General account of Lichen Dr. Rajeev Kumar Guest Assistant Professor Department of Botany Bihar National College, Patna (Patna University) General features of Lichen • The branch of biology which deals with the study of Lichen is called Lichenology. • Lichens are considered to be a group of thallophyta although made up of two different groups i.e. algae and fungi. • Lichens are distributed worldwide and comprising about 400 genera and 13500 species. • Lichen found in India in Himalayan region and hills of south India. • Lichen are highly pigmented and have various colors like green, yellowish, bluish, orange, reddish etc. • The color of Lichen is due to presence of pigment found in algal partner. General features of Lichen • The algal part of Lichen is called phycobiont and the fungal part is called mycobiont. • The algal partner is usually a member of Chlorophyta or Cyanophyta where as the fungal partner belongs to Ascomycetes or Basiomycetes. • The algal partner produced carbohydrate by the process of photosynthesis that is utilized by both of them and the fungal partner serves the function of absorption and retention of water. • In Lichens, the algal partner and fungal partner is associated and show mutual relationship so that it is an example of symbiosis. General features of Lichen • The fungal partner protect algal partner from unfavorable conditions and provides shelter and in turn algal partner provides food to fungi. • In this association the fungi get more benefits than algae so that this type of partnership is called Helotism that means unequal partnership. • Lichen are called Bioindicators because lichen are very sensitive to pollution particularly air pollution. • Lichen do not grow in the highly polluted regions like metro cities and industrial area. • The growth of Lichen is very slow. Composition of Plant body • The phycobiont may belongs to generally Chlorophyceae, Cyanophyceae and rarely belongs to Xanthophyceae, Phaeophyceae. • The mycobiont may belongs to generally Asccomycetes Basidiomycetes and rarely Deuteomycetes. Types of Lichens On the basis of occurrence Lichens can be divided into four types – 1. Corticoles – Lichens growing on bark of trees. 2. Saxicoles - Lichens growing on stones. 3. Terricoles- Lichens growing on soil surface. 4. Follicoles- Lichens growing on leaves. Types of Lichens On the basis of morphology Lichens can be divided into following types – 1. Crustose Lichen 2. Leprose Lichen 3. Foliose Lichen 4. Fruticose Lichen Crustose Lichen- • The thallus is of insignificant size. It is flat, thin usually without any distinct lobes. It is just like a thin layer or crust closely attached by the whole of its lower surface to stones or rocks, bark and similar hard substratum. They are partially or wholly embedded on substratum. e.g. Graphis, Lecidia etc. Leprose lichen – It is the simplest type of Lichen in which lichen appears as powdery mass on the substratum called leprose. e.g. Lepraria Foliose Lichen – • The foliose thallus is flat, broad, much lobed and leaf-like. It often resembles crinkled and twisted leaves. It grows more or less free of the substratum but close to it. It has a distinct upper and a lower surface. The lower surface may be white or sooty. Some part of the thallus are attached with the substratum by means of hyphal outgrowth called rhizines. e.g. Peltigera, Parmelia etc. Fruticose Lichen • They are shruby lichen where thalli are well developed found as cylindrical, branched and shrub like structure. The thallus shows no differentiation into upper and lower surfaces. e.g. Cladonia , Usnea etc. Classification of Lichen Alexopoulos and Mims(1979) classified Lichen into three main groups – 1. Ascolichen – The fungal partner belongs to Ascomycetes. e.g. Parmelia, Cetraria 2. Basidiolichen –The fungal partner belongs to Basidiomycetes. e.g. Dictyonema. 3. Deuterolichen – The fungal partner belongs to Deuteromycetes. Reproduction in Lichen Lichen reproduces by all the three means that is – 1. Vegetative reproduction 2. Asexual reproduction 3. Sexual reproduction Vegetative Reproduction in Lichen Fragmentation – It takes place by accidental injury where the thallus of Lichen broken into fragments and each part is capable of growing into a new thallus. By death of older parts – The basal part of thallus of Lichen dies and after that some lobes or branches like structure are separated from thallus and each lobes or branches grows into a new thallus. Asexual Reproduction in Lichen • By Soredium – Soredium are small greyish white bud like outgrowth developed on the upper cortex of thallus. They are detached from the thallus by wind or rain and on germination grow into a new thallus. • By Isidium- Isidium are small stalked or branched greyish black coral like outgrowth developed on the upper surface of thallus. Under favorable condition the isidium germinates and gives rise to a new thallus. Sexual Reproduction in Lichen • Only fungal partner of lichen reproduces sexually and form fruit bodies on the thallus. • In Ascolichen, the male sex organ is called spermogonium and the female sex organ is called carpogonium.The carpogonium is multicellular and differentiated into basal ascogonium and trichogyne. The spermogonium liberates spermatium and gets attached with trichogyne The nucleus of spermatium migrats in carpogonium and fuses with egg. Sexual Reproduction continue….. • Many ascogenous hyphae develop from the basal region of fertilized ascogonium. The binucleate ascogenous hyphae develop into ascus. Both the nuclei fuses and after first meiotic and then mitotic division eight daughter haploid nuclei formed. • Each haploid nuclei with some cytoplasm metamorphoses into an ascospores. Economic importance of Lichen • Lichens are called pioneer species for rock vegetation. • Lichen acid causes weathering of rock into soil particles. • Lichens are bioindicators so they acts as indicators of air pollution. • The antibiotic Usnic acid is obtained from Usnea. • Cladonia are used by animals as food. • Litmus is obtained from lichen e.g. Rocella montegni. • Lecanora is used by human as food. • Peltigera canina and Lobaria pulmonaria have medicinal value. References • Gupta SK, 1992.New Botany Vol. I, Kedarnath Ramnath & Co, Meerut • Gangulee and Kar,1994. College Botany Vol. II, New central Book Agency, Kolkata.