Basics of lichens. introduction, distribution, structure, use.

1. Presented by:-
Harshita Bhawsar
School Of Life sciences(SLS)
Central University of Gujarat

2.  Lichens
• Sytematics
• Habitat
• Types of lichens
• Structure
• Lichen chemistry
• Identification of lichens
• Lichen importances

3.  Lichens is the symbiotic organism composed of a fungal
partner (the mycobiont) with a photosynthetic partner(the
photobiont) which can be either green algae or cynobacteria.
 That intimate association of these two microorganisms results
in the formation of a macro-organism, The Lichen.
 This true nature of lichens was first identified by Swiss
Botanist Simon Schwendener.
 It appear to be a single organism. Therefore, also known as
composite or dual organism
 Lichen is quite different from the original organisms.
 They are in mutual association where both the organisms get
benefited.

4.  The mycobiont provides the necessary substratum
and also aids in the assimilation of moisture, micro
and macronutrients to the photibiont partner for
grow and in turn, it receives the carbohydrates for
metabolic activity
 They form an integral and important part of an
ecosystem.

5.  They are classified under Fungi. As the mycobiont is unique
and usually dominates in this symbiosis association.
 Largely the fungal partners belong to Ascomycota (cup fungi)
but, few of them belongs to Basidomycetes (Mushroom) or
Deuteromycetes (fungi imperfect).
 And the photobiont partner is-
 Mostly a Green alga belongs to class Chlorophyceae (85%),
eg:- Verrucaria mucosa
 Or a cyanobacterium belongs to Cyanophyceae (10%), eg:-
Sticta hypodira
 Or sometimes it posses both (approx 5%), eg:-
Pseudocyphellaria rufovirescens
http://www.ohiomosslichen.org/Lichenology-101.pdf

6.  One of the fascinating aspects of lichen biology is the ability
of these organisms to occupy habitats that would be totally in
inhospitable to other organisms.
 They dominant around 8% of the world’s total land.
 They have the ability to absorb and retain water from air or
dew and become metabolically active within a few minutes,
whereas inversely in sunny conditions, they lose water and
become dry and crisp within an hour, this vesatility make
them possible to grow in any environments.
 They are found on bark,leaves, trees (as epiphytes), on
exposed surfaces like soil, rocks, masonery and cemetery
headstones.

7.  They often found in extreme environments where other
organisms are sparse like arctic, antarctic, alpines, desert .
 In India Western Ghat together with Eastern and Western
Himalaya regions represent rich lichen diversity areas.
 India represent 2532 species under 324 genera and 78
families including 541 endemic (21.3 %) species.
http://bsienvis.nic.in/Database/LichensinIndia_22590.aspx?format=Print

8. 1. Corticolous- Grows on tree bark.
•The bark help lichens in
trapping their spores.
•Also to retains moisture
for longer duration
•It contain mostly
fruticose and foliose
species.
•Eg:- Usnea.
TYPES

9. 2. Foliicolous ( or epiphyllous)
 Grows on the leaves of
vascular plants.
3. Saxicolous
 That grows on rock.
 It vary according to the
rock type.
Eg:- Verrucaria
•Epiphylls (a general term
for organisms
Living on leaves).
•Found in wet or moist,
high humid, foggy tropical
and subtropical forests.
•Eg:- Strigula

10. 4. Terricolous
•Grows on ground or soil .
•Often form a dominant component of the ground vegetation in
the extreme environments
•It plays a vital role in maintenance and ecological stability of the
soil crusts with reference to their physical stability, hydrology and
growth of soil microflora.
•Eg:- Bryoria

11. 5. Musicolous
• It grows on mosses.
• They prefer the bushy mosses which are efficient in trapping
liches propagules.
• The hygroscopic nature of the mosses provides better water
relation and microclimatic niche to the lichens growing on
them.
• Eg:- Cladonia

12. They are mainly classified on the basis of their
morphology and size into 3 major categories
namely:-
1. Crustose
• They are crust like.
• Tightly attached to the
substrate.
• Have only upper surface.
• They are microlichens.

13. 2. Foliose
• They are usually flat and leaf
like and can be loosely to tightly
attached.
• They have an upper
and lower surface.
• They are called macrolichens.
3. Fruticose
•They are shrubby or bushy,
sometimes they hang down.
• Most of them don`t have any
upper and lower surface but are
often round in cross section.
•They are also called
macrolichens.

14. 1. Squamulose- They are the intermediate between crustose
and foliose. They are small and leafy with loose attachments
to the substrate. They are composed of small and overlapping
"scales" called squamule.
2. Leprose- It has powdery and granular surface. They don’t
have any cortex, only have a weak kind of medulla.
3. Dimorphic :- Single thallus has the characters of both foliose/
squamulose and fruticose lichens. They have leaf and erect
stem like structure.
4. Placodioid:- Lichen thallus is closely attached to the
substratum at the center , free at margin and lacking
rhizines.

15.  After association, both the phycobiont and mycobiont
components lose their individuality and the lichen behaves as
a single organism, both morphologically and physiologically.
 In this symbiosis mycobiont is the exhabitant and photobiont
is the inhabitant.
 The main plant body part is Thallus, a vegetative portion.
 In thallus the mycobiont predominates with 90% of the
thallus volume and provides shape, structure and colour to
the lichen with partial contribution from photobiont.
Thallus Structure
 The thallus of the lichen is divided into three layers :-
1. Cortex
2. Algal layer (Photobiont)
3. Medulla

16. 1. Cortex Layer
• It is band of compacted fungal hyphae.
• Coxtex serve as a protecting layer and consist of upper and
lower cortex layer.
• It is 10-40µm thick with several layers of cells
• The upper cortex layer protect the tissues beneath and also
supplies mechanical support to prevent the breaking of the
thallus due to winds or other external forces.
• The lower cortex layer present in some ,is same as upper
cortex layer and possess rhizoids.
2. Algal Layer (Photobiont)
• Algal cells are present which are completely surrounded by
fungal tissue.

17. • This layer is responsible for by photosynthesis and providing
food.
• It makes a great contribution in thallus colour.
3.Medulla
• It is a loose weave of fungal hyphae.
• Lichen thallus is majorly consist of medulla, may be 500µm
thick.

18. Lichen thallus seen under microscope http://wgbis.ces.iisc.ernet.in/biodiversity/sahyadri_enews/newsletter/issue34/index.htm
(a) Homoimerous thallus
https://link.springer.com/chapter/10.1007%2F978-3-319-13374-4_1
(b) Heteromerous thallus

19. 1. Crustose Species
2. Foliose species
3. Fruticose Species
Concentric photobiont
and medulla
http://www.anbg.gov.au/lichen/form-structure.html

20. Other structures present on upper and lower surfaces
of the thallus.
1. Rhizines:- Rhiz- a root /something anchoring into the
ground.
• They are compacted strands of colourless or blackened
hyphae that originate largely from the lower cortex and
anchor the thallus to the substrate.
• Simplest rhizines are unbranched while branched are of 2
type:- Squarrose= Perpendicular and bottlebrush shape and
dichotomous .
Rhizines

21. 2. Cillia :- They are hair like thalline appendages, decolourized
strands of hyphae that originate along the lobe margins or on
the exciples(rim) of apothecium.
• Cillia appear to be related to the rhizines and are restricted to
foliose genera mostly.
3. Pores :- Foliose lichens produce pores on the lower surface
of the thallus which help in gas exchange similar to that of
stomata on the leaves of higher plants.

22. • The most highly specialized pores are called Cyphellae.
• Psuedocyphellae- Undiffrentiated pores, appears dot- like on
the outer surface, caused when there is a break in the cortex
and the medullary hyphae reach the surface.

23. 4. Maculae
In lichens photobiont layer does contribute to the overall
colour of the thallus, an area free of photobiont will show as a
paler spot or line on the thallus. Such spots or lines, usually
irregular in shape, are called maculae.
http://wgbis.ces.iisc.ernet.in/biodiversity/sahyadri_enews/newsletter/issue34/index.htm

24. Vegetative reproductive structure
 The vegetative reproduction in lichens is achieved by the
development of special propagules which are unique to
lichens.
 Vegetative propagules (diaspores) are lichenized structures in
which algal and fungal components together act as separable
autonomous subunits of the thallus.
 Vegetative propagules of lichens are:- Soredia, Isidia, and
various thalline structures such as squamules, lobules,
phyllidia, blastidia, fragments or even the whole thallus.
 And the commonest among them are soredia and isidia.

25. 1.Soredia:- Are cluster of algal cells wrapped into the fungal
hyphae. It originate in the medulla and algal layer and erupt
through pores or cracks in the cortex. It can grow anywhere
on the thallus but sometimes soredium production is
confined to delimited area called Soralia .
• They are classified as marginal and laminal according to their
position and farinose and granular according to their fineness.
• It detaches from the thallus and are carried away by wind and
upon falling on a substrate it germinates and give rise to new
thallus.

28. 2.Isidia:- Are stalked,branched or unbranched, outgrowths
form on the thallus surface. It consists of algal cells and fungal
hyphae covered by cortex.
 When it detaches from the parent and give rise to the new
thallus. Or if it remains in the parent thallus it will increase
the photosynthetic efficiency by increasing the surface area.
 Fruticose and foliose produce isidia but it is much rare in
crustose.

30.  Only fungal partner reproduce sexually, and the new fungus
that grows must have to find it an alga partner.
 As a result, asexual reproduction is more beneficiary than
sexual reproduction in the lichen world.
1.Apothecia:- Fruiting body of the Ascomycetes,[and it is
basidiocarp in Basidomycetes] typically open disc or cup-
shaped structures.
 The hymenium surface of apothecium is referred as the disc
and it is composed of asci interspersed with sterile hyphae.

31. In some genera the
apothecia are narrow and
elongated and are then
termed as Lirellae

32. 2. Perithecium:- It is small fungal fruiting body which looks
like hemispherical black pimple. These spores are released
through the pore on upper surface of thallus called as ostiole.
Strigula subtilissima On leave
http://www.anbg.gov.au/lichen/form-structure-reproduction.html

33. 3. Pcynidia:- Are flask shaped structures embedded in the
thallus . They produce hundreds of little flecks of fungal
hyphae called conidia.
• Conidia function as male spermatia, fusing with the “female”
nucleus in the asci.
• Conidia can also function as asexual fungal spores by falling
onto the substratum, germinating, encountering a suitable
alga and forming lichen.

34. Life cycle of lichens

35.  Chemical constituent of lichen are categorized into 2 main
class:- primary and secondary metabolites.
 Primary metabolites
 They are intracellular product which are directly involved in
metabolic process of lichens such as growth, development
and reproduction.
 They includes proteins,vitamines, polysaccharides and are
bound to cell wall and protoplast. They are often water
soluble.
 They are are non specific and either of algal or fungi origin or
both.

36.  Secondary metabolites
 They are of fungal origin. And produced by utilizing primary
metabolites through 3 major pathways:-
1. Acetate-polymalonate pathway
2. Shikmic acid pathway
3. Melvonic acid pathway
 They are not directly involved in metabolism of lichens. They
are the byproduct of primary metabolism and biosynthetic
pathway.
 They act as storage substance and have ecological important
role.
 Seconday metabolites deposited on the surface of the
hyphae rather then cell, hence also called extra cellular
compounds.

37.  They are insoluble in water and can be extracted by organic
solvent.
 Lichens synthesize around more then 1000 secondary
metabolites, many of which are unique.
 Most of them are usnic acid, phenolic compounds,
anthraquinones, dibenzofurans, depsides, depsidones,
depsones, triterpenes, gamma lactones and pulvinic acid
derivatives.
 They shows multiple biological activity:- antiviral, antibiotic,
antitumor, allergenic, plant growth inhibitory and enzyme
inhibitory.
 Certain lichen metabolites also have the ability to reduce the
mutagenicity of chemical mutagens, that has attracted
moderate attention.

38. Biosynthetic pathways of lichen secondary metabolites

39. 1. Morphological identification
2. Biochemically identification
3. Molecular identification

40. The lichen are morphological segregated according to their
growth form.
 Type of thallus:- Crustose, Foliose, Fruticose, Squamulose,
Dimorphic, Leprose.
 Shape:- irregular or circular
1. Upper surface
 Thallus texture:- smooth, rough, warty, presence of finger like
projections (isidia), granular powder in groups (soredia), black
dots (pycnidia) and whitish decorticated areas
(pseudocyphellae) .
 Branching:- isotomous, anisotomous, pseudomonopodial
2. Morphology of fruiting bodies
 Apothecia shape:- rounded or streched or lirellate
 Attachment, color,size and color of margin and disc.

41. 3. Lower surface
 Lower surface of foliose lichen can be seen.
 The color of lower surface, presence of any pores, presence
or absence of rihizines, their distribution.
Anatomically identification
 Anatomy of thallus and fruiting body are examined to identify.
 Anatomy of thallus:- To see thickness of various layers, type of
algae and its distribution (stratified or uniform) and
arrangment of fungal hyphae.
 Anatomy of fruiting bodies:- types of spore, color, shape, size,
number of spores in sac, color of sac wall, presence/ absence
of crystals and algal cells in wall, color and height of the layers
within the ascocarps.

42.  Lichens produced 1000s of secondary metabolites. Most of
them are unique to the lichen and not available in any other
plant groups.
 These substances act as an important character for
identification of lichens.
 It can be identified by performing certain tests:-
1. Colour spot test
2. Microcrystalography
3. TLC
4. HPLC

43.  This test has been used universally as rapid, non-specific means
for detecting the presence of certain unspecified lichen
substances
 Lichens components react with certain test chemicals applied on it
and impart a color change to the thallus part, which will assist in
the identification of the substances.
1.K Test (aq. Potassium hydroxide)
10% aq.KOH solution, Perform on either upper cortex or medulla. It
turns yellow then red with o-hydroxy aromatic aldehyde. And
turn bright red to purple with anthraquinone pigment.
2. C test (calcium hypochlorite or bleach)
Saturated aq. Ca(OCl)2 or Na(OCl)2, Perform on medulla. It turns
red with m-hydroxy phenol, except for those substituted
between hydroxy group with a –CHO and –CO2H. And turns
green with dihydroxy dibenzofuran.

44. 3. Pd test:- aqueous solution of paraphenyldiamine
5% alcohlic solution is use, it perform on medulla. It turns
yellow, orange and red with aromatic aldehydes.
It is most safely used as Steiner’s solution, a stable form of this
stain, made by dissolving 1 g of Pd, 10 g of sodium sulphite,
and 0.5 ml of detergent in 100 ml of water
4. KC test
10% aq KOH followed by saturated Ca(OCl)2. It turns yellow with
usnic acid,turns blue with dihydroxy dibenzofuran and turns
red with depsides and depsidones which undergo rapid
hydrolysis to yeild a m-dihydroxy phenolic moeity.
5. I test
 It is used in the form of Lugol’s solution, aid microscopical
examination of asci. It is made by dissolving 0.5 g of iodine
and 1.5 g of potassium iodide in 100 ml of distilled water.


45.  Some of the secondary metabolites form characteristic
crystals when a crystallising reagent is added and gently
warmed.
 A small piece of thallus in placed on the slide and its chemical
extracted on the slide by dropping acetone over it.
 It gives a concentric white rings of crystals around the thallus
piece.
 After this the drop of crystallizing agent is added over the it
to enhance the crystal formation.
 And lastly it is gently heated by placing cover slip on it and
then allowed to cool to form crystal.

46.  Then slide observed under microscope and lichen susbtance
identified according to crystal shape and size.
 Various crystalizing agents used in microcrystallography
 G.E:- Glycerine-acetic acid, 1:3
 G.A.W:- Glycerine-alcohol-water, 1:1:1
 G.A.Ot:- glycerine-alcohol-o-toluidine, 2:2:1
 G.A.An:- Glycerine-alcohol-aniline, 2:2:1
 G.A.Q:- Glycerine-alcohol-quinoline, 2:2:1
 It is accurate then the color spot test. But it is difficult to
identify mixture of components and minor components
through it.

47.  Many of the lichens substance is undetectable by previous
methods.
 TLC is simple, relatively inexpensive, speedy method and
helps accurate recognition of secondary metabolites.
 Lichens metabolites get separated as spot on TLC plate.
 The spots are identified as different lichen substances by
noting its colour and measuring the distance moved by it,
with the help of TLC manuals.

48.  HPLC with reversed-phase columns, gradient elution, benzoic
and solorinic acids as standard has become a common
practice to identify lichens substances, which are
unidentifiable in TLC.
 HPLC is quite an expensive method and also not possible to
try on every collected specimen.
 Therefore, the materials initially screened out with TLC and
only few interesting or the specimens with complicated
chemistry should be analyzed through HPLC.

49.  Humans have been exploiting lichens and their substances for
various purposes from last many years.
 Lichen has been majorly used for dyeing stuff and an
important food source for reindeer in the tundra and
subarctic forest since long time.
 It can also be eaten by human in various parts of world.
 Also have been used as many common condiments and
flavoring agent.
 Lichens are used in preparation of perfumes and cosmetics.
 Lichen have bioactive compounds:- antimicrobial, anti-
inflammatory, analgesic, antipyretic, antiproliferative and
cytotoxic activities.

50.  They have the ability to accumulate the metals ions, tiny
particles of rock, soil or any other heavy metal pollutants within
their structure, from the environment in which they live.
 Which helps in monitoring the pollution levels and type of
pollutant emissions around a particular industrial area.
 Thus lichens are considered as Bioindicators of environmental
pollution and used as biomonitors of air quality.
 Lichens may aid in the breakdown of rock into soil.
 And some lichens (with cyanobacteria) can fix nitrogen and
increases productivity .

51. 1. http://wgbis.ces.iisc.ernet.in/biodiversity/sahyadri_enews/ne
wsletter/issue16/identify.htm#5
2. http://wgbis.ces.iisc.ernet.in/biodiversity/sahyadri_enews/ne
wsletter/issue34/index.htm
3. Nayaka, S. (2014). Methods and techniques in collection,
preservation and identification of lichens. Plant Taxonomy
and Biosystematics-Classical and Modern Methods. New
India Publishing Agency, New Delhi, 101-128.
4. http://www.anbg.gov.au/lichen/form-structure.html
5. http://www.britishlichensociety.org.uk/identification/chemic
al-tests
6. http://shodhganga.inflibnet.ac.in/bitstream/10603/150447/1
1/11_chapter%203.pdf
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ch100.pdf
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