lichen1.ppt

this ppt is about lichens (symbiotic organisms)

1. Lichens

2. Lichen
•An association of a fungus and a photosynthetic
symbiont resulting in a stable vegetative body
having a specific structure
•Unique entity formed by a fungus and a
photoautotroph (alga or cyanobacterium)
•Widely distributed –grow on soil, rocks, trees,
marine or intertidal
•Variety of habitats –cold to hot, arid to moist
•Withstand environmental extremes

3. Lichens
•Are primary colonizers
in succession
•Involved in weathering
of rock and formation of
soil
•May exist where other
organisms can’t –
surface of desert rocks,
alpine, arctic, etc.

4. Air pollution
•Even though lichens are very resistant to
natural environmental extremes –they are
extremely sensitive to air pollution –
particularly SO
2
•Obtain nutrients from atmosphere, not soil

5. Fungal symbiont
•Most lichenized fungi are
Ascomycota –most form
apothecia, some form perithecia
and pseudothecia
•Some are Basidiomycota –
Aphyllophorales, few Agaricales
•Some are Deuteromycota

6. Characteristics of Lichens:
1.Lichens are a group of plants of composite thalloidnature, formed by the association of
algae and fungi.
2.2. The algal partner-produced carbohydrate through photosynthesis is utilisedby both
of them and the fungal partner serves the function of absorption and retention of
water.
3. Based on the morphological structure of thalli, they are of three types crustose, foliose
and fruticose.
4. Lichen reproduces by all the three means –vegetative, asexual, and sexual.
(a) Vegetative reproduction: It takes place by fragmentation, decaying of older parts, by
sorediaand isidia.
(b) Asexual reproduction: By the formation of oidia.
(c) Sexual reproduction: By the formation of ascosporesor basidiospores. Only fungal
component is involved in sexual reproduction.
5. Ascosporesare produced in Ascolichen.
(a) The male sex organ is flask-shaped spermogonium, produces unicellular spermatia.
(b) The female sex organ is carpogonium(ascogonium), differentiates into basal coiled
oogoniumand elongated trichogyne.
(c) The fruit body may be apothecia! (discshaped) or perithecial(flask-shaped) type.
(d) Ascidevelop inside the fruit body containing 8 ascospores. After liberating from the
fruit body, the ascosporesgerminate and, in contact with suitable algae, they form new
lichen.
6. Basidiosporesare produced in Basidiolichen, generally look like bracket fungi and
basidiosporesare produced towards the lower side of the fruit body.
7. The growth of lichen is very slow, they can survive in adverse conditions with high
temperature and dry condition.

7. Lichens are divided into following categories on the basis of their habitat:
1.Saxicolous.Grow on stones or rocks e.g., Dermatocarpon, Xanthoria, Verrucaria, etc.
2.Corticolous.Grow on bark of trees e.g., Grpahis, Usnea, Parmelia etc.
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3.Terricolous.Grow on soil (terrestrial) e.g., Cladonia florekeana, Lecidea, Collema etc.
4.Lignicolous.Grow directly on wood e.g., Calicicum etc.
5.Marine.Grow on siliceous rocky shores of sea e.g., Caloplaca, Verrucaria etc.
6.Freshwater.Grow on hard siliceous rocks in freshwater e.g„Epheba, Hymenelia etc.
Lichens are divided into following 3 sub-classes on the basis of their fungal partner
(A)Ascolichens.Fungus belongs to Ascomycetes.
It is further divided into two series depending on the fruiting body:
1. Gymnocarpeae.Fruiting body is an apothecium i.e., in the form of a more or less open disc, e.g.,
Parmelia.
2. Pyrenocarpeae.Fruting body is perithecium i.e., a closed structure e.g., Dermatocarpon.
(B)Basidiolichens.Fungus belongs to Basidiomycetes. There are only 3 genera which belong to
Basidiolichens. These are: Cora, Corella, Dictyonema

8. C.Hymenolichens.Fungus belongs to Deuteromycetes lichens are also known as
imperfect lichens.
On the basis of growth forms, and nature of attachment to the substratum
lichens are divided into following three types:
1.Crustose lichens (encrusting lichens).
These lichens occur as thin or thick crust over rocks, soil or tree barks. It is very
difficult to separate them from substratum. The thalli may be wholly or partially
embedded so that only fruiting bodies are visible above the surface of the
substratum e.g., Lecanora, Graphis, Rhizocarpon, Ochrolechia etc.

9. 2.Foliose lichens (leafy lichens).
These lichens are variously lobed, leafy structures attached to the substratum by
rhizoid like outgrowth called the rhizines e.g., Xanthoria, Parmelia, Physcia,
Anaptychia etc.
3.Fruticose lichens (Shrubby lichens).
These are the upright or hanging lichens (pendant forms) attached only at the base
by a flat disc. These are cylindrical, flat or ribbon like, well branched and resemble
with little shrubs e.g., Cladonia, Usnea, Alectoria etc.

10. 4. Squamulose-tightly clustered and slightly flattened pebble-like units. In
squamulose lichens, the thallus is composed of usually small, flat, usually
massed, often overlapping scales –‘squamules’. 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 eg Cladonia subcervicornis
Cladonia subcervicornis
5. Leprose Lichen:t has some fungal hyphae surrounding one or more algal
cells. A distinct fungal layer envelops the algal cells all over. It appears as a
powdery mass over the substratum e.g., Leparia incana

11. Usnea subfloridanaUsnea subfloridana
Crustose-crustlike, growing tight against the substrate.
Squamulose-tightly clustered and slightly flattened pebble-like units.
Foliose-leaflike, with flat sheets of tissue not tightly bound.
Fruticose-free-standing branching tubes.

12. Isidia

13. USES OF LICHENS
•Food
•Dyes (litmus paper, Harris tweed)
•Essential oils for perfumes, soaps
•Bioactive compounds (antiviral,
antibacterial)
•Nesting/bedding material
•Poisons

14. 1)LICHENS CONTRIBUTE TO SOIL FORMATION .
Lichens thrive in undisturbed sites where nothing else will grow. They grow on
rocks, barren soil and the bark of dead or live trees. They enrich the soil by
trapping water, dust and silt. When lichens die they contribute organic matter
to the soil, improving the soil so that other plants can grow there.
2)LICHENS FIX NITROGEN
Due to their association with algae, lichens are able to convert nitrogen in the
air into nitrates, (because they need for their growth). This nitrogen fixed by
lichens impacts the ecosystem,.. because when it rains, nitrates are leached
from lichens for use by nearby soil-based plants.
3)ECOLOGICAL IMPORTANCE:
Many Crustose lichens growing on rocks dissolve and disintegrate them into
soil particles.Limestone rocks are dissolved by the action of certain chemicals,
secreted by the lichens .When lichens die and decay, they form humus soil
together with rock particles, mosses, ferns and other plants grow on it. Thus
they prepare ground for succession of vegetation.
4.)Food for man and animals:
In Iceland Cetraria islandica commonly known as “Iceland moss” is grounded
up and mixed with wheat flour.

15. In Tamil Nadu a species of Parmelia known in Telugu as “rathapu” or rock
flower has been used in curry preparation and is famous for its delicacy.
The lichens serve as important source of food for invertebrates. A large
number of animals for example, mites, caterpillars, termites, snails, slugs etc.
feed partly or completely on lichens. Lichens as food have also been used by
man during famines. They are rich in polysaccharides, certain enzymes and
some vitamins.
5)Medicinal importance:
Peltigera canina, the dog lichen was used as medicine for hydrophobia in
ancient days and Lobaria pulmonaria, lungwort was used for the diseases of
lungs.
Since very early times the lichens are used to cure jaundice, fever, diarrhoea,
epilepsy, hydrophobia and various skin diseases. Various lichens are of great
medicinal

17. 7.) Habitat for Other Organisms
Lichens provide important habitat for many other organisms.They are an
excellent home for insects, arthropods, and other small invertebrates.Lichens
are also used by organisms to help build and insulate their homes.Birds, for
example, use various species of lichens (especially the fruticose types) to build
their nests.
8) A Source of Nitrogen
Nitrogen is a nutrient that is essential for living things.However, not many
organisms can add new nitrogen to an ecosystem.Many types of lichens are
able to capture nitrogen from the atmosphere and then secrete it into the soil
where it can be used by plants and passed on to other organisms.
9)Role in environmental pollution:
Lichens are very sensitive to atmospheric pollutants such as sulphur dioxide.
They are unable to grow in towns, cities and around industrial sites such as oil
refineries and brickworks. So, the lichens can be used as reliable biological
indicators of pollution. By studying lichens on trees, a qualitative scale has been
devised for the estimation of mean SO
2level in a given season. Thus lichens
are used as pollution monitors.

18. 10.)Chemical uses:
The lungwort lichen was also used in tanning, in perfumery and as a substitute
for hops in brewing. The cell walls of the fungi of certain lichens contain
colouring matters. Species of Rocella and Lecanorayield a most important
colouring matter known as Orchil or Cudbear. This is used in colouring
woollen and silk fabrics.
In Industry:
(i) Tanning and dyeing:
Some lichens are used in leather industry. Cetraria islandica and Lobaria
pulmortariashow the astringent property. This astringent substance is
extracted from the thallus and is used in tannin industry. Lichens are also used
in preparing natural dyes. Orchil, a blue dye obtained from Roccellaand
Leconara,is used to dye woollen articles and silk fabrics.
It is purified as orcum and used as a a biological stain. A brown dye is
obtained from Parmelia spp. whereas Ochrolechia spp. yield a red dye. Litmus
used as a acid-base indicator, is also a dye and is obtained from Roccella
tinctoria and Lasallia pustulata.

19. (ii) Cosmetics and perfumes:
Evernia, Ramalina, Pseudorina are reported to have perfumed volatile oils. Due
to the aromatic substances present in the thallus, the lichens are used in the
preparation of various cosmetic articles, perfumery goods, dhoop, hawan
samagris etc.
(iii) Brewing and distillation:
Some species of lichen for example, Cetraria islandica contain carbohydrates in
the form of lichenin. In Sweden and Russia alcohol is produced from these
lichens. These lichens are also used in confectionary.
(iv) Minerals:
Lecanora esculentais found in lime stone deserts and yields large amount of
calcium oxalate crystals. These are 60% of its dry weight.
Poison from Lichens:
Some lichens are poisonous due to presence of various substances in
them:

21. B. Harmful Aspects:
(a) Lichens growing on young fruit trees and sandal trees are
harmful to the plant.
(b) During hot season some species of lichens (e.g., Usnea
barbarata) become so dry and inflammable that they often help
in spreading forest fire.
(c) Some lichens act as allergens.
(d) The commercial value of glass and marble stone is reduced
because of itching of their surface by lichens.