Lichen

Lichens are the symbiotic association of algal and fungal part so, are closely associated with each other.so, that they provide single body structure. Algal part is known as phycobiont. It prepares food for itself and for the fungal part also. Fungal part is known as mycobiont. It absorbs water and minerals and provides protection to the thallus. Thallus structure is irregular and variously coloured like black, brown, white, red, orange.

Occurrence

They have a wide range of occurrence. They are found in a various type of habitat like a tree trunk, branches of trees, fallen leaves, wall and leaf on the surface of a rock.

Types of Lichens

There are various types of lichens. They are as follows;

Crustose lichens

Crustose lichens are very thin and closely attached to substratum so, it is difficult to separate it from the substratum. They bear fruiting body, apothecia on the upper surface. Eg; Lecanora, Graphis. Lecanora, Graphis.

Foliose Lichens

Foliose lichens are much branched and folded and it forms leaf-like appearance. They are attached to substratum with the help of rhizine.

Fruticose lichens

They are much branched, erect, and pendulous structure. They bear fructose body at the tip of branches. Eg; Clodonia unsea

Economic Importance of Lichen

• It is the biological indicator of air pollution.
• It is the pioneer species of ecological succession.
• Species of Lecavora Parmelia can be used as food in different parts of the world.
• Parmelia perlatais used in snake bite.
• Species of Evernia, Roccella, Parmelia Racella montaignei is used in preparation of litmus paper.
• Species of Parmelia, Evernia, Evernia purnastris is mostly used in perfume making.

Reproduction in Lichens

Reproduction in lichen takes place both by sexual and asexual reproduction. Asexual reproduction takes place by fragmentation, by soredia and isidia. Sexual reproduction involves fungal partner of the lichen thallus. Most lichens resemble the fungi belonging to ascomycetes or basidiomycetes as they produce either ascospores or basidiospores.

Asexual reproduction;

Asexual reproduction takes place by following methods:

1. Fragmentation:On maturity, the older portions of the thalli of lichens die and decay. The thallus breaks into pieces accidentally and each piece develops into a new plant. This occurs more frequently in pendant thallus, such as of Ramalina reticulate.
   
   
2. By soredia:Soredia are spherical bundles of fungal filaments and algal cells that are produced in the algal region (usually the medulla) and rupture through the thallus to the outside. They give the thallus a powdery appearance. The soredia blow away and germinate to produce a new lichen. Aggregates of soredia on the lichen surface are called Somalia. Soredia may be laminal or marginal.
   
   
3. Isidia: Isidia are tiny peg-like or finger-like structures containing fungal filaments and some photobiont cells. They are found on the surface of lichens and are nearly always laminal. Isidia break off and colonize new areas in a similar manner to soredia.

Sexual reproduction;

Sexual reproduction involves fungal partner of the lichen thallus. Most lichens resemble the fungi belonging to ascomycetes or basidiomycetes as they produce either ascospores or basidiospores.

Male reproductive organ ( Spermogonium );

The flask-shaped structure also called spermogonia or picnic. Found embedded in the thallus, opens outside by small pore called ostioles. The hype lining the inner surface of the spermogonium produce numerous non-motile gametes called spermatia which are set free in a slimy mass which oozes out through the ostioles.

Female reproductive organ ( Carpogonium );

Multicellular that develops in the medulla of the young lobes of the thallus. Consists two portions that are coiled portions having multicellular ascogonium and the upper straight portion also called trichogyne which is also multicellular.