Lichen

 

Lichen (Dual organism)

Lichens are the symbiotic association of algae and fungi. Algal partners of lichen are called phycobiont and fungal partners of lichen are called mycobiont. Fungal partners provide shelter and protection to algal partners. Common fungal partners are the members of Ascomycetes, Basidiomycetes , etc. but common algal partners are blue green like algae Nostoc, Anabaena and some green algae.

Fungal partners are heterotrophic in nutrition so can not synthesize their own food material but algal partners are photoautotrophic in nutrition. Hyphae of fungi absorbs H2O and minerals from subtractum but algal partners synthesize their own food material by utilizing CO2 and H2O in presence of sunlight. This prepared food is consumed by both the partners. In lichen reproduction is fungi type.

Distribution

 Lichen include 400 genera and 1600 identical species. They are abundantly found in dry habitats of tropical as well as sub tropical regions. Thallus is green-greenish or sometimes blue grey in color. On the basis of their external morphology, internal structure and portional of apothecia, they are divided into 3 types:

1. Crustose Lichen
2. Foliose Lichen
3. Fruticose Lichen 

1. Crustose Lichen

These lichen bear small and thin thallus which is seen crust like in structure and found attached on substratum. Here, the lower portion of thallus is directly attached to the substratum and it doesn't bear rhizinae for absorption and fixation. On the upper surface of thallus few cup shaped apothecia are found in which production of spores occurs. E.g : Graphics, Lecanora, Lecidea, etc.

  2. Foliose Lichen

These lichens are small and dry in structure. They are found loosely attached on substratum with the help of rhizinate. On the upper surface they bear a small cup shaped structure called apothecia. Internally they are heteromerous types. E.g Physcia, Parmelia, Peltigera, etc. 

 3. Fruticose Lichen

They are branched or unbranched thalloid structures and are generally found hanging on the branches of trees. They are attached to the substratum with the help of a basal disk. At the tip of branches apothecia are found. Internally they are heteromerous .E.g. Usnea, Ramalina, etc.

Economic importance of Lichen:

 There are so many beneficial activities of lichen and are very much important to human beings and other organisms in different aspects. They are discussed below:

• Lichen as bio-indicator of pollution : Lichen are good biological indicators of pollution. They can’t survive in highly polluted areas especially of SO2 pollution. Pollutants can easily enter inside thallus but they can’t release out from thallus. When accumulation of pollutants become maximum, death of thallus occurs. In this way we can determine the pollution by sampling the frequency of dead species of Lichens. 
• Lichen as pioneer vegetation in Succession : Crustose lichen can grow on barren rock. They secrete sudden organic acid which causes the breaking down of a rock into the soil particle and after the death of lichen amount of organic matter is increased in soil and foliose lichen develop on such place. Gradually they are replaced by fern plants and are replaced by herbaceous and shurby angiosperm.
• . Lichen as food : Some members of lichen like Cladonia, Parmelia umbilicaria are used for preparation of different types of food. Parmelia perlata is used for making delicious soup.
•  Lichen as medicine : Usnea is used for extraction of usnic acid which is used for making ointment used in infection , burn etc. Parmelia perlata is used for the treatment of snake and scorpion bite. 
•  Lichen as cosmetics : Some lichens are used for the production of different cosmetics. soaps are prepared from the Ramalina species.

Hope this will help you a lot.

For more, be in touch with eduguidenep.blogspot.com