The lichen from which litmus is obtained is

Riccia tinctoria

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 two edible lichens are:

1)Parmelia perlata

2) Lecanora esculenta

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 fungus taking part in the formation of lichen is called mycobiont and the algal component of lichen is called phycobiont.

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.

The physiological resemblances between algae and fungi are as follows:

1) Vascular tissues are absent in both of them.

2) They reproduce by spores during favourable conditions.

3) Sex organs are unicellular, simple and non jacketed.

4) Embryo is not formed after fertilization.

5) Asexual reproduction by mitospores is quite common.