Q.2. Write a short account of lichens and add a note on their uses. (BSc 1st Year Botany Lichens)
Ans.2.
ECONOMIC IMPORTANCE OF LICHENS
- Formation of Soil or Ecological Importance: Initiation of vegetation on the rocks and soil formation. Lichens, especially the crustose lichens, are of considerable ecological importance as pioneers in the colonisation of rocky habitats by the plants. The acids produced by these lichens bring about the disintegration and erosion of rock surface. The minerals so released are utilised by the lichen which get established on the barren rock. When these lichens die, their decaying remains mix with the rock particles to form fertile soil in which other plant are able to grow.
- Biochemical weathering and pedogenesis: The crustose lichens affect the chemistry of the rocks on which they grow by producing a series of activities. These activities are collectively called “biological weathering’. The activities are mainly because of the secretion of some soluble organic acids by the mycobiont. The main organic acid is oxalic acid, which causes surface etching and ultimately disintegrates the rocks over which the lichens are growing (Syers and Iskander, 1973).
This surface etching by oxalic acid first produces honeycomb-like structure on the rocks, and then disintegration of rocks into finer particles of soil. The process of the formation of this new soil is called ‘pedogenesis’. Dead organic remains of the thalli mix with these fine particles of the new soil, which ultimately becomes fertile enough for other plants to grow.
- Bioindicators of air pollution: Lichens, especially the epiphytic lichens, are particularly useful as bioindicators of air pollution. These are extremely sensitive to air pollution, and the SO2 in the atmosphere is particularly inhibitory to lichens. Exposure to SO2 reduces the efficiency of the photosynthetic activity by the phycobiont, allowing the mycobiont to overgrow it and leading to the elimination of the symbiotic relationship. Once, the delicate metabolic balance is interrupted, the lichen and its fungal and algal components disappear from the habitat. So, the lichens can provide quick, easy and inexpensive information about the extent of air pollution in a given area. For example, by examining lichens on trees, it is possible to determine the extent of air pollution and even the direction of the source of air pollutants.
- Food Value: Several lichens are consumed as food for insect and their larva. Some lichens such as Cladonia rangiferina a commonly called as Reindera grass and is an food by reindeers arctics. Some lichens such as Certraria icelandica, Umbillc asila, Lecanora, etc. used as food by human beings. In madras a species of Parmelia known in Telgu as rethapu or rock flower has been used in carry preparation and is famous for its delicacy.
- Medical Value: A lichen commonly known as Iceland “moss” produce mucilagenous substance which is used as laxative. It is also ingredient of slaves, pudding and cultural media for bacteria. Several more lichens produces some medicines.
- Drugs from lichens: Some lichens are useful as drugs, as shown by the following examples:
- Usnic acids, produced from many lichens, have antibiotic properties, and are effective against many Gram-positive bacteria.
- Many antiseptic creams, such as ‘Usno’ and ‘Evosin’ are available in the market, and well-known for their tumour-inhibiting, spasmolytic and virucidal properties.
- Erythrin, obtained from Roccella montagnei, is used in angian, a serious heart disease.
- Some lichens have protolichesterinic acid, a compound used in the preparation of some anti-cancer drugs.
- Some lichen compounds (lichenin and isolichenin) have anti-tumour properties.
- Use of Lobaria pulmonaria and Cetaria islandica in tuberculosis and other lung diseases is known since very early times.
- Some lichens are used with tobacco because of their hallucinogenic effects.
As source of dyes: Many lichens produce dyes which have been in use for centuries for colouring fabrics and paints. These include orchil, a beautiful blue dye; and cudbear another blue dye. Orchil, obtained from the lichen Roccella, was used for dyeing woollen and silk fabrics. Orcein, a purified extract of orchil is used as a stain in the laboratories for microscopic observations.
Lichens also serve as a source of litmus commonly used as an indication of acidity in the laboratory. Litmus solution is made by grinding the lichen, Roccella tinctoria and extracting the colouring matter, after which the paper is soaked in the neutralized solution. This solution is used to prepare litmus paper.
- Perfumes from lichens: Pseudewernia furfuraceu and Evernia prunastri are widely used in the manufacture of perfumes. The remainder, left after the preparation of perfumes from lichens, contains compounds such as naphthalene, camphor, geraniol and borneol.
- Uses in Tanning, brewing and distilling: The astringent substances extracted from the thalli of Cetraria islandica and Lobaria pulmonaria have been in use for tanning leather. Lobaria pulmonaria has also been used in the brewing of beer. Cladonia rangiferina and certain species of Usnea and Ramalina have been used in the preparation of alcohol.
- For religious purposes: Lichens are used in the preparation of perfumes for manufacturing dhoop and havan samagries which are used for performing religious ceremonies.
Harmful aspects
(A) Lichens are, quite often, responsible for forest fires. During hot months, dry lichens on tree trunks catch fire quickly, which is transmitted to the tree tops. The thalli of Usnea are particularly inflammable.
(B) Lichens of the genera Cladonia and Amphiloma cause total destruction to the colonies of mosses by direct parasitic attack
(C) Lichens often get attached to the window glasses in old buildings and errode them with the help of acids released by them.
(D) Poison from lichens: Letharia vulpina (volf moos) is used as a poison for wolves when mixed with powdered glass. Vulpine acid, present in this lichen, is responsible for its poisonous nature.
BSc 1st Year Botany Lichens Sample Model Practice Question Answer Papers