2. Lichens
■ Lichenology
■ Defined as structurally organised entity consisting of the permanent
association of a fungus and an algae.
■ Predominant partner Mycobiont and Sub-ordinate partner
Phycobiont.
■ Symbiosis
■ This true nature of lichens was first identified by Simon
Schwendener.
3. Occurance and Habitat
■ Lichens are world wide in distribution.
■ They include about 500 genera and 1800 species growing from polar regions to the
equator on a very wide variety of habitats
■ They can tolerate the extreme dessication and grow in the direct sunlight or remain
buried in snow for long periods without any injury
■ The most usual habitats of lichens are tree barks, decaying woods, leaves, branches,
undisturbed soul rich in humus, sand, stones and rocks Lichens which grow on stones
are called saxcoles and those growing on barks of trees are called cortcoles and those
growing on soil are called as Terricolous.
■ A few species of lichens are aquatic.
■ In India, they occur in Himalayas and other higher hills of South India at an altitude
ranging from 4,000 to 10,000 ft.
■ Lichens are highly pigmented and have various colours. They may be bluish green, grey,
yellow, orange, reddish or brownish in colour due to pigmentation in algal partners.
4. COMPOSITION OF PLANT BODY
■ Each lichen plant consists of two components-a fungus (mycobiont) and an alga
(phycobiont).
■ The fungal component of lichens either belong to Ascomycotina or
Basidiomycotina. The algal components of lichens usually belong
1. Cyanophyta- 08 genera of cyanophyceae viz, Nostoc, Scytonema, Rivularia, and
2. Chlorophyta- 18 genera of chlorophyceae viz., Coccamyxa, Myrmela,
Trebouria,Cladophora,Pleurococcus
3. Xanthophyta- One genus
4. Phaeophyta- One genus
■ Hole (1967) divided lichens into 3 classes on the basis of their fungal components
1. Ascolichens , 2 .Basidiolichens and 3. Lichens imperfecti
5. EXTERNAL FORMS OF LICHENS
■ The lichens vary in their size and shape. The smallest lichen measures about 1 mm
in diameter. They are classfied into 3 different forms on the basis of the type of
thalli and mode of their occurrence
1. Crustose (or Crustaceous) lichens: Examples- Graphix, Lecanona ,Rhizocarpon, etc.
2. Foliose (or Foliaceus) lichens: Examples- Peligera, Parmelia, Gyrophora etc.
3. Fructicose (or Filamentous) lichens: Examples- Cladonia, Ramalina, Evernia etc.
6. Internal Structure of Lichens
1. The mycobiont constitutes the major
part of the lichen body and
only 5% part is made up of
phycobiont.
2. The body is divided into the upper
cortex, algal zone (gonidial layer),
middle medulla, lower cortex and
rhizines.
3. Only the algal zone contains
photosynthetic partners.
4. In about 98% of lichens, the fungal
partner belongs to Ascomycetes. In
the rest, the fungal partner belongs to
Basidiomycetes and Deuteromycetes.
9. Economic Importance of Lichens
Some of the important uses of lichens are as follows:
1. Pioneers of rock vegetation
2. Soil farmers
3. Orchin dye is obtained from Roccella tinctoria.
4. Litmus is obtained from Rochella montagnei.
5. Cladonia rangiferina (Reindeer moss) is an edible and good source of antibiotics.
6. Ramalina, Evernia are used in perfume industries.
7. Lichens are air-pollution indicators. They do not grow where there is specifically SO2
pollution.
8. Many lichens are useful in producing medicines, for e.g., Usnea and Cladonia.
9. They are used in tanning leather, for e.g., Lobaria pulmonaria.
10. Some lichens like Usnea are used in the brewing industry.
