1. Lichens: General Characteristics, Thallus
Organization & Reproduction
Presented to:
PROF. DR. ABDUL NASIR KHALID
Presented by:
Fauzia Razzaq
Mphill-13 (Semester-I)
Subject: Mycosymbiosis
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2. Lichens: General characters
Introduction
Discovery and Distribution
Components of Lichen Thallus
Nature of Association
Classification of lichens:
Based on habitat
Based on group of fungal partner
Based on Thallus Morphology
Based on distribution of algal and fungal component in the
Thallus
Lichens reproduction
Economic importance of lichens
Some Lichens that reported from Pakistan
Conclusion
References
Contents
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3. LICHENS: Introduction
Lichen is an association of a fungus (mycobiont) and a green alga
or cyanobacterium (photobiont)’ (Kirk et al., 2001), ‘resulting in
a stable thallus of specific structure’ (Ahmadjian, 1993)
developed.
The ‘vegetative’ part of the lichen is the thallus, and this
can develop into a morphologically diverse range of
structures: multiply branched tufts, flat, leaf-like
structures, filamentous structures, aggregations of tiny
plates, thin crusts, layers of powdery granules, or hardly
any visible thallus at all.
3
7. The unicellular or filamentous
photobiont cells are collectively called
the INHABITANT because they are
located inside the lichen thallus.
The fungal partner usually contributes
most of the biomass to this symbiosis,
including the external surface, termed as
EXHABITNT.
LICHENS: General Characters
Dual nature of
lichens.
First hinted at by de Bary
(1866).
Clearly recognized by
Schwendener (1867).
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9. • Estimated worldwide
total of some 20,000
species of lichenized
fungi.
• 410 lichens reported
from Pakistan.
• Only about 100 species (40
genera) of photobionts are
known.
• Ability to survive extreme
temperatures, high solar
irradiation and other
adverse conditions.
• Grow wherever the
air is clean and
INDICATORS OF
POLLUTION.
(Lobaria pulmonaria).
9
LICHENS: General Characters
10. Lobaria pulmonaria as pollution indicator https://https://www.britishlichensociety.org.uk 10
11. Mycobiont:
Most lichenized fungi (>98%)
belong to the Euascomycetes, with only a
few imperfect fungi and some 20 species
of Basidiomycota also entering this type
of symbiosis.
Photobiont:
Common photobiont genera are the green
algae Trebouxia (found in about 50% of all lichens)
and Trentepohlia, and the cyanobacterium Nostoc.
About 85% of lichenized fungi have a green algal
photobiont, and 10% are associated with a
cyanobacterium.
Components of Lichen Thallus
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13. Classification
Based on Habitat
Based on Group of Fungal Partner
Based on Thallus Morphology
Based on Distribution of Algal and
Fungal Component in the Thallus
Classification of Lichens
13
14. Saxicolous:
Grow on stones or rocks.
Dermatocarpon,
Xanthoria, Verrucaria.
Corticolous:
Grow on bark of trees
e.g., Grpahis, Usnea,
Parmelia.
Follicolous:
Lichen growing on
leaves.
Terricolous: Grow on
soil (terrestrial) e.g.,
Cladonia florekeana,
Lecidea, Collema
Lignicolous:
Grow directly on wood
e.g., Calicium
Marine:
Grow on siliceous
rocky shores of sea e.g.,
Caloplaca, Verrucaria.
Lichens are divided into Various Categories on the basis of their Habitat
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17. Ascolichens:
Fungus belongs to
Ascomycetes.
Reproductions similar to
ascomycetes produce
ascus and ascospores.
It is further divided into
two series depending on
the fruiting body.
Basidiolichens:
Fungus belongs to
Basidiomycetes.
Reproduce by basidia and
basidiospores. There are
only 3 genera which
belong to Basidiolichens.
These are: Cora, Corella,
Dictyonema.
Lichen Imperfectae:
Fungus belongs to
Deuteromycetes lichens
are also known as
imperfect lichens.
Classification of Lichens based on Group of Fungal Partner
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19. Foliose Lichen
• The thallus generally forms flat, leaf-like lobes,
with differentiated layers of tissue, the upper
and lower cortices, forming the upper and
lower surfaces.
• The lobes are commonly, but not always,
appressed to the substrate surface, but can be
lifted away. The lower cortex is often
differently coloured, frequently brown or black
and usually bears rhizines.
Parmotrema perlatum upper and
lower surfaces.
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20. Foliose Lichen: Systematics
The family Parmeliaceae (order Lecanorales) contains a substantial
proportion of the foliose species, including such genera
as Parmelia, Evernia, Hypotrachyna, Melanelixia, Parmotrema and
numerous others mostly once placed in a larger concept of Parmelia.
The order Peltigerales contains several families of foliose lichens,
including the Lobariaceae (Lobaria, the tree lungworts, and allied genera),
the Pannariaceae (with, e.g., Degelia), and
the Peltigeraceae (with Peltigera, the dog lichens, and Solorina).
The family Umbilicariaceae (sole family of the order: Umbilicariales)
contains Umbilicaria and Lasallia. Smith et al. (2009).
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22. Fruiticose Lichen
The thallus is extended up into a tufted or pendant branched structure, the
branches being covered by a single cortex.
In fruticose lichens with flattened branches, e.g. Ramalina spp., the cortex
extends round both surfaces of the branch. Consequently, they differ from
foliose lichens with branched, aerial lobes such as Evernia.
Ramalina polymorpha
Ramalinaceae
Usnea subfloridana,
Parmeliaceae
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23. Fruiticose Lichen: Systematics
Stereocaulon contains richly branched, fruticose species.
The family Cladoniaceae (order Lecanorales) contains predominantly
fruticose lichens (or lichens commonly described as such),
including Pycnothelia and Cladonia, but the primary thallus is crustose
(if only briefly so) or squamulose.
Generally, individual fruticose genera are most closely related to genera
with other growth forms, e.g. Roccella is grouped with crustose genera in
family Roccellaceae (order Arthoniales), Alectoria, Bryoria and Usnea are
grouped with numerous foliose genera in the
family Parmeliaceae (order Lecanorales), Stereocaulon family Stereocaul
aceae (order Lecanorales), Teloschistes is grouped with crustose,
squamulose and foliose genera in the
family Teloschistaceae (order Teloschistales). There is no generally
fruticose line of evolution.
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24. Squamulose Lichen
In squamulose lichens, the thallus is
composed of usually small, flat, usually
massed, often overlapping scales .
They differ anatomically from the
smaller foliose lichens in that the
squamules do not have a lower cortex,
or at most it is weakly differentiated,
rhizoidal hyphae may be produced.
Squamarina cartilaginea: squamulose
thalli. 24
25. Squamulose Lichen: Systematics
Cladonia subgenus Cladonia,family Cladoniaceae (order Lecanorales), have a
squamulose primary thallus.
Squamarina is doubtfully placed with both crustose and fruticose genera in the
family Ramalinaceae (order Lecanorales); several squamulose genera such
as Protopannaria and Psoroma are grouped with foliose genera in the
family Pannariaceae (order Peltigerales); Catapyrenium, Dermatocarpon, Norm
andina and Placidium (all with perithecial fruiting bodies) are allied to the
well-known crustose genus Verrucaria .
The basidiomycete lichen, Lichenomphalia hudsoniana, a toadstool allied to
the waxcaps (Hygrocybe) in family Hygrophoraceae (order Agaricales) also has
a thallus composed of squamules.
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27. Crustose Lichen
The thallus forms a crust over the substrate and is firmly attached to it.
There is an upper cortex, at least in early development, but no lower cortex
and the medulla is in direct contact with the substrate and commonly grows
into it to some extent.
Ophioparma ventosa, fertile, crustose thallus
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28. Crustose Lichen: Systematics
Probably all major groups of lichenised fungi include simple, crustose forms.
Some of the better known genera include:
Arthonia, in the family Arthoniaceae (order Arthoniales),
Verrucaria in the family Verrucariaceae (order Verrucariales),
Acarospora in the family Acarosporaceae (order Acarosporales),
Diploschistes, Graphis and other graphoid genera in the
family Graphidaceae (order Ostropales)
Aspicilia in the family Megasporaceae (order Pertusariales),
Ochrolechia in the family Ochrolechiaceae (order Pertusariales),
Pertusaria in the family Pertusariaceae (order Pertusariales),
Lecanora and Lecidella in the family Lecanoraceae (order Lecanorales),
Bacidia in the family Ramalinaceae (order Lecanorales)
Rinodina in the family Physciaceae (order Teloschistales), and
Caloplaca in the family Teloschistaceae (order Teloschistales), though many
of the last would be better described as "crustose-placodioid".
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29. Lichen mosaic on iron-rich rock:
Species of crustose genera, including Rhizocarpon, Porpidia, Lecanora and Lecidea, are
growing together on the rock surface 29
30. Placodioid lichens (incl. 'crustose-placodioid', 'squamulose-placodioid')
The thallus is generally
crustose, but the margin
extends into distinct,
radiating lobes, which
still lack a lower cortex
but which may not
always be so firmly
attached to the substrate.
This is really a variant of
"crustose" and many
individual species may be
simply crustose or may
alternatively become
placodioid.
Systematics:
Numerous species of Caloplaca, in the
family Teloschistaceae (order Teloschistales),
have variable development of marginal
lobes, and some, such as Caloplaca
thallincola, , normally have these well
developed. Many of these can be described as
"crustose-placodioid".
The large genus Lecanora, in the
family Lecanoraceae (order Lecanorales), is
predominantly crustose, but a very few
species are placodioid. Fulgensia, is grouped
with crustose, foliose and fruticose genera in
family Teloschistaceae (order Teloschistales).
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31. Caloplaca thallincola
This species is noted for its characteristic, long, radiating lobes, giving the thallus a wheel-
like appearance. However, on rough rock surfaces, the lobes may be poorly formed or
sometimes even missing, making the thallus simply crustose with dispersed areoles.
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32. Leprose Lichen
In leprose lichens the thallus surface is
composed of granules containing algal
cells and fungal hyphae with no
overlying cortex, even during early
stages. There can be a thin, underlying
medulla but even this may be missing,
the lichen then being a film of granules
with little, if any, further fungal matrix.
Common examples include
• Dirina massiliensis
• Lecanora expallens
• Porpidia tuberculosa.
The thallus is diffuse and powdery; in
this species there is no underlying
medulla. Lepraria incana.
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33. Leprose Lichen: Systematics
The best known and certainly most frequent genus of leprose lichens
is Lepraria, allied to the fruticose genus, Stereocaulon, and placed in the
family Stereocaulaceae (order Lecanorales).
Leprocaulon, with a leprose primary thallus resembling a Lepraria but then
producing small, delicate branches (pseudopodetia), has also been placed in
the Stereocaulaceae, but its correct taxonomic placement is uncertain.
The family Pilocarpaceae (order Lecanorales) contains several lichen genera
with reduced thalli that vary from crustose to granular in Micarea to granular
to leprose and lacking a cortex in Psilolechia, Byssoloma and Fellhanera.
The family Coniocybaceae, containing the 'pin-lichen'
genera Chaenotheca and Sclerophora, constitutes another group of lichens of
uncertain taxonomic relationships.
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34. Filamentous Lichen
In filamentous lichens, the fungal
hyphae form sheaths around
filaments of the alga
(Trentepohlia or trichome-forming
cyanobacteria).
The lichen retains the morphology
of the algal component, though
will generally be a little more
robust and generally darker in
colour.
In cyanolichens, e.g. Ephebe
lanata, the lichen may actually
differ little in appearance from the
free-living cyanobacterium
(Stigonema in the case of Ephebe). Cystocoleus ebeneus, macroscopic and
microscopic views 34
35. Filamentous Lichen: Systematics
Relatively few lichens can be described as filamentous, and as with other
thallus types, the fungi belong to several different orders and
classes. Cystocoleus and Racodium are evidently related and belong to the
order Capnodiales, but in Smith et al. (op. cit.) they are not assigned to any
family within the order.
Ephebe lanata (Lichinaceae) Polychidium muscicola (Massalongaceae)
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36. Lichens with no visible thallus
Sometimes, lichen fruiting bodies
may be seen on a substrate and yet
no thallus is visible. This may be
because:
The thallus is evanescent (soon
disappearing).
The thallus is immersed (has
developed within the surface of
the substrate, e.g. is endolithic).
The lichen exists as hyphae (with
minimal photobiont) within the
thallus of another lichen, i.e. is
lichenicolous.
Acrocordia conoidea: An example of
a pyrenocarpous lichen occurring
embedded in tiny pits in the
substrate surface, in this case
limestone.
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37. Lichens with no visible thallus: Systematics
Pyrenocarpous lichens frequently have no visible thallus, so this
phenomenon is more likely to be seen, e.g., in the order Pyrenulales
or in genera of uncertain systematic position such
as Collemopsidium in the family Xanthopyreniaceae, not assigned to
any order in Smith et al. (op. cit.).
The large genus Thelocarpon, consisting of very inconspicuous
species with the thallus usually no more than an algal sheath around
the perithecia, is placed in the family Thelocarpaceae, again not
assigned to any order.
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41. Vegetative Reproduction
Vegetative Propagules:
Soridia:
• Small clumps of hyphae enclosing
a few algal cells.
• Produced over the entire surface
of the thallus or in differentiated
structures called soralia.
Isidia:
Larger, upright cylindrical
structures which contain both
symbionts.
Become detached and then
function as vegetative Propagules
such as Cladonia.
41
https://www.google.com/url%2FHarshitaBh
awsar%2Fbasics-of-lichens
42. Asexual Reproduction
Flasked shaped pycnidium with an ostiole is formed.
Pycnidiospores formed on inner layer of pycnidium.
Spores after dispersal form individul fungal colonies, when come in contact
with suitable algal partner form lichens.
https://image.slidesharecdn.com/physcia-180201154102/95/physcia-16-
638.jpg?cb=1517500024
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43. Economic Importance of Lichen
Ecological significance
Pioneer colonizers
Role in environmental pollution
Food and Fodder (Cladonia rangiferina)
Source of Medicines
In Industry
Tanning and dyeing
Brewing and distillation
Minerals
Cosmetics and perfumes (Ramilina and Evernia)
Natural products
Poison from Lichens
Harmful Aspects
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46. Some Lichens that reported from Pakistan
Bacidina margallensis M. Fatima, K. Habib & A. N. Khalid
Bacidina iqbalii K. Habib & A. N. Khalid
Lecidea aptrootii, M. Khan, A.N. Khalid, H. T. Lumbsch
Lecidella carpathica Korb
Lecidella patavina (A.Massal.) Knoph & Leuckert
Lecidella stigmatea (Ach.) Hertel & Leuckert
Punctelia borreri (Sm.) Krog
Punctelia subrudecta (Nyl.) Krog
Peltigera elisabethae Gyeln.
Xanthoria sogdiana S.Y. Kondr. & Karnefelt,
Lecidella tumidula (A.Massal.) Knoph & Leuckert,
Pertusaria australis (Pertusariaceae)
Varicellaria hemisphaerica (Ochrolechiaceae)
46
47. Conclusion
• Lichens are symbiotic associations of algae and fungi characterized by low
growth rates and nutrient requirements that enable them to play the role of
pioneer vegetation in the colonization of fresh rocks.
• Estimated worldwide total of some 20,000 species of lichenized fungi. 410
species reported from Pakistan.
• Only about 100 species (40 genera) of photobionts are known.
• Grow wherever the air is clean and indicators of pollution such as Lobaria
pulmonaria.
• Extensive surveys are required to fully explore lichen flora and evaluate its
ecological role.
47
48. References
Introduction to Fungi. Third Edition. By John Webster and ,
Roland Weber. Cambridge and New York: Cambridge University Press.
The Fifth Kingdom Third Edition. By Bryce Kendrick.
Fatima, M., Habib, K., Czarnota, P., & Khalid, A. N. (2021). Two new
Bacidina species (Lecanorales, Ascomycota) from Pakistan. Folia
Cryptogamica Estonica, 58, 25-34.
Habib, K., Imran, A., Khalid, A. N., & Fiaz, M. (2017). Some new
records of lichens from Hunza valley, Pakistan. Pakistan Journal of
Botany, 49(6), 2475-2482.
Habib, K., Zulfiqar, R., & Khalid, A. N. (2020). Additions to the
lichenized order Pertusariales (lichenized Ascomycetes) in Pakistan. Nova
Hedwigia, 219-229.
Khan, M., Khalid, A. N., & Lumbsch, H. T. (2018). A new species of
Lecidea (Lecanorales, Ascomycota) from Pakistan. MycoKeys, (38), 25.
www.lichens.lastdragon.org
www.biologydiscussion.com
References
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