This document provides information about lichens. It begins with a definition of lichenology as the study of lichens. It then discusses the symbiotic relationship between algae and fungi that makes up a lichen. Various structures of lichen thalli are described, including crustose, foliose, and fruticose forms. The document outlines lichen reproduction through vegetative means like soredia and isidia, and sexually through structures like spermogonia, carpogonia, and apothecia. It concludes by noting lichens are widely distributed due to their symbiosis and efficient dispersal methods.

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

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.

5. oLICHENOLOGY:- The branch of science which deals with
study of lichens is called lichenology
oA scientist who has specilized in the study of lichen is
called Lichenologist
oSYMBOISIS:- 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.

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

7. 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

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

9. 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
1. Crustose lichen
2. Foliose lichen
3. Fruticose lichen

10. 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.

11. Crustose lichen

12. 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.

13. 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.

15. Internal Structure of Lichens

16. 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.

17. 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.

18. Peculiar vegetative structures in
lichen
1. Breathing pores
2. Cyphallae
3. Isidia
4. Cephallodia
5. soredia

19. 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

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

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

22. 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

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

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

25. VEGETATIVE REPRODUCTION
• Take place by 3 methods
1. Fragmentation
2. Soredia
3. isidia

26. 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.

27. 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.

28.  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.

29. 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).

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

31. 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

32. 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.


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

34. 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.

35. 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

36. 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.

38. 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

39. 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

40. 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).

41. 1) Disc of the Apothecium:
(a)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.
o This layer is also called hymenial layer or hymenium.
o Each ascus contains 8 ascospores
o Ascospores are of various shapes and size,
multicellular uni- or bitunicate and uni- or
multinucleate

42. (b) Sub-hymenium:
oThe region consists of the closely interwoven sterile
hyphae.
o 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.

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

45. 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

46. 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).

47. (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..

48. (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.

49. (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

50. (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.

51. (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.

52. 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