Lichens: Definition, Types & Importance

While travelling in the forest, on a rainy day, you must have noticed some patches on the tree trunk, rocks, etc. They are called Lichens. Lichens can be found in many colours, sizes, and forms that grow in less polluted areas. In this article, we will know about the different types of lichens and their economic importance.

Lichens Definition

Lichens are symbiotic associations between algae and fungi. The algal component (autotrophic) is called phycobiont and the fungal component (heterotrophic) is called mycobiont.

Lichens Habitat

Lichens are found in less polluted areas. They grow on the barren rock, wood log, tree trunk, soil, abandoned walls, etc. Some of them are found in aquatic habitats. Lichens can grow from sea level to high alpine elevations and can grow on almost any surface and in many environmental conditions.

Depending on the habitat, some terms are used to describe these lichens:

Lichens Types or Morphology

Lichens vary in colour like orange, brown, dark brown, grey, yellowish-green, etc. Based on their morphology, lichens can be of various types:

Crustose: These lichens are crust-like, closely attached to the substratum, e.g., Graphis, Lecanora.

Leprose: These are like minute scales attached superficially to the substratum, e.g., Lepraria.

Foliose: These are like twisted and wrinkled leaves, e.g., Parmelia, Physcia.

Fruticose: These are branched, erect with bushy appearance, e.g., Evernia, Ramalina, Usnea.

Filamentous: These lichens consist of chains of algal cells wrapped around by fungal hyphae, e.g., Racodium.

Lichens Internal Structure

1. The mycobiont constitutes the major part of the lichen body and only \(5\% \) part is made up of phycobiont.
2. The body is divided into the upper cortex, algal zone (gonidial layer), middle medulla, lower cortex and rhizines.
3. Only the algal zone contains photosynthetic partners.
4. In about \(98\% \) of lichens, the fungal partner belongs to Ascomycetes. In the rest, the fungal partner belongs to Basidiomycetes and Deuteromycetes.

Lichens Reproduction

1. Lichens may reproduce vegetatively or sexually.
2. They reproduce vegetatively by fragmentation, death, and decay, etc.
   • a. Dry lichens are brittle and small portions of thallus break away from the main thallus.
   • b. These broken portions are carried away by air which develops into new lichen.
3. Soredia are typical minute, rounded structures forming a powdery granule on the surface of lichen thallus.
   • a. They have few algal cells surrounded by fungal hyphae.They serve as vegetative propagules. They are found in Ramalina, Evernia. 
4. Isidia are coral-like structures or outgrowths on the upper surface of the margin of lobes of many lichens.
   • a. They also act as vegetative propagules.
5. Pycniospores or Pycnidiospores, which are borne in Pycnidium, a flask-shaped structure opening through the pores called ostioles, are the common asexual spores of lichens.
6. They reproduce sexually in the following ways:
   • a. Formation of the ascomycetous fruiting body.
   • b. Formation of basidiocarp.
7. Sexual reproduction is not considered a common method of reproduction to form a new lichen.
8. However, the sexual reproduction of lichens is similar to that of the fungi associated with it.

Economic Importance of Lichens

Some of the important uses of lichens are as follows:

1. Orchin dye is obtained from Roccella tinctoria.
2. Litmus is obtained from Rochella montagnei.
3. Cladonia rangiferina (Reindeer moss) is an edible and good source of antibiotics.
4. Ramalina, Evernia are used in perfume industries.
5. Lichens are air-pollution indicators. They do not grow where there is specifically \({\text{S}}{{\text{O}}_{\text{2}}}\) pollution.
6. Many lichens are useful in producing medicines, for e.g., Usnea and Cladonia.
7. They are used in tanning leather, for e.g., Lobaria pulmonaria.
8. Some lichens like Usnea are used in the brewing industry.

Do you know?

1. Litmus was obtained from the lichen Roccella montaigne.
2. Lichens are the best indicators of pollution. They do not grow in polluted environments.
3. Lichens help in understanding the process of biological succession by the ecologists. They are the pioneers of succession in xerosere.

Summary

Lichens are a symbiotic association between phycobiont and mycobionts. The algal partner performs the photosynthesis and the fungal partner provides shelter and is engaged in reproduction. Lichens may reproduce vegetatively or sexually. They grow in the least polluted area and are considered a good pollution indicator. Various lichens are useful in producing medicines. Lichens also help in understanding the process of biological succession by the ecologists.

Frequently Asked Questions (FAQs) on Lichens

Q.1. What are the three types of lichens?
Ans: The three types of lichens are crustose, foliose, and fruticose.

Q.2. What exactly is lichen?
Ans: Lichens are symbiotic associations between algae and fungi.

Q.3. Are lichens harmful to humans?
Ans: Yes, some lichens are harmful to humans because they contain certain toxic chemicals like vulpinic acid which are released into the air and water that are poisonous. 

Q.4. Where is a lichen found?
Ans: They grow on the barren rock, wood log, tree trunk, soil, abandoned walls, etc. Some of them are found in aquatic habitats. 

Q.5. Are lichens ecologically important?
Ans: Yes, lichens are ecologically very important from two different perspectives. Lichens are very good pollution indicators and they are the pioneer community to initiate ecological succession.

Q.6. Are lichens fragile?
Ans: Yes, lichens are fragile when they become completely dry and brittle due to the loss of moisture.

Now that you are provided with all the necessary information about Lichens and we hope this detailed article is helpful to you. If you have any questions on Lichens, feel to post your comments in the comment box below and we will get back to you as soon as possible.