Lichen: A very good example of symbiosis


Do you know what is lichen? In this article you will find a detail explanation of lichen. You will find nature and habitat of lichen. You will also find structure, classification and economic importance of lichens. To know more about lichen please read this article.

Introduction


Lichen is thallophytic, composite and symbiotic organism. Lichen is an association of algae and fungi. The fungi member is known as mycobiont and algae member is known as phycobiont. About 15000 species are included in this group.
Lichens are very good example of symbiosis where algae being autotrophic manufactures the food through photosynthesis and the fungi absorbs water and minerals from the substratum, as well as fungi provide rigidity to the thallus.
Lichens are placed in fungi group according to five kingdom classification .

Habitat


Lichens are grayish green or greenish, white, yellow, orange, brown, red and black in colour. Lichens can be observed on the old wall, rocks, stems and branches or shrubs and trees, logs of wood and on ground. Some of the lichens are very resistant and may survive for long periods of desiccation. Lichens are able to invade the bare rocks and make the environment suitable for other forms of life also. Lichens play an important role in xerophytic plant succession.

External structure and classification of Lichens


If the fungal member belongs to the class ascomyctes the lichen is classified as ascolichens and if fungal member belongs to bsidiomycetes the lichen is classified as basidiolichens. The lichens are of three types:

  1. Crustose lichens : Forming hard granular crusts, adhering to rocks and barks of trees. For examples, Graphis, Haematoma, etc.

  2. Foliose lichens : Forming flattened leaf like thalli with lobed margins. Foliose lichens adhere to rocks, old walls and trees trunks by delicate rhizoids called rhizines. For examples, Parmalia, Physcia, Peltigera, etc.

  3. Fructicose lichens : Forming much branched shrub like bodies and remaining attached to the substratum by their narrow basal portion. In some lichens the algal body remains scattered in the thallus, while in other they occur in one or two layers. For examples, Cladonia, Evernia, Usnea, etc.



Reproduction in Lichens


Lichens reproduce by following three methods:

  • Vegetative reproduction

  • Asexual reproduction

  • Sexual reproduction


Vegetative reproduction : Vegetative reproduction is a process in which new offspring produces through the body of single organism. The different types of vegetative reproduction takes place in lichens are by soredia, isidia and cephalodia.
Asexual reproduction :
Asexual reproduction takes place by the formation of spores formed by the fungal partner. Each spore on germination sends hyphae in all directions and spore comes in contact with the requisite alga, spore branches and covers up the algal cell. This combined body forms a lichen thallus. In many lichens, a flask shaped cavity called pycnidium is formed, from where spore like pycnidiospores develop and when they come in contact with the requisite alga, they form new thallus.
Sexual reproduction
Sexual reproduction takes place in certain ascolichens. The fruiting body is either a cup shaped apothecium or a flask shaped perithecium. Sex organs are well differentiated, the male is flask shaped chamber called spermogonium, within numerous, minute, non motile cellsa are formed. Female organ is called as carpogonium. Carpogonium consists of basal swollen portion called the ascogonium, and a upper tubular portion called the trichogyne. The male and female sex organs on maturation undergo the process of fusion. As a result of the fertilization and further growth the final product, i.e. the fruiting body is formed.

Useful activities of Lichens


The uses of Lichens are given below:

  • Some species of lichen are used as food by human beings and animals, E.g., Lecanora and Rocella are used by man and Cladonia rangifera forms the food of reindeer in Tundra region.

  • The lichens etch the rocks, through the both chemical and physical actions, there after the plants like mosses and grasses come in succession and utilize the first soil formed by lichens. So, are called soil builders.

  • Many useful medicines are obtained from lichen. E.g., Cladonia is used for making the drug of fever, Erwinia for making the medicine of cough and Peltigera for making the medicine of hydrophobia.

  • Some lichens are used in making perfume. E.g., Remalina, Lobaria.

  • Some species of Rocella and Lecanora yield colouring matter, which are used as dyes for colouring woolen and silk fabrics.

  • Some species of lichens are used for extracting minerals from rocks as lecanora is used for getting calcium oxalate.

  • Many organic acids are obtained from lichens. E.g., uramic acid is used for killing harmful bacteria present with antibiotic streptomycin.



Harmful activities of Lichens


Some harmful activities of lichen are as given below:

  • Many lichens produce skin diseases in human beings.

  • Lichens destroy the glass of window, wood and stones of the walls.

  • After drying lichens burn and produce fire for the forests, i.e., lichens are combustible.


So, dear friends, these are some important detail of Lichens. You can find this lichen at natural places and lichen is a good species to preserve in herbarium .


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