Lichens are a symbiotic relationship between fungi and algae or cyanobacteria. The algae or cyanobacteria conduct photosynthesis to produce food, while the fungal partner provides structure and absorbs water and minerals. Lichens grow slowly and can be crustose, foliose, fruticose, or squamulose in morphology. They reproduce asexually through soredia, isidia, or fragmentation, and sexually through ascospores. Lichens produce protective lichen acids and have various uses as food, fodder, dyes, perfumes, and indicators of air pollution due to their sensitivity. They are also useful for dating surfaces in the field of lichenometry.

1. Presented by-
Miss. Varsha Yadav
Lichens

2.  Lichen is derived from the Greek word
‘Leprous’ and refers to medicine used
for treatment of skin diseases
because of their appearance as
peeling skin
 Schwendener –dual nature

4. Where they are?

5. Relationship between
algae and fungus
- Mutualism - both gain benefits
-Algae produce carbohydrates as
food supply
-Fungus with hyphae holds the
structure firmly on substrates and
absorb mineral salts
-Controlled parasitism

6. Photobiont
 Green algae – Trebouxia is a common
genus, found in 75% of lichens in
temperate zone
 Cyanobacteria – Nostoc is a common
genus
 25 genera of algae and 15 of
cyanobacteria found in lichens, 90% of
lichens contain Trebouxia, & 8 %
Nostoc or one other genus

7. Mycobiont
 Most lichenized fungi are Ascomycotina – most
form apothecia, some form perithecia and
pseudothecia.
 12 orders include mostly lichenized members
(Arthoniomycetes , Eurotiomycetes ,
Leucanomycetes , Lichenomycetes )
 Some are Basidiomycotina – Aphyllophorales,
few Agaricales .
 Some are Deuteromycota
 20% of all fungi & 40% of ascomycotina are
lichenised( Krik et al.,2008).

8. In culture what happens ?
Photobiont :
 Trebouxia : produces zoospores
produce gelatinous sheath
: produce gelatinous Nostoc
sheath
Mycobiont :
 Develops into an undifferentiated mass

9. Optional lichenization
 As ecological adaptation (sedin et al .,
2004 )
 Conotrema (lichenizing fungi )
 Strictis ( non –lichenizing )
 Both belongs Leucanoromycetes
(Pezizomycotina ).

10. Thallus morphology
 4 basic types
 Crustose – flattened,
scalelike,
 No lower surface, tightly
bound to substratum

11. Thallus morphology
 Fruticose – branched, strap shaped or
threadlike thallus, upright or hanging

12. Thallus morphology
 Foliose – flattened
branching lobes
loosely attached to
the substratum,
leaflike
 Have upper and
lower surfaces
 Anatomically
similar to
angiosperm leaf.

13. Thallus morphology
 Squamulose – intermediate between
foliose and crustose
 Scales, lobes smaller than in foliose

14. Growth
 Exhibit low growth rates (crustose) –
many grow at rates of 1-4 mm/yr, up to 9
cm/yr (foliose)
 Makes studies difficult
Factors affecting growth
 Light – variable – some prefer low light
intensities, others high
 Temperature – variable
 Moisture – appears to be an important
variable, do not have water absorbing
organs, depend on moisture in air

15. Moisture
 When lichen thallus is wetted, absorbs
water quickly by gelatinous matrix in the
cortex Starts growth process
 As thallus dries, growth process slows
and stops
 Dew and humidity are important sources
of moisture
 Thalli are inactive when dry – only grow
when wetted
 Most of them require low light intensity,
cool temperature & moisture.
 may be responsible for slow growth rate

16. Asexual
reproduction
 Fragmentation
 Soredia - algal
cells enveloped
by hyphae, no
cortex, form
powdery masses
on surface of
thallus, detach
from thallus

18. Isidia – column like
structures with cortex

19. SEM of
Bulbothrix
with isidia

20. Sexual reproduction
 characteristic of fungal symbiont
 Ascospores are discharged, algal cells
are not discharged with them
 Thought that after ascospores
germinate, they make contact with
algal cells

21. Internal structure

22. Hypogymnia Haematomma

23. Perithecia
in
crustose
lichen
Pyrenula
Pseudothecia
of Niebla
Pseudothecia of Melanotheca

24. Lichen acids
 The metabolites (mainly secondary) are
antimycobacterial, antiproliferative,
antiviral, antibiotic, anti-inflammatory,
cytotoxic, analgesic and antipyretic
effects.
 belongs to depsides & depsidones
(which are condensation products of 2-or
3 phenyl carboxilic acids mainly orsellinic
or ß- orsellinic acid held together by ester
linkage

25. Role of lichen acids
 Usnic acid – wide spectrum antibiotic
activity (Shibamoto and Wei, 1984,
Rowe et al., 1991).
 Vulpinic acid exhibited mild antibiotic
activity (Lauterwein et al.,1995).
 These acids inhibited the growth of
Bacillus subtilis, Staphylococcus aureus
and Bacillus magaterium.

26. Lichen acids
 As defense chemicals against attacks by
slugs & other minute animals
 Have good chelating properties (metal
binding )
 Tranlocate substances between partners
 Increase permiability of algal cells
 Stabilize the amount of light reaching the
photobiont layer

27. uses

28. As source of food
 Cetraria islandica was used as food in
Northern Europe and was cooked as
porridge, soup, bread, salad and pudding.
 Bryoria fremoontii were mostly used as
food in times of famine in North America
so they were called famine food.
 In China, lichens are used as food
(Lobaria isidiophra, L.yoshimurae) and
also as health promoting tea (Thamnolia
subuliformis, Lethariella cashmeriana).

29. As fodder
 Cladonia rangiferina in
taundra,
 Cetraria islandica in iceland
 Sps of Lecanora
 Nutritive value is due to lichenin
As initiators of vegetation on rocks
Crustose lichens are primary colonizers

30.  Some lichens known as Earth Flowers
have a strong and distinct odour so they
are smoked along with tobacco used in
summer dances (Curtin, LSM. 1984).
Medicinal properties
 Peltigera canina - hydrophobia
 Parmelia saxatilis - epilepsy
 Lobaria pulmonaria -
lung infections

31. Perfumes & dyes
 The extracts are used to dye wool .
 They are also used in the
manufacture of ‘moss’ and ‘leather’ &
fragrances in perfumes and some
type of soaps (Richardson, D. H. S.
1974)

32. lichenometry
 1st employed by Faegri 1950
 Most accurate when rocks are
lessthan 1000 yrs
 10,000 yrs maximum age
limit (10 % error )
 Mostly used are ascomycetous genera
Rhizocarpon & Xanthoria elegans

33. Lichens are advantage
over vascular plants
As a bioindicator of air
pollution: because they
have no wax &cuticle
to protect cells (inner
structure)
Cortex:
Fungal layer
Algal layer
Medulla

35. Fruticose : The most sensitive
Lichens are differently sensitivity to air pollution

36. Foliose : The
second

37. Crustose :The most resistance

38. Lichen are efficient indicator of
air pollution &aciddeposition.
They are less cost comparing
with expensive equipments.
Appropriate technique should
be developed especially in
developing countries to use
lichens as bio-monitoring of air
Pollution.
Lichens provide warning signal
before severe damages occur
on ecosystem & health.

50. Thankyou