Lichens form fine cracks in desert and mountain rocks. Carbon dioxide produced by lichen respiration combines with rainwater to form carbonic acid. Carbonic acid disintegrates stone. Lichen corpses mix with crushed rock to form humus. Soil is formed through the formation of humus.

The use of lichen in drug production is-
(i) Erythrin is produced from the lichen Rocella montagnei. Erythrin is used to treat angina or heart disease.
(ii) Usno and Evosin creams (antiseptics) derived from lichens are used to prevent tumors and viruses and to treat pain.
(iii) Lichenin and Isolichenin from lichens inhibit tumors.
(iv) Peltigera canina is used in rabies and Cladonia cristatella as medicine for whooping cough. Dr. Siddique Publications
(v) Medicines for jaundice, diarrhoea, fever and skin diseases are prepared from lichens.
(vi) Cetraria islandica is used as a medicine for tuberculosis.
(vii) Usonic acid produced from lichens acts as an antibiotic against gram positive bacteria.
(viii) Proteoleicesteric acid produced from lichens is used as an anti-cancer agent.
(ix) Lobaria pulmonaria lichen is used to treat lung diseases.
(x) Xanthoria is used to treat jaundice.

Lichen bolga called reindeer moss (Cladonia rangiferina) is a favorite food of deer and cattle in the tundra region. Lichens such as Labaria pulmonaria, Ramalina fraxinea, Evernea prunastri, Cetraria islandica etc. are used as cattle fodder. Caribou, chamois and other wildlife depend heavily on lichen.

Lichens are used as human food due to the sugar called ‘lichenin’. Cetraria islandica in Norway, Sweden and Iceland, Evernia prunastri in Egypt, Parmelia sulcata in India and Endocarpon miniatum (stone mushroom) in China and Japan are used as human food.

1. Human food: Lichens are used as human food due to the sugar called ‘lichenin’. Cetraria islandica in Norway, Sweden and Iceland, Evernia prunastri in Egypt, Parmelia sulcata in India and Endocarpon miniatum (stone mushroom) in China and Japan are used as human food.
2. Animal food: Lichen bolga called reindeer moss (Cladonia rangiferina) is a favorite food of deer and cattle in the tundra region. Lichens such as Labaria pulmonaria, Ramalina fraxinea, Evernea prunastri, Cetraria islandica etc. are used as cattle fodder. Caribou, chamois and other wildlife depend heavily on lichen.
3. Drug production: The use of lichen in drug production is-
(i) Erythrin is produced from the lichen Rocella montagnei. Erythrin is used to treat angina or heart disease.
(ii) Usno and Evosin creams (antiseptics) derived from lichens are used to prevent tumors and viruses and to treat pain.
(iii) Lichenin and Isolichenin from lichens inhibit tumors.
(iv) Peltigera canina is used in rabies and Cladonia cristatella as medicine for whooping cough. Dr. Siddique Publications
(v) Medicines for jaundice, diarrhoea, fever and skin diseases are prepared from lichens.
(vi) Cetraria islandica is used as a medicine for tuberculosis.
(vii) Usonic acid produced from lichens acts as an antibiotic against gram positive bacteria.
(viii) Proteoleicesteric acid produced from lichens is used as an anti-cancer agent.
(ix) Lobaria pulmonaria lichen is used to treat lung diseases.
(x) Xanthoria is used to treat jaundice.
4. Treatment of plant diseases: sodium usinate from lichens is used in tomato canker disease and licanoric acid in tobacco mosaic disease.
5. Soil Formation: Lichens form fine cracks in desert and mountain rocks. Carbon dioxide produced by lichen respiration combines with rainwater to form carbonic acid. Carbonic acid disintegrates stone. Lichen corpses mix with crushed rock to form humus. Soil is formed through the formation of humus.
6. Insect food: Caloplaca saxicola, Circinaria calcaea, Begonia lichenora, Aspicilia cinerea etc. are used as food for ants, caterpillars and snails.
7. Dye making: Valuable blues called archil and cadbear are made from lichens. Archil and orsine prepared from Rocella tinctoria are used to stain microscopic objects. Red and purple dyes are made from Ochrolechia androgyna and Ochrolechia tartaria. It is used to dye woolen and silk fabrics.
8. Preparation of litmus paper: Litmus paper is prepared from lichens called Rocella montaignei and Lasallia papulosa.
9. Tannin production: Tannins are obtained from Cetraria islandica and Lobaria pulmonaria which are used in leather tanning.
10. Chemical constituents: Lichen contains more than 550 natural constituents. Lichens, zeorin, calycin, phycion, xanthomus, terpenoids, benzyl starch, usonic acid, rhizocarpic acid, salagenic acid (Ramalina fraxinea), lecanric acid (Parmelia saxatilis), squamatic acid (Cladonia rangiferina), arsenic acid, zeorin etc. goes
11. Preparation of stimulants: Alcohol, beer etc. are prepared from Usnea filipendula and Ramalia dumeticola.
12. Perfumery: Evernia prunastri and Pseudevernia furfuracea yield naphthalene, camphor, geraniol and bornel. Soaps, perfumes and other cosmetics are made with these ingredients.
13. Pollution Indicators: Lichens act as environmental pollution indicators. If lichen grows in a polluted area, it can be understood that air pollution is decreasing in that area.
14. In Industry: Lichen is used for tanning leather in leather industry.
15. Frost progression: Lichens are the first plants to grow in deserts and initiate the Xeroseries.

The reproductive organs of lichens are ascocarps or basidiocarps. Sexual reproduction of lichens also occurs through plasmogamy. Male genitalia of lichens are called spermagonia and female genitalia are called carpogonia. Spermagonium produces pungametes and carpogonium produces strigametes. The male gamete and female gamete unite to form the zygote. The zygote germinates to form a new lichen.

Leaf-like phyllidia are produced in foliose lichens. Lichens reproduce by phyllidia.

Pycnidiospores are produced inside the pycnidium. Pycnidiospores germinate to form new lichens.

Isidium is a tiny papilla like spore. It grows and metamorphoses to form new lichens.

Soredium is a tiny body of algae covered with fungi. It is dispersed by wind and germinates in favorable conditions to form new lichens.