Lichens are called bio indicators as they indicate the environmental pollution through their gradual extinction in those regions where there is excessive pollution especially the air pollution.

Lichens reproduce asexually by:

1) Fragmentation

2)By soredia (small rounded bud like outgrowths developed in the form of greyish white or green powder on the upper surface of thallus.

3)By isidia (small papillate outgrowths developed on the thallus)

The two edible lichens are:

1)Parmelia perlata

2) Lecanora esculenta

Lichens grow on the old walls, trunk of trees , bare ground and the rocks .Some lichens (crustose lichens) secrete acids into rocks and disintegrate them to soil particles from which vegetation arises so they are also called pioneers of vegetation.

The lichen from which litmus is obtained is

Riccia tinctoria

Lichens are the "dual or composite"organisms formed by the symbiotic associationbetween "algae and fungi".

They are the simple slow-growing plant that typically forms a low crusty, leaf-like or branching growth on rocks, walls and trees.

Example:

Peltigera Canina,Cristatella, Cretariaislandica,Parmelia(genus)

Theophrastus (371-284BC) coined the term Lichen.

Lichenology is the branch of mycology that studies the lichens, symbiotic organism made up of a intimate symbiotic association of a microscopic algae with a filamentous fungus.

Erik Acharius is the father of lichenology.

the six characteristics of lichen are :

1.Lichen secrete lichenic acid that help in disintegration of rocks.

2.the plant body of the lichen is called thallus.

3.lichen show asexual, sexual and vegetative method of reproduction.

4.Vegetative reproduction take place by fragmentation ,decaying of older parts, lobules .

5.Asexual reproduction take place by formation of oidia .

6.Sexual reproduction take place by formation of male sex organ and female sex organ.

Lichen are the dual organism formed by symbiotic association between algae and fungi .

they are generally visible on the surface. On the basis of their nature of thallus they are classified into crustose ,foliose and fructose .

a)crustose lichen (crust like):it is the lichen that forms thin crust over the substratum. They are found growing on surface of rocks, on the wall and bank of tree. Example are Graphis and Lecidea etc.

b)Foliose Lichen: it is the lichen that have a flat and leaf like...