Lichenology

includes general characters, reproduction and economic importance of lichen

1. LICHENOLOGY SUBMITTED BY DIVYA VARGHESE I MSC BOTANY S119/18 SUBMITTED TO NITHU MISS DEPT.OF BOTANY

2. CONTENTS 1. GENERAL CHARACTERS 2. REPRODUCTION 3. ECONOMIC IMPORTANCE

3. LICHENS They are small group of plants Almost 16000 species were found Lichens is a combination of two different members be­longing to two different groups, i.e., one is a fungal com­ponent while the another is an algal component. So, it is a dual organism. Algal component is called phycobiont while the fungal component is known as mycobiont .

4. LICHENOLOGY:- The branch of science which deals with study of lichens is called lichenology A scientist who has specilized in the study of lichen is called Lichenologist SYMBOISIS:- symbiosis is used to describe the intimate association between two distantly, related species that are mutually benefiting from this association. These associations are obligatory ones in which neither organisms can survive in nature if the two organisms are separated.

5. In lichen symboitic association can be seen between algae and fungi Algae synthesize necessary carbhohydrates with help of its green chloroplasts. Thus algae provide food for fungi Fungi absorb water and minerals from the substratum and provide food for fungi Lichens mainly grow on roof of house, tree bark, rocky surfaces etc….. They are xerophytic in nature can withstand long period of time in drought condition

6. Lichens are most widely distributed group of plants The factors help for wide distribution :-  their symboitic life  their prolific methods of vegetative propagation and efficient spore dispersal  resistance to temprature and moisture which enable them to grow to all places

7. Systematic position DIVISION : Mycota SUB-DIVISION : Eumycota CLASS : Lichens SUB CLASS : Ascolichens SERIES : Gymnocarpae ORDER : Parmeliales FAMILY : Usneaceae GENUS : Usnea

8. Thallus structure Plant body of lichen is called thallus They may seen as leaf like form, powdery form or in an intermediate form Classification of lichen according to thallus structure Crustose lichen Foliose lichen Fruticose lichen

9. 1.Crustose lichen These are very closely adhered to the substratum on which they are present, and give a crust-like appearance. It is very difficult to separate them from their substratum. Fruiting bodies are present on the upper surface e.g., Graphis scripta , Lacidia , Verrucaria , etc.

10. Crustose lichen

11. 2.Foliose lichen Thallus in these lichens is flat, leaf-like, well-branched and attached to the sub­stratum with the help of rhizines e.g., Physcia , Parmelia, Peltidea , etc.

12. 3.Fruticose lichen Lichens of this category are well-branched structures which are generally erect or sometimes prostrate, and give shrub like appearance e.g., Usnea, Cladonia, Everinea , etc.

13. Internal Structure of Lichens

14. Internally, a foliose lichen is divisible into four dif­ferent regions, i.e., upper cortex, algal zone, medulla and lower cortex Upper cortex :-is a thick, protective layer made up of dense, closely woven pseudoparenchymatous mass of fungal hyphae. Outer to this, an epidernal layer may or may not be present. Algal zone :- consists of mostly blue-green, or green algal filaments of Cyanophyceae or Chlorophyceae . Some fungal hyphae also remain embedded in this layer. Com­mon algal members are Nostoc , Gloeocapsa , Rivularia and Chlorella. This is also known as gonidial layer.

15. Medulla: forms the central region of the lichen. It consists of loose mass of fungal hyphae. Lower cortex:- forms the lower surface of lichen and from this arises rhizines . It is composed of densely packed hyphae.

16. Peculiar vegetative structures in lichen Breathing pores Cyphallae Isidia Cephallodia soredia

17. 1.Breathing pores In the upper cortex of some foliose and fruticose lichens, the hyphae are very loosely interwoven to facilitate the gaseous exchange between thallus and atmosphere These localized areas may be depressions or cone like and are known as breathing pores

18. 2.Cyphellae They are aerating organs Seen in lower cortex of foliose lichens as circular cavities Example:- Sticta sylvatica

19. 3. Isidia They are small , stalked coral like outgrowths from the upper surface of lichen thallus Function is increase the photosynthetic surface of thallus

20. 4. cephallodia They are externally or internally gall like outgrowths, generally of dark color on the lichen thalli They consists of same fungal hyphae as in the thallus but the algal component is different

21. 5.Soredia They are small bud like outgrowths on lichen thalli Greyish in color Soredia sometime produce a pustule like outgrowth is called sorelium

22. REPRODUCTION 1. VEGETATIVE REP0RODUCTION 2. ASEXUAL REPRODUCTION 3. SEXUAL REPRODUCTION

23. VEGETATIVE REPRODUCTION Take place by 3 methods Fragmentation Soredia isidia

24. 1.By Fragmentation. Death and decay of older parts of the thallus produce smaller pieces which give rise to new thallus. Sometimes the broken pieces (fragments) develop into new thalli , provided they contain both the algal and fungal components.

25. 2. By Soredia . It is the most common method of vegetative reproduction. These are small protuberances, produced on the upper surface by the thallus. They may either occur within definite pustule-like compact structures called soralium or may arise so abundantly as to spread up like a thin greyish layer of dust. Each soredium consists of a few algae cells surrounded by a mass of hyphae.

26. Soredia are very light in weight and are easily disseminated by wind or rain wash. After falling on suitable substratum, they develop into a new lichen e.g., Parmelia, Bryoria etc.

27. 2.By Isidia: These are the stalked, un-detachable outgrowths produced by the thallus on its upper surface . Like soredia , the isidia are also composed of both fungal and alga, components but differ from them in being covered with a definite cortex. The algal component is of the same kind as in thallus. The isidia may be rod shaped (Parmelia sexualities), coralloid ( Umblicaria postulata ), cigar shaped (Usnea comosa ) scale shaped ( collema crispum ).

28. The main function of the isidia is to increase the photosynthetic surface of the thallus. Sometimes these also act as organs of vegetative propagation .

29. ASEXUAL REPRODUCTION By Sporulation: Certain lichens may also reproduce asexually by means of conidia (e.g., Arthonia), oidia and Pycniospores or pycnidiospores In some cases hyphae break down into small pieces known as oidia

30. Pycniospores :-are produced within the flask shaped structures known as pycnidia Each pycnidium opens to the surface through a small pore known as ostiole. The pycnidial wall is made up of sterile fungal hyphae. Inside the pycnidia fertile hyphae contain sexual spores (pycnidiospores) at their tips.

31. After falling on suitable substratum pycnidiospores germinate and coming in contact with appropriate alga, they develop further into a new lichen.

32. SEXUAL REPRODUCTION The sexual reproduction in Ascolichens and Basidiolichens is like class Ascomycetes and Basidiomycetes respectively. Ascolichens have been studied in more detail from this point of view. The male reproductive organ is called the spermogonium and the female is known as carpogonium. They develop either on the same hypha or on two different hyphae of the same mycelium.

33. Spermogonium: The spermogonia are flask shaped structures embedded in the upper surface of the thallus. They open outside by a small pore known as ostiole. The fertile hyphae in the cavity of the spermogonium abstract minute rounded cells at its tip. These male cells are known as spermatia. In some species of lichens, however, the pycnidia like structures also function as spermogonia They are non-motile

34. Carpogonium: A carpogonium consists of two parts -lower coiled multicellular portion called ascogonium -upper long, Straight, thread like portion called trichogyne. The ascogonium lies deep in the medullary portion while trichogyne emerges out of the thallus and receives spermatia.

35. Fertilization Spermatia have been found adhering to the gelatinous wall of trichogyne The point of contact between trichogyne and spermatia dissolves The contents of spermatium migrate to the trichogyne through the pores Some scientists rejected this view points

36. The other view is:- Gradual withering of trichogyne Development of fully branched ascogenous hyphae from the ascogonium Formation of asci at the ends of ascogenous hyphae Development of an envelope of sterile hyphae around the developing asci, the ascogenous hyphae and ascogonium to form a frutification called apothecium

37. Structure of Apothecium It is cup shaped structure Reddish or brown in color If the apothecium consists only the fungal component, it is known as lecideine type (e.g., Lecidea, Cladonia, Gyrophora ) If it consists bath algal and fungal components it is known as lecanorine type (e.g., Lecanora, Parmelia).

38. 1) Disc of the Apothecium: Hymenium (Thecium ): It is the upper-most fertile layer of apothecium consisting of a closely packed, palisade like layer of sac-like asci and sterile hair like fungal hyphae known as paraphyses . This layer is also called hymenial layer or hymenium . Each ascus contains 8 ascospores Ascospores are of various shapes and size, multicellular uni- or bitunicate and uni- or multinucleate

39. (b) Sub-hymenium: The region consists of the closely interwoven sterile hyphae . It is present just below the fertile layer. (2) Margin of Apothecium: This part surrounds the disc and also forms the edge of the apothecium.

40. Germination of ascospores : The ascospores may be simple or septate . They are very light in weight and easily disseminated to a long distance by wind . After falling on suitable substratum it germinates and produces fungal hyphae. The hypha grows into a new lichen thallus , if it comes in contact with an appropriate algal component .

41. PERITHECIA Flask shaped structure Seen embedded in upper thallus Cavity lined by asci Intermingled by paraphyses Open to outside by means of ostiole Smaller than apothecia

42. Economic Importance of Lichens (1) 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).

43. (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 ..

44. (b) Food and Fodder: The lichens serve as 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 man during famines . They are rich in polysaccharides, certain enzymes and some vitamins.

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

46. (d) In Industry: ( i ) Tanning and dyeing: Some lichens are used in leather industry . Cetraria islandica and Lobaria pulmortaria show the astringent property. This astringent substance is extracted from the thallus and is used in tannin 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.

47. (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 (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 confectionary.

48. 2. Harmful Effects: a) Lichens growing on young fruit trees and sandal trees are harmful to the plant. (b) During 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

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