describe crustose, foliose and fruticose in brief 

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...

Where do lichens grow?

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.

write any six characteristics of lichens 

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.