· Term lichen was given by Theophrastus.
· Composite dual organisms.
· Symbiotic association between algae and fungi.

· Pioneer colonizers of barren rocks and mountains.
· The fungal partner absorb water and minerals from the substratum and algae prepare necessary food for both in
· The algal component lichen usually belongs to Cyanophyceae (Nostoc, Scytonema). While fungal members usually belong to Ascomycetes and Basidiomycetes.

· Many of the species of lichens can grow under extreme conditions of humidity and temperature.

A. Habitat
· Corticolous – growing on the bark of the tree.
· Saxicolous – growing on rocky substrata or stone.
· Terricolous – growing on the ground
· Lignicolos – developing on wood eg. cyphelium
· Marine – developing inshore of the sea.

B. Types
· Based on the general habit of growth form and manner of attachment to the substratum they are divided into

A. Crustose lichen
– Forms a thin crust closely adhered to the substratum, partly or wholly embedded into it.
E.g. Graphis, Rhizocarposs, Dermatocarpon

B. Foliose lichen – flat, leaf-like, well-branched, or lobed thalli attached to the substratum at few points by means of rhizines. 
E.g. Peltigera, parmelia.

C. Fruticose lichens
– they form much-branched shrub-like bodies and remain attached to the substrate by their narrow basal portion only. 
Eg. Reindeer moss (Cladonia), old man's beard (Usnea).

C. Reproduction
· Reproduces by both Sexual (only by mycobiont fungal partner) Asexual method and the vegetative method.
· Asexual reproduction is by fragmentation.

1. Vegetative reproduction
This may take place by any of the following structures:

(a) Soridia: They are tiny granular bodies occurring in large numbers on the upper surface.
· Each soredium consists of one to may algal cells wrapped by fungal hyphae as in usnea and Cladonia.
· Soridia is the commonest method of reproduction in lichen
· These soredia are blown about by the wind and they germinate directly into lichen thalli.

(b) Isidia: These are small outgrowth on the surface of lichen thallus, which separates from the parent thallus and develops into a new thallus.
· Each isidium consists of both algal and fungal hyphae as usual but is surrounded by a layer of the cortex.
· Isidia are primarily photosynthetic in function but sometimes they get detached from the parent thallus then they develop into new thalli.

(c) Cephalodia: They appear dark-coloured swelling on the upper surface of the thallus, sometimes internally also.

2. Sexual reproduction:
· Sexual reproduction takes place in certain Asco-lichens, the fungus alone takes part in this process.
· Sexual reproduction results in the formation of a fruiting body, commonly a cup-shaped Apothecium. In some cases, a flask-shaped called perithecium.

D. VVI Uses of Lichens
· Pioneer colonizers of rocky habitat and responsible for primary succession.
· Bioindicators of air pollution (extremely sensitive to SO2)
· Rocella tinctoria is the source of litmus.
· Usnic acid obtained from usnea (old man's beard) is an antibiotic
· Cladonia (Reinder moss)- Food for Reinder, medicine for whooping cough
· Parmelia source of medicine for Epilepsy.
· Many lichens such as Cetraria islandica (Iceland moss), Dermatocarpon (stone mushroom) are used as food.
· Lichens are often used in perfume industries.

E. Economic Importance of Lichen
A. Useful Aspects:

(a) Ecological significance:

(i) Pioneer colonizers: Lichens are said to be the pioneers in establishing vegetation on bare rocky areas (lithosere). They are the first members to colonize the barren rocky area. During development, they bring about the disintegration of rock stones (biological weathering) by forming acids e.g., oxalic acid, carbonic acid, etc. Thus, they play an important role in nature in the formation of soil (a phenomenon called pedogenesis).

(ii) Role in environmental pollution: Lichens are very sensitive to atmospheric pollutants such as sulphur dioxide. They are unable to grow in towns, cities, and around industrial sites such as oil refineries and brickworks. So, the lichens can be used as reliable biological indicators of pollution. By studying lichens on trees, a qualitative scale has been devised for the estimation of the mean SO2 level in a given season. Thus lichens are used as pollution monitors.

(b) Food and Fodder: The lichens serve as an important source of food for invertebrates. A large number of animals, for example, mites, caterpillars, termites, snails, slugs, etc. feed partly or completely on lichens. Lichens as food have also been used by men during famines. They are rich in polysaccharides, certain enzymes, and some vitamins.
Cetraria islandica (Iceland moss) is taken as food in Sweden, Norway, Scandinavian countries, Iceland, etc. Lecanora esculenta is used as food in Israel and Umbilicaria esculenta in Japan. Species of Parmelia (known as rathapu or ‘rock flower’ in Telgu) are used as curry powder in India.
In France, lichens are used in confectionery for making chocolates and pastries.
Cladonia rangiferina (Reindeer moss) is the main food for reindeers (a kind of deer) in polar countries. Cetraria islandica is also used as fodder for horses.
Species of Stereocaulon, Evernia, Parmelia, and Lecanora are also used as fodder.

(c) Source of Medicines: Since very early times the lichens are used to cure jaundice, fever, diarrhoea, epilepsy, hydrophobia, and various skin diseases. Various lichens are of great medicinal.

(i) Lobaria pulmonaria and Cetraria islandica In respiratory diseases particularly tuberculosis
(ii) Usnea barbata For strengthening hair and for uterine ailments
(iii) Xanthoria parietina For jaundice
(iv) Cladonia spp. For whooping cough
(v) Peltigera canina (dog lichen) For hydrophobia
(vi) Roccella montagnei In angina, a serious heart disease
(vii) Parmelia saxatilis For epilepsy
(viii) Species of Evernia, Cladonia and Poccella To control fever

A yellow substance usnic acid is obtained from species of Usnea and Cladonia. It is a broad-spectrum antibiotic and is used in the treatment of various infections. It is effective against gram-positive bacteria. Some lichen compounds e.g., lichenin, iso-lichenin have anti-tumour properties.

Protolichesterinic acid, a compound obtained from some lichens, is used in the preparation of anti-cancer drugs. Erythrin obtained from Roccella montagnei, is used to cure angina. Many antiseptic creams such as Usno and Evosin are available in the market and are well known for their antitumor, spasmolytic and antiviral activities.

(d) In Industry:
(i) Tanning and dyeing:

Some lichens are used in the leather industry. Cetraria islandica and Lobaria pulmonaria show the astringent property.
This astringent substance is extracted from the thallus and is used in the tanning industry. Lichens are also used in preparing natural dyes. Orchil, a blue dye obtained from Roccella and Leconara, is used to dye woollen articles and silk fabrics.
It is purified as orcum and used as a biological stain. A brown dye is obtained from Parmelia spp. whereas Ochrolechia spp. yield a red dye.

Litmus used as an acid-base indicator is also a dye and is obtained from Roccella tinctoria and Lasallia pustulata.

(ii) Cosmetics and perfumes:

Evernia, Ramalina, Pseudorina are reported to have perfumed volatile oils. Due to the aromatic substances present in the thallus, the lichens are used in the preparation of various cosmetic articles, perfumery goods, dhoop, hawan samagris, etc.

(iii) Brewing and distillation:

Some species of lichen, for example, Cetraria islandica contain carbohydrates in the form of lichenin. In Sweden and Russia, alcohol is produced from these lichens. These lichens are also used in confectionery.

(iv) Minerals:
Lecanora esculenta is found in limestone deserts and yields a large amount of calcium oxalate crystals. These are 60% of its dry weight.

(e) Natural products:
Lichens are known to produce over 550 natural products. Some important natural products are:

Product Produced From
Salazinic acid Ramalina siliquosa
Squamatic Acid Cladonia crispate
Lecanoric acid Parmelia Subrudecta

(f) Poison from Lichens:
Some lichens are poisonous due to presence of various substances in them:

Poisonous due to
Letharia vulphina (wolf moss) Vulpinic acid (used as a poison for Wolves)
Cetraria juniperina Pinastrinic acid
Parmelia molliuscula Selenium
Xanthor ia parietina Beryllium
Everina furfuracea Chlorine

B. Harmful Aspects:
(a) Lichens growing on young fruit trees and sandal trees are harmful to the plant.
(b) During the hot season some species of lichens (e.g., Usnea barbarata) become so dry and inflammable that they often help in spreading forest fire.
(c) Some lichens act as allergens.
d) The commercial value of glass and marble stone is reduced because of itching of their surface by lichens.
(e) Some lichens e.g., Cladonia rangifera, Cetraria islandica accumulate large quantities of radioactive strontium (Sr90 ) and caesium (Cs137 ) from atomic fall-outs.
These may be incorporated in the food chain, lichen → reindeer → man, leading to their accumulation in human tissues

High Yielding Points of Lichen

1. In lichen fungi perform the function of reproduction, absorption, and protection (@rap) but only prepares the food so algae can live without fungi but the reverse is not possible.

2. Lichen which can fix the nitrogen are called AZOTODESMIC LICHEN.

3 In lichen, the male reproductive organ is spermogonium and the female reproductive organ is carpogonium (which has upper part trichogyne and lower coiled part ascogonium)

4. In lichen asexual reproduction occurs bypycnidiospores and pycnispores.

5. In lichen the structure cephaloid helps to retain the moisture.

Lichens are good absorbers of radioactivity.

7. The chlorophyll of the algal partner of the fungi absorbs the SO2 to replace the Mg++ which results in the formation of toxin pheophytin which causes the death of lichen.

8. The relation in a lichen is of master and slave c/a HELOTISM (given by Crombie)

9. The lichen Evernia Prunastriis was used for making the perfume.

10. Lichens such as Cetraria Junierpernia and Letharia vulpine are used for poisoning.

11. In lichen vegetative reproduction occurred by isidia (these are the outgrowth of the lichen thallus which after detachment can form the new thallus)

12. Classes of lichens:

A. Crustose Lichen: The algal and fungal partners are uniformly distributed and cannot be detached by destroying the whole thallus.
Eg: Rhizocarpon, Graphics, Lechonera, and Dermatocarpen (@ Rhiza Gi GRAPHICS LEca DE na.

B. Foliose lichen:
These have flat, leaf-like, well-developed lobed thalli attached to the substrate by means of rhizine.
Eg: Parmelia, Peltigera, Physcia (3p).

C. Fructose lichen: These are much-branched lichens with a bushy appearance.
Eg: Cladonia, Cetraria, usnea (2CU)

Also, Read Notes of Other Lessons of Botany:

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