Lichen is thallophytic, composite and symbiotic organism. Lichen is an association of algae and fungi. The fungi member is known as mycobiont and algae member is known as phycobiont. About 15000 species are included in this group.
Lichens are very good example of symbiosis where algae being autotrophic manufactures the food through photosynthesis and the fungi absorbs water and minerals from the substratum, as well as fungi provide rigidity to the thallus.
Lichens are placed in fungi group according to five kingdom classification .
Lichens are grayish green or greenish, white, yellow, orange, brown, red and black in colour. Lichens can be observed on the old wall, rocks, stems and branches or shrubs and trees, logs of wood and on ground. Some of the lichens are very resistant and may survive for long periods of desiccation. Lichens are able to invade the bare rocks and make the environment suitable for other forms of life also. Lichens play an important role in xerophytic plant succession.
External structure and classification of Lichens
If the fungal member belongs to the class ascomyctes the lichen is classified as ascolichens and if fungal member belongs to bsidiomycetes the lichen is classified as basidiolichens. The lichens are of three types:
Reproduction in Lichens
Lichens reproduce by following three methods:
Vegetative reproduction : Vegetative reproduction is a process in which new offspring produces through the body of single organism. The different types of vegetative reproduction takes place in lichens are by soredia, isidia and cephalodia.
Asexual reproduction :
Asexual reproduction takes place by the formation of spores formed by the fungal partner. Each spore on germination sends hyphae in all directions and spore comes in contact with the requisite alga, spore branches and covers up the algal cell. This combined body forms a lichen thallus. In many lichens, a flask shaped cavity called pycnidium is formed, from where spore like pycnidiospores develop and when they come in contact with the requisite alga, they form new thallus.
Sexual reproduction takes place in certain ascolichens. The fruiting body is either a cup shaped apothecium or a flask shaped perithecium. Sex organs are well differentiated, the male is flask shaped chamber called spermogonium, within numerous, minute, non motile cellsa are formed. Female organ is called as carpogonium. Carpogonium consists of basal swollen portion called the ascogonium, and a upper tubular portion called the trichogyne. The male and female sex organs on maturation undergo the process of fusion. As a result of the fertilization and further growth the final product, i.e. the fruiting body is formed.
Useful activities of Lichens
The uses of Lichens are given below:
Harmful activities of Lichens
Some harmful activities of lichen are as given below:
So, dear friends, these are some important detail of Lichens. You can find this lichen at natural places and lichen is a good species to preserve in herbarium .
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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