[Biology Class Notes] on Lichen Pdf for EXAM

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:

1. Lignicolous: their presence is mainly on the wood. 

2. Corticolous: Their presence is majorly on the bark of trees.  

3. Saxicolous: Their presence is majorly on the stones or rocks. 

4. Marine: They are mainly found on the siliceous rocks, near the shores of the sea.   

5. Freshwater:  These types of lichens are found growing on the hard siliceous rocks, especially around the freshwater.

6. 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 

1. Heteromerous lichens

2. Homoiomerous lichens.

D. On the Basis of their Fungal Partner –

1. Ascolichens

2. Basidiolichens

3. 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:

1. 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. 

2. They also play an important role in the nitrogen cycle as they help in fixing nitrogen from the atmosphere. 

3. 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. 

4. With the help of lichens, Petrologists and Geologists are able to study and calculate the age.

5. 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. 

6. They are also helpful in the biodegradation of polyester, lead, copper, radionuclides and other pollutants polluting the planet earth.

7. They are also used in pharmaceutical industries and along with that, they are also helpful in making cosmetic products.

8. They are helpful in treating various types of skin-related disease like rashes. 

9. 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. 

10. They are an important source of food for aquatic animals.