Lichens 2021

LICHENS
1. Introduction of lichens
General features
The lichens are a small group of curious plants with about 18,000 species. They are composite or dual
organisms. For a long time, the lichens were considered as individual plants and were lumped together with
the mosses. In 1867, Simon Schwendener found that the thallus of lichen is composed of two quite
different organisms, a fungus and an alga, forming a self-supporting combination. The fungal
component is called the mycobiont and the algal component is known as the phycobiont. The two live in
intimate association so that they appear to be a single plant. The fungal component forms the bulk of the
lichen thallus. The algal component occupies only a small part comprising about 5-10 percent of the mass
of the thallus. The fungal hyphae form a close network resembling a tissue-like mass with the algal cells
often embedded in it. Another extraordinary thing about the lichens is that the new individual resulting from
this association differs considerably from either of the partners in form and habit. The fungi obtain food
either saprophytically from dead organic matter or parasitically from the living bodies of host organisms.
The fungal partner is also for protection against dessication, fog, excessive light intensity and fluctuations
of temperature. The alga prepares food material for both due to the presence of chlorophyll. This type of
association is called symbiotic relationship. In lichen, both of them are benefitted from the association
and neither can survive alone in the environment. Lichens thus are biotrophic in their mode of
nutrition as they obtain their food from the living algal associate. Probably food materials from the alga
diffuse out and are absorbed by the fungus. The reproductive organs, however, are entirely fungal in
character. Every individual of a given lichen species contains the same alga and the same fungus. This dual
nature of the lichen thallus has been confirmed experimentally. People have been successful in building up a
new lichen individual out of a fungus and its appropriate alga. The algal component in the association may
belong to the Cyanophyceae (blue green algae) or to the simple Chlorophyceae (green algae). It may be
filamentous or non-filamentous. In the majority of the lichens, the alga is unicellular. About 26 genera of
algae are involved. Of these, 8 are blue-green, 17 green algae and 1 yellow green. The common blue-
greens are Nostoc, Stigonema, Rivularia and Gloeocapsa and the most common green algae
are Protococccus, Trentepohlia, Cladophora, etc. About 80% of all lichen thalli contain green algae.
Nearly 20% of known fungal species are associated with lichens. The fungal components are usually
member of Ascomyctetes, sometimes Basidiomycetes and rarely Deuteromycetes. The study of lichens is
called Lichenology and a person who has specialized in the study of lichens is called a Lithenologist.
The Lichen thalli are generally of three kinds, crustose, foliose and fruticose. Internally the thallus
particularly in the foliose lichens consists of four regions namely, the upper cortex, the algal layer, the
medulla and the lower cortex. Asexual reproduction by asexual spores and sexual reproduction are entirely
the functions of the fungal partner. The carpogonium is a coiled, multicellular filament. It consists of a
coiled, multicellular ascogonium and a straight, multicellular trichogyne. There is a pore in the centre of
each septum between the cells of the trichogyne. The antheridia which are flask-shaped receptacles are sunk
in the upper surface of the thallus. Male cells or spermatia are non-motile. Each has a cell wall around it.
The ascus fruit in many species is of apothecium type and in others of perithecium type. The contents of
each ascus are fashioned into eight haploid ascospores. The ascospores may be simple or septate. Each
ascospore under suitable conditions germinates to produce fungal hyphae which if it comes in contact with a
proper alga, develops into a new lichen. If the fungal hypha fails to find an appropriate alga, it perishes.
Habit and Habitat
They are world-wide in distribution growing in diverse habitats. They are mostly confined to the tropics
and subtropics where there is plenty of moisture. They usually grow on tree trunks, walls, rocks, roofs of
houses, branches of trees, etc. They are usually xerophytic in nature and can withstand extremes of heat,
cold and drought. Some species are able to survive in such conditions where no other plants could survive.
They grow on high mountain elevation and in extreme cold alpine and arctic regions. Some aquatic species
occur only on the sea shore. The factors favouring lichen growth are direct light, moderate or cold
temperature, pure atmosphere, firm substratum and sufficient atmospheric moisture. The conditions unsuited
for the growth of lichens are scanty precipitation, hot and dry summer. Lichens often have a regular but very

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slow growth rate of less than a millimeter per year. According to their habitat, Lichenologists divide the
lichens into three categories, saxicolous, corticolous and terricolous.
Saxicolous: Lichen that grows on rock / stone is called a saxicolous lichen. E.g. Dermatocarpon,
Xanthora. They grow on firm substratum in cold regions. Lichens that grow on the rock are epilithic, and
those that grow immersed inside rock, growing between the crystals with only their fruiting bodies exposed
to the air, are called endolithic lichens.
Corticolous: A crustose lichen that grows on bark is called a corticolous lichen. E.g. Usnea, Graphis.
They are mostly confined to the tropics and subtropics where there is abundant moisture. Here they grow on
the leaves and bark of trees as epiphytes depending on their hosts for anchorage only. A lichen that grows on
wood from which the bark has been stripped is called a lignicolous lichen. Lichens that grow immersed
inside plant tissues are called endophloidic lichens or endophloidal lichens. Lichens that use leaves as
substrates, whether the leaf is still on the tree or on the ground, are called epiphyllous or folicolous.
Terricolous: A Lichen that grows on the soil as a substrate is terricolous. E.g. Collema, Cladonia. Many
squamulous lichens are terricolous. A squamulose lichen is a lichen that is composed of small, often
overlapping scales called squamules. If they are raised from the substrate and appear leafy, the lichen may
appear to be foliose lichen, but the underside does not have a skin (cortex), as foliose lichens do.
Umbillicate lichens are foliose lichens that are attached to the substrate at only one point e.g. Lasallia
papulosa. A vagrant lichen is not attached to substrate at all, and lives its life being blown around by wind.
Colouration
Lichens come in many colors. Coloration is usually determined by the photosynthetic component. Special
pigments, such as yellow usnic acid, give lichens a variety of colors, including reds, oranges, yellows, and
browns, especially in exposed, dry habitats. In the absence of special pigments, lichens are usually bright
green to olive gray when wet, gray or grayish-green to brown when dry. This is because moisture causes the
surface skin (cortex) to become more transparent, exposing the green photobiont layer. Color is used in
identification. The color of a lichen changes depending on whether the lichen is wet or dry. Color
descriptions used for identification are based on the color that shows when the lichen is dry. Dry lichens
with a cyanobacterium as the photosynthetic partner tend to be dark grey, brown, or black. The underside of
the leaf-like lobes of foliose lichens is a different color from the top side (dorsiventral), often brown or
black, sometimes white. A fruticose lichen may have flattened branches, appearing similar to a foliose
lichen, but the underside of a leaf-like structure on a fruticose lichen is the same color as the top side.
2. Lichen thallus
On the basis of their general habitat of growth, form and manner of attachment to the substratum,
usually three basic forms of lichens are recognized. They are:
1. Crustose lichen
It is a crust like, thin, flat hard layer of thallus. The thallus remains closely attached to the substratum by
its whole lower surface. The upper surface of the thallus bears a number of small cup-shaped fruiting
bodies, the apothecia containing asci and ascospores. E.g. Graphis, Lecanora, Lecidia, Rhizocarpon, etc.
2. Foliose lichen
The thallus is broad, many lobed, leaf-like which
remains loosely attached to the substratum
by rhizinae which act as an anchorage and
absorptive organs. The upper surface possesses
several fruiting bodies the apothecia. Apothecium is
formed only by fungal components. E.g. Physcia,
Parmelia, Peltigera, etc.
3. Fruticose lichen
It is the most common type of lichen where thallus
shows much branching. The tips of branches bear
fruiting bodies the apothecia. The thallus remains
attached to the substratum only at the base by a
flattened disc. The disc is composed of strands of
densely packed hyphae. Thallus may be erect or
Fig 1: Different forms of lichen thallus pendant. E.g. Evernia, Usnea, Cladonia, Ramalina.

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3. Classification of lichens
Many scientists classify the lichens on the basis of:
A. Nature of fungal elements- According to Miller (1984) lichens are divided into two classes:
i. Ascolichen: Lichen in which the fungal component is an Ascomycetes. It is subdivided into two groups
according to ascocarp.
a. Gymnocarpeae (Discolichen) in which ascocarp is apothecium type (disc shaped). E.g. Parmelia,
Xanthoria, Graphis, Lecanora, Usnea, etc.
b. Pyrenocarpeae (Pyrenolichen) in which ascocarp is perithecium type (flask shaped). E.g.
Dermatocarport, Pyrenula.
ii. Basidiolichen or Hymenolichen: Fungal component is a Basidiomycetes. eg. Corella, Rhipidonema.
B. Kind of fruitification (structure of asci and ascocarps)- According to Poelt (1973), Henssen and Jahns
(1974), Alexopolous ans Mims (1979) lichens are divided into three classes:
i. Ascolichens: Fungal partner is ascomycetes.
a. Hymeno-ascolichens: Unitunicate (single walled) asci in apothecia.
b. Loculo-ascolichens: Bitunicate (double walled) asci in apothecia or hysterothecia.
c. Loculo-ascolichens: Bitunicate (double walled) asci in pseudothecia.
ii. Basidiolichens: Fungal component is a Basidiomycetes.
iii. Deuterolichens (the lichens imperfecti): Fungal component is Deuteromycetes. Mostly sterile lichens
that produce no spores.
4. Structure of lichen thallus
The part of a lichen that is not involved in reproduction, the body or vegetative tissue of a lichen, is called
the thallus. The thallus form is very different from any form where the fungus or alga are growing
separately. The thallus is made up of filaments of the fungus called hyphae. The filaments grow by
branching then rejoining to create a mesh, which is called being anastomose. The mesh of fungal filaments
may be dense or loose. Generally, the fungal mesh surrounds the algal or cyanobacterial cells, often
enclosing them within complex fungal tissues that are unique to lichen associations.
Fruticose, foliose, crustose lichens generally have up to three different types of tissue forming
different layers. The top layer, where the lichen contacts the environment, is called a cortex. The cortex is
made of densely tightly woven, packed, and glued together fungal filaments. The dense packing makes the
cortex act like a protective skin, keeping other organisms out, and reducing the intensity of sunlight on the
layers below. The cortex may be further topped by an epicortex of secretions (not cells). This secretion layer
may or may not have pores. Below the cortex layer is a layer called the photobiontic or symbiont or algal
layer. The symbiont layer has less densely packed fungal filaments, with the photosynthetic partner (alga)
embedded in them. The less dense packing allows air circulation during photosynthesis. Each cell or group
of cells of the photobiont is usually individually wrapped by hyphae, and in some cases penetrated by
a haustorium. The layer beneath the symbiont layer is called the medulla. The medulla is less densely
packed with fungal filaments than the layers above. In foliose lichens, there is usually, as in Peltigera,
another densely packed layer of fungal filaments called the lower cortex.
Foliose lichens have upper cortex, algal layer in which algae are
diffused among the fungal filaments, medulla and lower cortex
which is densely packed layer of fungal filaments. Root-like
fungal structures called rhizines grow from the lower cortex to
attach or anchor the lichen to the substrate. Fruticose lichens
have a single cortex wrapping all the way around the stems and
branches, algal layer which is sharply distinct from the layer
below and medulla is the lowest layer which may form a cottony
white inner core for the branch like thallus, or it may be hollow.
Crustose lichens lack a lower cortex, and the medulla is in
Substrate direct contact with the substrate that the lichen grows on. Alga in
the algal layer is diffused among the fungal filaments.
Fig 2: Structure of lichen thallus

Types of lichen thallus

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i. Homoiomerous: Lichen thallus exhibits a simple structure with little differentiation. It consists of loosely
arranged fungal hyphae in which the algal cells are equally distributed throughout. E.g. Collema, Leptogium.
ii. Heteromerous: Most of the lichens belongs to this category. The
thallus belonging to this category shows considerable differentiation as
four zones like upper cortex, algal layer, medulla and lower cortex.
Algal component is confined to a specific region. E.g. Parmelia,
Peltigera.
Structure associated with the lichen thallus
Associated with lichen thallus are certain other vegetative structures
peculiar to lichens only. They are:
(i) Breathing pores: In certain species of lichens
particularly the foliose forms (Parmelia) the compact
nature of upper cortex is interrupted at intervals by some
opening called the breathing pores. The fungal hyphae are
loosely interwoven. The tissue beneath the breathing pore
is more of less medullary in nature. Breathing pores serve
for aeration and may be in level with the surface or raised
on cone-like elevations on the thallus.
(ii) Cyphellae: Aerating organs in the form of organised
breaks also occur in the lower cortex of a few foliose
forms (Sticta sylvatica). To the naked eye these appear as
small cup-like white spots. Under the microscope each
spot is seen as a roundish cavity or a concave circular depression where white medulla is exposed. Here the
hyphae grow directly from the medulla and abstrict empty rounded cells in a spore-like manner at their tips.
Such aerating or breathing pores in the lower cortex may or may not have a definite border formed by the
edge of the cortex. In the former case they are called the cyphellae and in the latter pseudocypheliae. They
help in aeration.
(iii) Cephalodia: These are small warty, hard, dark-coloured outgrowths on the upper surface of the thallus.
They contain fungal hyphae of the same type as the mother thallus, but the algal elements are always
different. For example, in Peltigera aphthosa the cephalodium contains a blue-green alga but the algal
component in the thallus is of a bright, green kind. They probably help in retaining the moisture.
(iv) Isidia: These are small outgrowths on the upper surface of the lichen thallus each consisting of an outer
cortical layer followed by an algal layer of the same kind as in the thallus. The isidia vary in form in
different lichen species. In Parmelia they are rod-shaped, coralloid in Umblicaria, cigar-shaped in Usnea
and scale-shaped in Collema. The chief function of isidia appears to increase the photosynthetic surface of
the lichen thallus and sometimes it acts as organ of vegetative reproduction (Fig. 4).

Fig 4:
Fig 3:

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5. Reproduction
A) Vegetative reproduction
a) By fragmentation: Death and decay of older parts of the thallus produce smaller pieces which give rise
to new thallus.
B) By propagules
(i) Soredia: It is the most common method of vegetative reproduction. Soridia are small protuberances (bud
like outgrowths) arised from the algal zone below the upper cortex
of 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. Soredia are
very light in weight and are easily disseminated by wind or rain
wash. After falling on suitable substratum, they develop into new
lichen (Fig. 5). E.g., Parmelia, Bryoria, etc.
(ii) Isidia: These are small outgrowths on the upper surface of the
lichen thallus each consisting of an outer cortical layer followed by
an algal layer of the same kind as in the thallus. The isidia vary in
form in different lichen species. In Parmelia they are rod-shaped,
coralloid in Umblicaria, cigar-shaped in Usnea and scale-shaped in
Fig 5: Collema. Isidia are usually constricted at the base and thus can be
easily broken off. Under the favourable condition each isidium
grows into new lichen thallus (Fig. 4).
Reproduction of fungal component (Mycobiont)
i) Asexual reproduction by sporulation: Certain lichens may also reproduce asexually by means of conidia
(e.g., Arthonia), oidia and Pycnidiospores (Fig. 6). However, it is of rare occurrence. In some cases hyphae
break down into small pieces known as oidia while 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 obstruct sexual
spores (pycnidiospores) at their tips. After falling on suitable substratum pycnidiospores germinate and
coming in contact with appropriate alga, they develop further into new lichen.
ii) Sexual reproduction (Oogamous type)
Only fungal partner of the lichen reproduces sexually and forms
fruit bodies on the thallus. The nature of sexual reproduction in
ascolichen is like that of the members of Ascomycotina, whereas
in Basidiolichen is like that of Basidiomycotina members. This is
because the lichen fungus produces either ascospores or
basidiospores. The male reproductive organ is called the
spermogonium (pycnidium) and the female is known as
carpogonium. The spermogonium mostly develops close to
carpogonium. They develop either on the same hypha or on two
different hyphae of the same mycelium.
a. Spermogonium (pycnidium): The spermogonia (pycnidia)
(Fig. 6) are flask shaped structures embedded in the upper Fig 6:
surface of the thallus. They open outside by a small pore known
as ostiole. The fertile hyphae lining in the inner cavity of the
spermogonium produces numerous non-motile minute rounded
cells at its tip which are male cells. They are known as spermatia
(male gamete). In some species of lichens, however, the pycnidia
like structures also function as spermogonia. The spermatia are
set free in a slimy mass which oozes out through the ostioles.
b. Carpogonium: A carpogonium is multicellular which
develops in the medulla of the young lobes of the thallus (Fig. 7).
It consists of two parts i.e. lower coiled multicellular portion Fig 7: Carpogonium
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called ascogonium and upper long, straight, thread like multi-cellular portion called trichogyne. Ascogonium
lies deep in the medullary portion while trichogyne emerges out of the thallus and receives spermatia.
Fertilization: The spermatium, after liberating from the spermogonium, gets attached with the trichogyne at
the sticky projected part. On dissolution of the common wall, the nucleus of spermatium migrates into the
carpogonium and fuses with the egg. After fertilization trichogyne withers. Many ascogenous hyphae
develop from the basal region of the fertilised ascogonium. The binucleate penultimate cell of the
ascogenous hyphae develops into an ascus. Both the nuclei of penultimate cell fuse and form diploid nucleus
(2n), which undergoes first meiotic and then mitotic division resulting in eight haploid daughter nuclei. Each
haploid nucleus with some cytoplasm metamorphoses into an ascospore. The asci remain intermingled with
some sterile hyphae, the paraphyses. With further development, asci and paraphyses become surrounded by
vegetative mycelium and form fruit body. The fruit body may be ascohymenial type i.e., either apothecium
(Fig. 8A) as in Parmelia and Anaptychia or perithecium as in Verrucaria and Darmatocarpon or ascolocular
type (absence of true hymenium), which is also known as pseudothecia or ascostroma.
Internally, the cup-like (Fig. 8B, C) grooved region of a mature apothecium consists of three distinct parts;
the middle thecium (hymenium), comprising of asci and paraphyses, is the fertile zone covered by two
sterile zones, the upper epitheca and lower hypotheca. The region below the cup is differentiated like the
vegetative thallus into outer cortex, algal zone and central medulla (Fig. 8B).
In ascolichen, usually the asci contain eight ascospores (Fig. 8C), but the number may be one in Lopadium,
two in Endocarpon and even more than eight in Acarospora. The ascospores may be simple or septate,
unicellular or multicellular, uninucleate or multinucleate, and are of various shapes and sizes. After
liberating from the ascus, the ascospore germinates in suitable medium and produces new hypha. The new
hypha, after coming in contact
with proper algal partner,
develops into a new thallus.
In Basidiolichen, the result of
sexual reproduction is the
formation of basidiospores that
developed on basidium as in
typical basidiomycotina. The
fungal member (belongs to
Thelephoraceae) along with
blue green alga, as algal partner
forms the thalloid plant body.
The thallus grown over soil
produces hypothallus without
rhizines, but on tree trunk it
grows like bracket fungi and
differentiates internally into
upper cortex, algal layer,
medulla and lower fertile
Fig 8: region with basidium bearing
6. Fruiting body basidiospores.
(A) Apothecium (apothecia): Structure of Apothecium
It is round and cup-shaped structure (Fig. 8A). If the apothecium consists only the fungal component, it is
known as lecideine type (e.g., Lecidea, Cladonia, Gyrophora) and if it consists bath algal and fungal
components it is known as lecanorine type (e.g., Lecanora, Parmelia). It can be divided into two parts:
(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. This layer is also
called hymenial layer or hymenium. Each ascus contains 8 ascospores (Fig. 8C). Ascospores are of various
shapes and size, multicellular, uni- or bitunicate and uni- or multinucleate. The sterile tissue that separates
the asci is called hamathecium. As many as four types of hamathecial tissues are identified in an ascocarp.
These are:

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i. Paraphyses: Arise from the base of ascocarp and grow upwards (Fig. 9A).
ii. Paraphysoides: They are formed by stretching of the tissues of ascocarp before the development of asci
(Fig. 9B).
iii. Periphysoides: Arise from the roof of ascoscarp and grow downwards (Fig. 9C).
iv. Periphyses: Arise in the ostiolar canal and
protrude outside the ostiole (Fig. 9D).
(b) Sub-hymenium: The region consists of the
closely interwoven sterile hyphae. It is present just
below the fertile layer.
(2) Margin of Apothecium
This part surrounds the disc and also forms the edge
Fig 9: of the apothecium.
(B) Perithecium (Perithecia): Structure of perithecium
Perithecia are a type of globose or flask-shaped fruiting bodies (ascocarp) containing the asci where the
hymenium is completely enclosed by protective sterile tissue, except for a small opening at the tip, the
ostiole (Fig. 10). At maturity the ostiole allows release of the ascospores. Perithecia are usually partially
embedded in the thallus and appear as a small dot on the surface. Lichens in which the fruiting body is a
perithecium are termed pyrenocarpous.
The hymenium, the tissue containing the asci, is
seated at the base of the perithecial cavity. Tissues
penetrating between the asci, collectively
the hamathecium, may consist of:
 Paraphyses: Septate, usually unbranched filaments,
developing and extending upwards from
the hypothecium, the tissue below the hymenium;
 Pseudoparaphyses: Septate filaments, often
branched and anastomosed, initiating from the roof
of the perithecial cavity and extending downwards
into the hymenium;
 Paraphysoids: Other tissue within the perithecium,
becoming stretched into branched and anastomosed,
slender filaments as the perithecium develops and
Fig 10: Structure of perithecia generally with septa remote and inconspicuous.
E.g. Pyrenula microspora, P. nitida
7. Importance of Lichens
A. Economic Importance of Lichens
The lichens are useful as well as harmful to mankind. The useful activities are much more than harmful
ones. They are useful to mankind in various ways: as food and fodder, as medicine and industrial uses of
various kinds.
1. As Food and Fodder: Lichens are used as food by human being in many parts of the world and also by
different animals like snail, catterpiliars, slugs, termites etc. They contain polysaccharide (lichenin),
cellulose, vitamin and certain enzymes. Some species of Parmelia are used as curry powder in India,
Endocarpon miniatum is used as vegetable in Japan, Evernia prunastri for making bread in Egypt, and
Cetraria islandica (Iceland moss) as food in Iceland. Others like species of Umbillicaria, Parmelia and
Leanora are used as food in different parts of the world. In France, some of the lichens are used in the
preparation of chocolates and pastries. Lichens like Lecanora saxicola and Aspicilia calcarea are used as
food by snails, caterpillars, termites, slugs etc. Ramalina traxinea, R. fastigiata, Evernia prunastri, Lobaria
pulmonaria are used as fodder for animals, due to the presence of lichenin, a polysaccharide. Animals of
Tundra region, especially reindeer and muskox use Cladonia rangifera (reindeer moss) as their common
food. Dried lichens are fed to horses and other animals. In India, Everniastrum cirrhatum is used as holy
material for sacrificial fire in ceremonies and also being used as spice and flavoring agent for vegetables and
meats. Lethariella cashmeriana, L. sernanderi, L. sinensis, Thamnolia vermicularis and T. subuliformis are
used to prepare tea in the Yunnan Province of China.
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2. As Medicine: Lichens are medicinally important due to the presence of lichenin and some bitter or
astringent substances. The lichens are being used as medicine since pre-Christian time. They have been used
in the treatment of jaundice, diarrhoea, fevers, epilepsy, hydrophobia and skin diseases.
Cetraria islandica and Lobaria pulmonaria are used for tuberculosis and other lung diseases; Parmelia
sexatilis for epilepsy; Parmelia perlata for dyspepsia; Cladonia pyxidata for whooping cough; Xanthoria
parietina for jaundice and several species of Pertusaria, Cladonia and Cetraria islandica for the treatment
of intermittent fever. Usnic acid, a broad spectrum antibiotic obtained from species of Usnea and Cladonia,
are used against various bacterial diseases. Usnea and Evernia furfuracea have been used as astringents in
haemorrhages. Some lichens are used as important ingredients of many antiseptic creams, because of having
spasmolytic and tumour-inhibiting properties. H. diademata in India among the Nepalese living in Gangtok
(Sikkim) is used for cuts and to heal wounds.
3. Industrial Uses: Lichens of various types are used in different kinds of industries.
(i) Tanning Industry: Lichens like Lobaria pulmonaria and Cetraria islandica are used in tanning leather.
(ii) Brewery and Distillation: Lichens like Lobaria pulmonaria are used in brewing of beer. In Russia and
Sweden, Usnea florida, Cladonia rangiferina and Ramalina fraxinea are used in production of alcohol due
to rich content of lichenin, a carbohydrate.
(iii) Preparation of Dye: Dyes obtained from some lichens have been used since pre- Christian times for
colouring fabrics etc. Dyes may be of different colours like brown, red, purple, blue etc. The brown dye
obtained from Parmelia omphalodes is used for dyeing of wool and silk fabrics. The red and purple dyes are
available in Ochrolechia androgyna and O. tartaria. The blue dye Orchil, obtained from Cetraria islandica
and others, is used for dyeing woollen goods. Orcein, the active principal content of orchil-dye, is used
extensively in laboratory during histological studies and for dyeing coir. Litmus, an acid-base indicator dye,
is extracted from Roccella tinctoria, R. montagnei and also from Lasallia pustulata.
(iv) Cosmetics and Perfumery: The aromatic compounds available in lichen thallus are extracted and used
in the preparation of cosmetic articles and perfumes. Essential oils extracted from species of Ramalina and
Evernia are used in the manufacture of cosmetic soap. Ramalina calicaris is used to whiten hair of wigs.
Species of Usnea have the capacity of retaining scent and are commercially utilised in perfumery. Evernia
prunastri and Pseudevernia furfuracea are used widely in perfumes. Similar use of lichens in India to
prepare incense powder was also reported without giving species and incense ingredients details. It was
estimated that about 7,800 to 9,200 t lichens are collected to manufacture perfume in Morocco, Yugoslavia
and France.
Harmful Activities of Lichens
i. Some lichens like Amphiloma and Cladonia parasitise on mosses and cause total destruction of moss
colonies.
ii. Lichen like Usnea, with its holdfast hyphae, can penetrate deep into the cortex or deeper, and destroy the
middle lamella and inner content of the cell causing total destruction.
iii. Different lichens, mainly crustose type, cause serious damage to window glasses and marble stones of
old buildings.
iv. Lichen like Letharia vulpina (wolf moss) has Vulpinic acid which is highly poisonous.
v. Lichens may be the source of fire in forest.
B. Ecological Importance of Lichens
Lichens have some ecological importance.
1. Pioneer of Rock Vegetation (role in succession): Lichens are typically the first organisms to colonize
bare rock. They are therefore the pioneer species in primary succession. Many organisms require soil before
they can colonize an area. But, due to their ability to grow with minimum nutrients and water, the crustose
lichens colonise the bare rock with luxuriant growth. The lichens secrete some acids which disintegrate the
rocks and start the soil formation process. After the death of the lichen, it mixes with the rock particles and
forms thin layer of soil. The soil provides the plants like mosses to grow on it as the first successor, but,
later, vascular plants begin to grow in the soil. In plant succession, Lecanora saxicola, a lichen, grows first;
then the moss Crtmmia pulvinata, after its death, forms a compact cushion on which Poa compressor grows
later. As Poa die, the soil thickens more allowing other hardy species to colonize. The process continues
until a mature forest forms, sometimes centuries later.
2. Accumulation of Radioactive Substance: Lichens are efficient for absorption of different substances.
The Cladonia rangiferina, the reindeer moss, and Cetraria islandica, the Iceland moss are the commonly
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available lichens in Tundra region. The fallout of radioactive strontium (90Sr) and caesium (137CS) from the
atomic research centres are absorbed by lichen. Thus, lichen can purify the atmosphere from radioactive
substances. The lichens are eaten by caribou and reindeer and pass on into the food chain, especially to the
Lapps and Eskimos. Thus, the radioactive substances are accumulated by the human beings.
3. Sensitivity to Air Pollutants (bio-indicator of air pollution): Bio-indicators are living organisms that
respond in an especially clear way to a change in the environment. The hardy lichens are useful bio-
indicators for air pollution, especially sulphur-dioxide (SO2) pollution, since they derive their water and
essential nutrients mainly from the atmosphere rather than from the soil. It also helps that they are able to
react to air pollutants all year round. Compared with most physical/chemical monitors, they are inexpensive
to use in evaluating air pollution. Lichens can also be used to measure toxic elemental pollutants and
radioactive metals because they bind these substances in their fungal threads where they concentrate them
over time. Environmental scientists can then evaluate this accumulation to determine the history of the local
air. Lichens are injured by SO2. Not all lichens are equally sensitive to air pollutants, so different lichen
species show different levels of sensitivity to specific atmospheric pollutants. The most sensitive lichens are
shrubby and leafy while the most tolerant lichens are all crusty in appearance. The sensitivity of a lichen to
air pollution is directly related to the energy needs of the mycobiont, so that the stronger the dependency of
the mycobiont on the photobiont, the more sensitive the lichen is to air pollution. Upon exposure to air
pollution, the photobiont may use metabolic energy for repair of its cellular structures that would otherwise
be used for maintenance of its photosynthetic activity, therefore leaving less metabolic energy available for
the mycobiont. The alteration of the balance between the photobiont and mycobiont can lead to the
breakdown of the symbiotic association. Therefore, lichen decline may result not only from the
accumulation of toxic substances, but also from altered nutrient supplies that favor one symbiont over the
other. This interaction between lichens and air pollution has been used as a means of monitoring air quality
since 1859, with more systematic methods developed by William Nylander in 1866.
Since industrialisation many of the shrubby and leafy lichens such as Ramalina,
Usnea and Lobaria species have very limited ranges, often being confined to the parts of Britain with the
purest air such as northern and western Scotland and Devon and Cornwall. Rose (1975) has calculated that
more than one-third of England and Wales has lost nearly all its epiphytic lichens (lichens that grow on tree
trunks and branches), the most delicate shrubby lichens, largely due to the SO2 emissions of coal-burning
power plants. In Northern Siberia, an area of the Soviet Union which is very polluted, the number of lichen
species has fallen from 50 to about 3, and the lichen production in general stands at about 1 or 2% or normal
levels, threatening the reindeer diet; in Alaska there are similar concerns about lichen reduction and the
caribou diet (Tyson, 1990). Losses in other parts of the world reflect the increasingly poor quality of the
earth's air and the need for early warning bio-indicators such as lichens. This pollutant has natural sources,
such as volcanic eruptions and sea spray. By far the largest source for it, however, is the combustion of
fossil fuels, automobile emissions, and some industrial processes. The pollutant is carried in the atmosphere
until rained out or deposited as dry particles or as gas. Sulphur-dioxide combines with moisture in the
atmosphere to form sulphurous acid (H2SO3) or sulphuric acid (H2SO4). When this happens with rainwater,
the result is acid rain. All these forms of sulphur are harmful to lichens and plants. Lichens have also shown
sensitivity to some other pollutants, such as heavy metals and ozone, but for the most part lichen damage can
be attributed to SO2. The effect of pollution upon lichen depends on the pH of the substrate, the surface on
which the lichen grows. In general, an alkaline substrate such as basic bark or limestone counteracts the
acidity of SO2 pollution. As acid rain falls on a substrate, one kind of lichen growth form will often be
replaced by another more tolerant form. In areas of high pollution lichens may be found only on sites such as
wounds on trees and on sandstone walls, which have high pH. In some areas, although gaseous sulphur
dioxide levels have fallen, the bark of older trees is too acidic for recolonisation, and new growth develops
on twigs and younger trees. Some species of lichens have become more widely distributed than they were a
century ago as they are more tolerant of acid conditions, such as some species of Bryoria, Parmeliopsis,
Pseudevernia and Rinodina.
4. Lichenometry: Lichenometry is a technique used to determine the age of exposed rock surfaces based on
the size of lichen thalli. Introduced by Beschel in the 1950s, the technique has found many applications. It is
used in archaeology, palaeontology, and geomorphology. It uses the presumed regular but slow rate of
lichen growth to determine the age of exposed rock. Measuring the diameter (or other size measurement) of
the largest lichen of a species on a rock surface indicates the length of time since the rock surface was first
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exposed. Lichenometry is especially useful for dating surfaces less than 500 years old, as radiocarbon
dating techniques are less accurate over this period. The lichens most commonly used for lichenometry are
those of the genera Rhizocarpon (e.g. the species Rhizocarpon geographicum) and Xanthoria.
8. Distribution of lichens in Nepal
More recent literature survey reveals 792 species of lichens belonging to 187 genera (Olley and Sharma,
2013). Ten percent of the Nepalese Lichens are endemic to Nepal (n=55). There were 172 species reported
from above the treeline (4300 m) and 29 of these were endemics. Carbonea vorticosa in Nepal Himalaya at
7400 m was the world’s highest reported lichen. Their highest richness of lichens was observed between
3100–3400 m and endemic species in between 4000–4100 m. Almost 33% of the total lichens and 53% of
the endemic species occurred above the treeline (> 4300 m). Non-endemic richness had the same response
as the total richness. All growth forms showed a unimodal relationship of richness (Baniya et al., 2010).
9. Economic importance of lichens with reference to Nepal
Lichens are being used in traditional foods and medicines since millenia and also play vital roles in
ecosystem function and human welfare. During the mid eighteenth century, regular crops were badly
affected in Europe by frosts and droughts causing famine, and as a consequence, lichens were used for food
because of their easy availability, cheapness and nutritive value. Most of the lichens are non-poisonous
although some exceptions exist. Letharia vulpina, Cetraria pinastri, Bryoria fremontii and B. tortuosa are
well known poisonous lichens contain vulpinic acid or pinastrinic acid. A total of 792 species belonging to
187 genera of lichen-forming fungi have been reported from Nepal. Study by Devkota et al. (2017) revealed
six uses of lichens by the residents of Taplejung, Gorkha and Solukhumbu. Medicinal value, ritual and
spiritual value, food value, aesthetic and decorative value, bedding value and ethno-veterinary value are the
major uses of lichens. Heterodermia diademata and Ramalina species were used for medicinal values,
Everniastrum cirrhatum, E. nepalense, and Parmotrema cetratum for food value, Usnea longissima for the
ritual, spiritual, aesthetic values and as bedding materials, and Thamnolia vermicularis for the aesthetic and
spiritual values. Heterodermia diademata is used to treat wounds and to stop bleeding after an injury.
Extracts or juices of Artemisia vulgaris or Eupatorium odoratum mixed with this lichen species are used to
cure fresh wounds or cuts. Ramalina sp. is used as antiseptic tincture to heal wounds. Although lichens
occur from outer Tarai to the high mountains, the use of lichens in cuisine is observed only among Limbu,
Rai and partly with Sherpa and Tamang ethnic groups. These groups are major dwellers of Eastern midhills
and mountainous regions of Nepal. Major dishes prepared with steamed lichens are pickle, curry, soup and
sausages. Everniastrum nepalense, E. cirrhatum and Parmotrema cetratum is used to prepare meal dishes.
Freshly harvested or purchased lichens (about 250 g) are boiled for about 1 h with ash (about 50 g), rinsed in
clean cold water until any yellow color is gone, sun dried on bamboo woven baskets and placed in closed
containers in a dry place. Boiled and dried lichens can be stored for a year. For bread making, boiled, dried
and powdered lichens are mixed mainly with wheat or barely flour (1:3 mixed lichens and flour). Limbu
people prepare a special traditional dish called Sargyangma made of lichens to celebrate their special
gatherings and social functions like Dashain, Tihar and in some cases, when a pig is slaughtered in the
community. Everniastrum cirrhatum, E. nepalense and Parmotrema cetratum were much preferred species
and found to be sold in local weekly markets in the district headquarter of Taplejung. Study found that since
the last 5–7 years, the demand for edible lichens is rising, especially from abroad. Thousands of Rai and
Limbu families from Eastern part of Nepal are living abroad (mainly in UK and Hongkong) and they want to
taste lichen during their festivals. Lichens are also considered as the best gift item in such communities.
Heterodermia diademata together with Eupatorium odoratum for the treatment of fresh wound and cuts was
reported among Limbu community of eastern Nepal. In traditional herbal therapeutic practice in Far-western
Nepal, lichen extract and decoction were applied to treat moles. Thamnolia vermicularis is also used as
antiseptic in Western Himalayas to kill buttermilk borne worms. Uses of T. vermicularis among
mountainous Sherpa community are more common than in the midhills communities. Usnea sp. are used as
bedding materials and stuffing materials for the pillow and alternatively as mattresses at seasonal camps
(Devkota et al. 2017).
Ritual, spiritual and aesthetic values
Study by Devkota et al. (2017) revealed that Thamnolia vermicularis was used on the belief that this lichen
wards off evil spirit and maintains peace at home and among family members so handful of this lichens was
kept above the main entrance of a house. Six villages of Taplejung district inhibiting the Rai, Limbu, Sherpa

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used this lichen. Such practice was common among the Buddhist and Kirant cultural groups. Similarly,
people of Olangchung Gola and Ghunsa used Usnea longissima to clean religious cups like butter lamps
(Diyo in Nepali) and water bowls made of silver. With wet U. longissima, pots are scrubbed to remove
stains. Usnea longissima and Thamnolia vermicularis were used as ingredients in incense powder mainly by
the Sherpa and Lama ethnic groups, residing in Olangchung Gola, Ghunsa and Tsum valleys. They mixed
these dried lichens with dried leaves of Juniperus indica, J. squamata, Rhododendron anthopogon, R.
decorum, R. lepidotum and roots of Jurinea dolomiaea. They burn incense powder during their morning
pray and religious ceremonies which releases pleasant and fragrant smoke. Usnea longissima was used for
decoration that was being practiced among the Sherpa community of Olangchung Gola settlement of
Kangchenjunga Conservation Area. The lichen was collected fresh and either framed making different
shapes (designs) or simply hangs around in a room and for the decoration in a corner of reception desks by
hotelier at Olangchung Gola, Khumjung and Namche, Solukhumbu district.
Lichens and animal husbandry
Heterodermia diademata is used as an antiseptic and healing agents against external injuries in cattle
(Sheep) in Chekampar, Gorkha District. Usnea longissima is used as bedding materials for colt, chick,
newly born goats and yak calves mainly by herders in Solukhumbu, Gorkha and Taplejung. Interestingly, it
was not used as bedding materials for human and rarely used as stuffing material for pillow, for reasons
being unknown. Kiraat religious group (Limbu and Rai) used three lichen species (Everniastrum nepalense,
E. cirrhatum, Parmotrema cetratum) mainly for their food value while the Buddhism religious group
preferred lichens (Heterodermia diademata, Usnea longissima, and Thamnolia vermicularis) for medicinal
and ritual and spiritual values. Only a low number of Hindu (Brahman and Chhetri) uses lichens (Bhattarai
et al. 2000; Limbu and Rai 2012; Devkota et al. 2017).
The lichens collected in West Nepal are mainly used in international trade, while those in East Nepal
are used locally for food. A total of 20 commercially important species of lichens were identified from five
trade centres and one local market. During 2000–2011, Nepal legally exported 2020 tons of lichens and
collected NRs 25,293,305 (USD 240,000). The average annual quantity of turnover was 168 tons, though it
is estimated that much was exported illegally. The hill districts in Nepal, which traded 1774 tons, were more
important for the collection of commercial lichen species than the Mountainous and inner-Tarai districts,
which traded 167 and 108 tons, respectively. Through the Forest Act, Forest Regulations and its amendment
in 2011, the collection of lichens for harvest, trade and export in any crude or processed form was banned.
However, the legislation lacks an effective implementation strategy, and sustainable harvest of lichen
resources based on scientific data would better serve local livelihood and lichen conservation in Nepal.
Screening the lichens has revealed the frequent occurrence of metabolites with antibiotics, anti-
mycobacterial, antiviral, anti-inflammatory, analgesic, antipyretic, anti-proliferative and cytotoxic
properties. Even though these manifold activities of lichen metabolites have now been recognized, their
therapeutic potential has not yet been fully explored and thus remains pharmaceutically unexploited (Muller,
2002).

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