Lichens
Lichens are the organisms produced by the permanent association of algae and fungi. The algae
in lichen belongs to either cyanobacteria (Nostoc, Rivularia etc) or chlorophyceae (Cladophora,
Protococcus etc). Fungi in lichens belong to ascomycetes and basidiomycetes. About 400 genera
and 1600 species of lichen have been reported.
Habit and habitat
They are commonly found on the walls, house, trunks of trees, rock etc.
Structure
Body of lichen consists of thallus. The size of thallus varies from 1 mm to one meter diameter.
According to external morphology, lichens are divided into three types.
1. Crustose lichens: The thallus of lichens is closely attached to substratum. Therefore it
can’t be separated without damaging it. Eg: Graphis, Lecanora,dermatocarpon etc.
2. Foliose lichens: These have flat, leaf like, lobed thallus, attached to the substratum by
rhizoid. The lobes of thallus are with irregular margin. Eg: Peltigera, parmelia,physcia,Collema etc.
3. Fructicose lichens: They are branched, cylindrical or ribbon like thallus, which is
upright or pendulous. The thallus is attached to the substratum by its basal portion
composed by densely packed hyphae. Eg: Usnea, Evernia,cladoniaetc.
Reproduction of lichen
Lichen reproduces by asexual and sexual methods:
Asexual reproduction
It occurs by the following methods:
1. Fragmentation: In fragmentation methods, the lichen thallus breaks into small
fragments and each fragment gives rise to new thallus.
2. Soredia: These are special small bud-like out growths developed on the thallus. Each
soredium consists of few algal cells surrounded by fungal hyphae. In suitable
condition, soredia germinate to produce new thallus.
3. Isidia: They are small projections on the upper surface of the thallus. They consist of an
external cortical layer and an internal algal layer. When the thallua become dry they
break off and develop into new thallus.
Sexual reproduction
Sexual reproduction in lichens is performed by its fungal partner. Most of the fungal partners
are ascomycetes. So sexual reproduction takes place by formation of ascospore in asci.
Female reproductive organs is carpogonium and male reproductive organs are called
spermogonia which produce the spermatia.
Economic important of lichens
1. Pioneers of vegetation: crustose lichens aries first on the bare rocks. They secrete acids
and disintegrate rocks into soil particles, where moss and higher plants are established.
2. Food: some species of lichen are also used as food. Eg: Parmelia.
3. Medicines: some species of lichens are used in treatment of some disease.
i) Lobaria pulmonaria are used in lungs disease.
ii) Xanthoria sp are used in jaundice etc
4. Perfumes: Several species of lichens are used in preparation of cosmetic perfumes.
5. Bio-indicators of air pollution: Lichens grow in pollution free places. As the level of
pollution increase, their number decrease. By this trend, degree of air pollution can be
predicated.
6. Dyes: Lichens are used to manufacture high quality dyes of various colors. Litmus is also
obtained from lichens.
7. Forest fire: Dry thalli of lichens in forest from the thick mat on tree branches and easily
catch fire. So there is high risk of forest fire due to lichens.
8. Damaging buildings: Lichens can grow on the walls of buildings. As they secret acids,
they can damage the plasters and shining beauty of buildings.
9. Shading of leaf: lichens can grow on the plant leaves and block the sunlight, so that
photosynthesis of plant is badly affected.
Lichens are the organisms produced by the permanent association of algae and fungi. The algae
in lichen belongs to either cyanobacteria (Nostoc, Rivularia etc) or chlorophyceae (Cladophora,
Protococcus etc). Fungi in lichens belong to ascomycetes and basidiomycetes. About 400 genera
and 1600 species of lichen have been reported.
Habit and habitat
They are commonly found on the walls, house, trunks of trees, rock etc.
Structure
Body of lichen consists of thallus. The size of thallus varies from 1 mm to one meter diameter.
According to external morphology, lichens are divided into three types.
1. Crustose lichens: The thallus of lichens is closely attached to substratum. Therefore it
can’t be separated without damaging it. Eg: Graphis, Lecanora,dermatocarpon etc.
2. Foliose lichens: These have flat, leaf like, lobed thallus, attached to the substratum by
rhizoid. The lobes of thallus are with irregular margin. Eg: Peltigera, parmelia,physcia,Collema etc.
3. Fructicose lichens: They are branched, cylindrical or ribbon like thallus, which is
upright or pendulous. The thallus is attached to the substratum by its basal portion
composed by densely packed hyphae. Eg: Usnea, Evernia,cladoniaetc.
Reproduction of lichen
Lichen reproduces by asexual and sexual methods:
Asexual reproduction
It occurs by the following methods:
1. Fragmentation: In fragmentation methods, the lichen thallus breaks into small
fragments and each fragment gives rise to new thallus.
2. Soredia: These are special small bud-like out growths developed on the thallus. Each
soredium consists of few algal cells surrounded by fungal hyphae. In suitable
condition, soredia germinate to produce new thallus.
3. Isidia: They are small projections on the upper surface of the thallus. They consist of an
external cortical layer and an internal algal layer. When the thallua become dry they
break off and develop into new thallus.
Sexual reproduction
Sexual reproduction in lichens is performed by its fungal partner. Most of the fungal partners
are ascomycetes. So sexual reproduction takes place by formation of ascospore in asci.
Female reproductive organs is carpogonium and male reproductive organs are called
spermogonia which produce the spermatia.
Economic important of lichens
1. Pioneers of vegetation: crustose lichens aries first on the bare rocks. They secrete acids
and disintegrate rocks into soil particles, where moss and higher plants are established.
2. Food: some species of lichen are also used as food. Eg: Parmelia.
3. Medicines: some species of lichens are used in treatment of some disease.
i) Lobaria pulmonaria are used in lungs disease.
ii) Xanthoria sp are used in jaundice etc
4. Perfumes: Several species of lichens are used in preparation of cosmetic perfumes.
5. Bio-indicators of air pollution: Lichens grow in pollution free places. As the level of
pollution increase, their number decrease. By this trend, degree of air pollution can be
predicated.
6. Dyes: Lichens are used to manufacture high quality dyes of various colors. Litmus is also
obtained from lichens.
7. Forest fire: Dry thalli of lichens in forest from the thick mat on tree branches and easily
catch fire. So there is high risk of forest fire due to lichens.
8. Damaging buildings: Lichens can grow on the walls of buildings. As they secret acids,
they can damage the plasters and shining beauty of buildings.
9. Shading of leaf: lichens can grow on the plant leaves and block the sunlight, so that
photosynthesis of plant is badly affected.
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