending mainly on the fungal partner.
- Asexual reproduction: Occurs through structures like soredia and isidia, which contain both fungal and algal cells.
- Sexual reproduction: Involves fungal spores produced in fruiting bodies such as apothecia, but the new fungus must find a compatible algal partner.
5. Where do lichens grow?
Lichens grow in diverse habitats ranging from arctic tundra to deserts and tropical forests. They commonly grow on:
- Rocks (saxicolous lichens)
- Tree bark (corticolous lichens)
- Soil (terricolous lichens)
- Old walls and rooftops
6. Why are lichens important in the ecosystem?
Lichens are important because they act as pioneer species, contribute to soil formation, and serve as bioindicators of air quality. Their ecological roles include:
- Weathering rocks and initiating soil formation.
- Providing food for animals like reindeer.
- Acting as bioindicators since they are sensitive to air pollution.
7. What is the structure of a lichen thallus?
The thallus of a lichen is a layered structure formed by fungal and algal cells working together. A typical thallus includes:
- Upper cortex: Protective outer fungal layer.
- Algal layer: Contains photosynthetic cells.
- Medulla: Loosely arranged fungal hyphae for storage and gas exchange.
- Lower cortex (in some lichens): Helps in attachment.
8. What is the difference between lichen and moss?
The main difference between lichen and moss is that lichen is a symbiotic association, while moss is a simple non-vascular plant.
- Lichen: Combination of fungus and alga/cyanobacterium.
- Moss: A bryophyte with stem-like and leaf-like structures.
- Lichens absorb nutrients from air, while mosses absorb from soil and water.
9. Can lichens survive in extreme environments?
Yes, lichens can survive in extreme environments due to their unique symbiotic structure and slow metabolism. They can tolerate:
- Extreme cold in polar regions.
- High heat and drought in deserts.
- Low nutrient availability on bare rocks.
10. What is the role of cyanobacteria in lichens?
In some lichens, cyanobacteria act as the photosynthetic partner and can fix atmospheric nitrogen. Their roles include:
- Performing photosynthesis to produce carbohydrates.
- Carrying out nitrogen fixation, converting atmospheric nitrogen into usable forms.
