Essay On Lichen

Review of literature:

Lichen Symbiosis

Lichens are composite organisms with leading symbiotic association with fungus and algae/cyanobacteria or both in addition to chemolithotrophic bacteria (Nash 1998 and Bates et al 2011). Although, Lichens are useful to monitor air quality and indicate atmospheric trace element pollutions, numerous investigations strongly evidenced that interface between lichen and rock substrates leading to weathering of minerals and can be accelerated by the growth lichen species. The effects of lichens on their mineral substrate include the both physical and chemical process which may include mechanical disruption of rock caused by hyphal penetration, expansion and contraction of lichen thallus, swelling action of organic and inorganic salts release. While chemical weathering by the

They grow just few millimeter or centimeter in a year. Lichens can grow in diverse climatic conditions and on various substrates. The lichens growing on bark or tree trunk are called as corticolous, on twigs as ramicolous, on dead wood - legnicolous, on rocks and boulders - saxicolous, on moss - muscicolous, on soil - terricolous and on evergreen leaves – foliicolous (Figure 2 – 8). The lichens can grow under water rocks, but not purely in water or ice. The lichens are widely distributed in almost all the phytogeographical regions of the world. Adequate moisture, light and altitude, unpolluted air and undisturbed substratum often favours luxuriant growth of lichens.

By their appearance the lichens can be grouped into three main growth forms,

Crustose lichens: The lichen thallus is closely attached to the substratum without leaving any free margin. The thallus usually lacks lower cortex and rhizinae (root like structure). Such lichens have to be collected along with their substratum for the study (Figure 2). Fig 2: Crustose lichens harboured on rock surface at Chitradurga fort