3. INTRODUCTION
• An association of a fungus and a photosynthetic symbiont
resulting in a stable vegetative body having a specific
structure.
• Mycobiont – the fungal partner in a lichen.
• Photobiont – the photosynthetic partner in a
lichen; either a green 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
4. • One of the most successful
mutualistic associations in the world.
• Over 13,500 species based on the
mycobiont.
• Are primary colonizers in
succession
• Involved in weathering of rock and
formation of soil
• Worldwide distribution, often in the
most extreme environments, Arctic,
Antarctic, deserts and all other
habitats.
• Rare in polluted areas - intolerant of
industrial pollutants, especially
sulfur dioxide.
5. Fungal symbiont
• Most lichenized fungi are
Ascomycota – most form
apothecia, some form perithecia
and pseudothecia
• 12 orders include mostly
lichenized members
• Some are Basidiomycota –
Aphyllophorales, few Agaricales
• Some are Deuteromycota
6. Autotrophic symbionts
• Green algae – Trebouxia is a
common genus, found in
75% of lichens in temperate
zone
• Cyanobacteria – Nostoc is a
common genus
• 26 genera of algae and
cyanobacteria found in lichens,
90% of lichens contain
Trebouxia & Nostoc
7. Thallus morphology
4 basic types
• Fruticose - branched, strap shaped or threadlike
thallus, upright or hanging
• Foliose - flattened branching lobes loosely
attached to substratum, leaflike
• Crustose - flattened, scalelike
• Squamulose – intermediate
between foliose and crustose
9. Reproduction
• Sexual reproduction – characteristic of fungal
symbiont
• Ascospores are discharged, algal cells are not
discharged with them
• Thought that after ascospores germinate, they make
contact with algal cells
• Asexual reproduction – variety of
mechanisms – e.g. fragmentation
10. Asexual reproduction
• Specialized structures
• Soredia - algal cells
enveloped by hyphae,
no cortex, form
powdery masses on
surface of thallus,
detach from thallus
• Isidia – column like
structures with cortex
11. Growth
• Exhibit low growth rates – many grow at rates of
1-4 mm/yr, up to 9 cm/yr
• Makes studies difficult
Factors affecting growth
• Light – variable – some prefer low light
intensities, others high
• Temperature – variable
• Moisture – appears to be an important variable,
do not have water absorbing organs, depend on
moisture in air
12. Symbiotic association
• Fungus appears to be chief
benefactor, receives
– Organic compounds as C and
energy source
– With cyanobacteria, N
fixation may occur so that
the fungus also receives N
source
– Fungus produces substances
that absorb water which is
provided to alga
14. Assource of food
• Cetraria islandica was used as food
in Northern Europe and was cooked
as porridge, soup, bread, salad and
pudding.
• Bryoria fremoontii were mostly
used as food in times of famine in
North America so they were called
famine food.
• In China, lichens are used as food
(Lobaria isidiophra) and also as
health promoting tea (Thamnolia
subuliformis).
15. As fodder
1. Cladonia rangiferina in tundra
2. Cetraria islandica in iceland
3. Nutritive value is due to lichenin
Some lichens known as Earth Flowers have a
strong and distinct odour so they are
smoked along with tobacco used in
summer dances
17. Perfumes & dyes
• The extracts are used to dye wool.
• Xanthoria – yellow pigment
• They are also used in the manufacture of ‘moss’ and ‘leather’ &
fragrances in perfumes and some type of soaps
• Oakmoss - perfume
18. Lichensare advantage
over vascular plants
Asa bioindicator of air
pollution: because they
have no wax &cuticle to
protect cells(inner
structure)
Cortex:
Fungal layer
Algal layer
Medulla
19. References
• “What is a lichen?” Australia National Botanic garden . 10
october 2014
• “Lichen” Oxford Living Dictionary
• “Lichen Reproductive Structures” Ramel, Gordon
• “Lichenometry” Progress in Physical Geography
