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In this article we will discuss about:- 1. Meaning of Lichen 2. Types of Lichens 3. Reproduction 4. Economic Importance.
Meaning of Lichen:
Lichens (Fig. 200) constitute an extraordinary group of mostly grayish-green plants widely distributed all over the world. They grow on rocks, tree-trunks, dead wood and on ground, and can withstand extreme temperature. A lichen is a peculiar combination of an alga and a fungus, the two live deriving mutual benefit.
Major part of a lichen is usually composed of fungal hyphae enclosing some algal cells irregularly or in a definite layer. Alga manufactures carbohydrate food- which becomes available to the fungus, and the fungus, in return, absorbs and retains water and thus keeps the algal cells moist.
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That makes life of lichens possible in very dry situations where individually none of them can thrive. Thus lichen is an excellent example of symbiosis or reciprocal parasitism.
Types of Lichens:
According to forms, lichens are of three principal types, viz.:
(i) Crustose forms, which grow on rocks and barks as incrustations,
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(ii) Foliose forms, with flat leaf-like thalli, and
(iii) Fruticose forms, which hang from trees or grow erect on the ground.
Reproduction of Lichen:
Lichens multiply vegetatively when small fragments break away from the parent plant and carried by different agencies. Each piece can produce a new thallus. Often special reproductive bodies, called soredia, are formed as bud-like outgrowths on the thallus.
A soredium consists of a few algal cells surrounded by fungal hyphae. They get detached from the plant, are carried away by wind and give rise to new thalli. Lichens also reproduce by spores called pycnidiospores. The spores germinate to produce fungal hyphae which develop into lichen after coming in contact with a suitable alga.
Economic Importance of Lichen:
Lichens growing in extremely cold regions serve as main food for animals like reindeers. Some of them contain pigments. Common litmus used as an indicator of acidity and alkalinity, is extracted from lichen. A few of them are also used in perfume industry. Lichens bring about disintegration of rocks on which they grow, and thus prepare suitable ground for growth of other plants.
