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General characters of Lichens Posted on : 24-11-2017
Posted by : Admin
Lichens are a small group of curious plants of composite nature made up of two different organisms, an alga (phycobiont: in Latin phycos-alga; bios-life) and a fungus (mycobiont: in Greek mycos-fungus; bios-life). Algal and fungal components live in a truly intimate symbiotic relationship. This true nature of lichens was first identified by Simon Schwendener. He named the algal component as Phycobiont and the fungal component as Mycobiont.
General characters of Lichens
In general, the major portion of the thallus is occupied by the fungal component. The fungal component produces its own reproductive structures.
The algal partner makes the food by the process of photosynthesis. The food diffuses out and is absorbed by the fungal partner.
Owing to their symbiotic relationship, lichens can live in variety of habitats and climatic conditions including extreme environments.
Based on the substrate of growing, the lichens can be of following types
Corticolous (grows on tree barks),
Follicolous (grows on leaves surfaces),
Saxicolous (grows on rock surfaces),
Terricolous (grows on soil)
Musicolous (grows on mosses)
Lichen growth forms are generally visible on surfaces forming grayish, greenish or orange areas. They are classified mainly based on their morphology and size into three major types namely,
Crustose (crust like)
Foliose (leaf like)
Crustose lichens are called microlichens whereas foliose and fruticose lichens are called as macrolichens.
The main plant body of the lichen is called as thallus. Thallus is the vegetative portion and is similar to the vegetative portions of mosses and liverworts.
Mycobiont (Ascomycete or Basidiomycete) establishes an intimate symbiotic relationship with phycobiont (green algae or blue green algae). After association, both phycobiont and mycobiont lose tsheir uniqueness and they are known as lichens. Now the lichens act as a single organism, both morphologically and physiologically.
The method of reproduction in lichens is completely different from that of fungi and algae. Vegetative reproduction in lichens is through the development of special propagules called as diaspores. The most common diaspores of lichens are soredia and isidia.
The fungal partner of the lichens reproduces sexually. Sexual reproduction in the lichens is initiated by the production of fruiting bodies followed by formation of spores called as ascospores. Ascospores are resting spores which have the ability to tolerate adverse conditions.