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4.Leprose lichen:, Single or small cluster of algal cells are enveloped by fungal hyphae, forming simple thallus providing a powdery appearance., No distinct fungal layer., Example:- Leprasia incana., , 5.Filamentous Lichen:, The algal partner is filamentous, well developed and remains ensheathed, or covered by only a few hyphae., Example:- Coenogonium, Racodium, Cystocoleus., , Figure1. Types of Lichen Thalli, Intrenal Structure, The internal structure of Lichen is very complex., The thallus is composed of fungal and photobiont cells, so well united as to give the, impression that you are looking at just one organism.
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On the basis of internal structure mainly, the distribution of algal component, among fungal component two types of foliose lichen are recognized., , 1. Homoiomerous type:The algae are more or less uniformly distributed., The algae are gelatinous and belong to Myxophyceae., The fungi form the inter protective layer of the thallus., Example:- Collema, Leptogium, , Figure2. Homoiomerous Type, 2. Heteromerous type:The thallus in cross-section shows upper cortex, algal layer, medulla and lower, cortex., , Upper Cortex=>, Outer most thick and protective zone of the thallus composed of compactly, interwoven fungal hyphae., Hyphae are arranged at right angle to the surface of the thallus., Have no inter cellular spaces between hyphae. If space present then filled with, gelatinous substance..Breathing pores are present in Parmelia for gaseous exchange., , Algal Layer=>, Found below upper cortex.
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Also called as gonidial layer., Algal cells are embedded in between tangled network of loosely interwoven hyphae., , Medulla=>, Central part of the thallus., Loosely interwoven fungal hyphae with large space between them., , Lower Cortex=> Composed of compactly arranged hyphae which run parallel or, perpendicular to the surface of the thallus., Some hyphae extended downward from lower cortex and form root-like bundles, called rhizines, which help in anchoring the thallus to the substrate., Structure of crustose and fructicose lichen is also similar but in fructicose only lower, cortex absent due to their cylindrical structure., , Figure3. Heteromerous Type, Reprodcution in Lichen, Lichen reproduces by vegetative, asexual and sexual means., A. Vegetative reproduction, 1. Fragmentation:, On maturity the older portions of the thalli of lichens die and decay., The thallus breaks into pieces accidentally and each piece develops into a new plant., Ramalina reticulata.
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Figure8. Lichen: Female sex organ, Male sex organ is called Spergonia (flask shaped). It forms male gamete called, Sermatia. It develop close to carpogonia . This enables spermatia to adhere to the, projected part of sticky trichogyne on dissolution of walls, nucleus of spermatia, migrates to female nucleus and fuse with it., , Figure9. Lichen: Male sex organ
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Economic Importance of Lichen, Lichens are wonderful gift of nature. They are the source of food, medicines, flavours and, stains., , Useful activities of lichen, 1. As food and fodder, Lichens are important constituents of food in North Polar Tundra and Eastern Siberian, region., Species of Lecanora, Parmelia (as curry powder in India), Umbillicaria (used in, Japan) and Cetraria are used as food., Evernia prunastri are used for making breads in Egypt., In France lichen are used for making chocolates, pastries. Endocarpon miniatum used, as vegetables., Aspicilia calcarea, Lecanora saxicola are used as food by mites, snails, caterpillars, and termites., Lobaria pulmonaria, Evernia prunastri, Ramalina fraxinea and Ramalina fastigiata, are used as fodder for animals because of great nutritive value due to presence of, Lichenin., Cladonia rangifera serves as food for reindeer and musk ox., Dries lichens are fed to horses and swans., 2. As medicine, Medicinal value of lichen is due to the presence of Lichenin and some, astringent substances., Some lichens are used in the treatment of bile, diarrhoea, fever, nervous, disorders, and hydrophobia and skin diseases., Parmelia is used in snake and scorpion bites., Cladonia, Cetraria and Pertusaria in intermittent fever., Cladonia pyxidata in whooping cough., Species of Usnea stop bleeding., Usnic acid obtain from Usnea and Cladonia used in infections., Cetraria islandica used in tuberculosis and other lung diseases., 3. As dyes, Red and purple dye obtain from Ochrolechia androgyna, Ochrolechia tartaria, Orchil a blue dye obtain from cetraria icelendica ., Brown dye obtained from Parmelia omphalodes., Litmus an important acid base indicator dye in chemical laboratories obtains, from Roccella montagnei and Lasallia pustulata., 4. In tannin industry, Cetraria icelandica, Lobaria pulmonaria used as tannin agent in leather, industries.
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5. In cosmetic and perfumery, Evernia and Ramalina are source of essential oils used in manufacturing of, cosmetic soaps., Lichens are used in hawan samagries, dhup, perfumeries because of pleasant, smell., 6.In fermentation and distillation process, In Russia, Sweden and Siberia liquors are manufactured by fermentation and, distillation of lichen like Cladonia rangiferina and Ramalina fraxinea., 7. As culture media, Lichens are important constituents of some culture media for the culture of, fungi and bacteria in laboratories., 8. Ecological importance, Lichens are pioneer plants which help in colonisation of bare rocky habitat., Lichens serve as indicators of air pollution., , 9. As nitrogen fixers, Lichens with with blue green algal phycobionts play an important role in provining, fixed nitrogen in certain ecosystem., , Harmful activities of Lichen, Lichens cause loss of the surface of glasses and marble stones., Long threads of pendant lichens like Usnea are inflammable, thus help in spreading, forest fire., Lichen like Cladonia cause total destruction to the colonies of mosses by direct, parasitic attack, , Books Cited : 1., 2., 3., 4., , Saxena, R.S. 2018. Text Book B.Sc. Botany-1., Singh, A. P. and Pushkar, Kumar. Life Sciences., Singh, R. K. 2018. Fundamentals of Botany., Singh, V., Pande , S.N. and Jain 2010. Text Book of Botany.
