This document provides an overview of lichens. It begins with definitions, describing lichens as a symbiotic association between fungi and algae or cyanobacteria. It then covers the history of lichen research, habitats of lichens, ways of classifying lichens, their structure and reproduction methods. The document discusses lichens' economic importance, including as a food source, in medicine, dye production, and their use as bioindicators of environmental pollution. It concludes with an explanation of lichenometry, which uses lichen growth rates to determine the age of exposed rocks.

1. Submitted by:-
Priyanka Dixit
M.Sc previous
Submitted to:-
Prof. Samuel G Singh Sir

2. CONTENT
 Introduction
 Definitions
 History
 Habitat
 Classification
 Nature of association
 Composition
 Structure
 Reproduction
 Economic importance
 Lichen as bioindicator
 Lichenometry

3. Introduction
Lichens are considered plant-like organisms that show
symbiotic association with algae , till now there are
15,000 species of lichen. They mainly show symbiotic
association with green algae or cyanobacteria and
fungi (mostly ascomycetes and basidiomycetes) .They
are found all across the world depending on the
condition of the environment . They are majorly found
in colony form , like on the tree bark , exposed rock ,
and as a part of biological soil crust .
Lichens are also used as human beings as a source of
food along with medicine extraction and dye . They are
also considered a major source of food for reindeer a
major source of food for reindeer that roam the far
northern ranges .

4. Definitions
• Lichen: structurally organized permanent symbiotic
association of fungi and algae .
• Lichenology: Branch of biology deals with study of lichen.
• Mycobiont: Fungal component of lichen.
• Phycobiont: Algal component of lichen.
• Symbiosis: Association/interaction of organisms where
both partners are mutually benefitted.
• Algae in turn supplies organic food to fungus.
• Fungus protect algae from unfavorable conditions.
• This type of symbiosis is called as heliotism (master and
slave relationship)
• Fungal component is prominent in lichen than algal
component.
• Growth of lichen is very slow.
• Lichen produce a specific acid known as lichen acid.

5. History
• Schwender(1867-68):- Helotism
• Anton von De Bary(1887):-Symbiosis
• Reinke(1896):-Mutualism
• Elenkin(1902):-Endosaprophytism
• Awasthi:-Poly symbiosis

6. Habitat
• Lichen grow in the presence of sufficient moisture , cold
temperature , direct sunlight and pure atmosphere .
• On leaves
• Tree trunks
• Old logs
• Floor of forest
• On rocks
• Some lichens are cushion – like masses on bare rocks in
extremely cold regions of arctic zones .
• Some in tropical and subtropical rain forests .
• Most lichen grow in eastern Himalayas than in the western
Himalayas .
• Darjeeling , Gangtok , and in Sikkim .

7. Classification
• Based on their growth
1. Crustose :- It is a lichen that sticks tight to the
substance on which it is growing on. As the name
suggests, it is crusty and even forms a crust on
the substrate it is growing.
2. Fruticose :- It looks like a little branching shrub
such as a miniature leafless tree. It looks similar
to a bushy coral . It grows on rocks, trees and
soils. The word fruticose has a latin origin which
means a bush or shrub.
3. Foliose :- It consists of a leafy shape structure. It
can be easily removed from the surface on which
it grows.

8. • Based on their habitat
1. Lignicolous :- It is a term used to
describe a person who has these
lichens can be found in the woods.
2. Corticolous :- They are those that
live on the bark of trees.
3. Saxicolous:- They are those that live
on stones or rocks.
4. Terricolous:- These grow on soil and
are thus referred to as terrestrial
lichens.

9. • Based on their internal structure
1. Heteromerous lichens
2. Homoiomerous lichens

10. • Based on their fungal partner
1. Ascolichens
2. Basidiolichens
3. Hymenolichens

11. Nature of association
• They are commonly recognized as a
symbiotic association of a fungus and a
chlorophyll containing partner , either
green algae or cynobacteria , or both.
• The fungus provides a suitable habitat
for the partner, which provides
photosynthetically fixed carbon as
energy source for the system.

12. Composition
Lichen is composed of mainly two component:-
component
Fungal component Algal component
a) Basidiomycetes
:-Parasol mushroom
b) Ascomycetous
:-Panicilium
a) Myxophyceae
:-Blue-Green algae
b) Chlorophyceae
:-Green algae

13. Structure of lichen
 The majority of the lichen thallus is comprised
of fungal filaments called the medulla.
 It is made of fungal cells that are loosely
packed in the middle of the lichen thallus,
have thin cell wall and are threadlike
1. Thallus
2. Upper cortex
3. Algal zone
4. Medulla
5. Lower cortex
6. Rhizine
Some of terminology:-

14. Reproduction
1. vegetative
2. Sexually
3. Asexual spore

15. Vegetative Reproduction
In which mainly two methods are include
1. Fragmentation
2. Isidia and soredia

16. Sexual reproduction
 In ascolichens the fungus belongs to
ascomycetes and the sexual
reproduction results in the
formation of apothecia or
perithecia.
 These fruiting bodies are small cup
like or disc like .

17. Asexual spore
 Hyphae of few lichens break up
and germinate into new fungal
hyphae.
 Many lichens produce large
structure, pycniospores, within
flask shaped pycnia.
 These structure act as male
gametes are knowns as
spermatia and spermagonia.

18. ECONONICAL IMPORTANCE
There are some of the importance of the lichen
are given below:-
1. Food for humans and animals
2. Medicinal importance
3. Chemical use
4. Role in nitrogen fixation
5. Biodegradation
6. Use as a dye
7. Antibiotic metabolites
8. Traditional medicine

19. 1. Food for humans and animals
Cetraria islandia fremoontii

20. 2. Medical importance
Peltigera canina Lobaria pulmonaria

21. 3.Chemical use
Rocella

22. 4.Role in nitrogen fixation
cynobacteria
This Photo by Unknown Author is licensed under CC
BY

23. 5.Biodegradation
Permelia perlata
This Photo by Unknown Author is licensed under CC BY-SA

24. 6.Use as a dye
lecanora
This Photo by Unknown Author is licensed under CC BY

25. 7.Antibiotic metabolites
Usnea longissima
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26. 8.Traditinal medicine
Pussila
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27. Lichen as bioindicator
• Lichen can indicate the pollutants in
environment.
• If air is very badly polluted with sulfur dioxide
there may be no lichen present , just green algae
may be found.
• If the air is clean then shrubby , hairy and leafy
lichens become abundant.
• Lichen receive all the nutrients from the
atmosphere, that’s why it is sensitive to air
pollution.
• This is the reason lichens are widely called as
environment indicators , pollution indicators or
bio-indicators.
This
Photo
by
Unknown
Author
is
licensed
under
CC
BY-SA

28.  Lichenometry
• Lichenometry is a geomorphic dating
methods that uses lichen growth to
determine the age of exposed rock , based
on a presumed specific rate of increase in
radial size over time .
• Measuring the diameter of the largest
lichen of a species on a rock surface can
therefore be used to determine the length
of time the rock has been exposed.