what is lichen class 11 biology

Lichens are a small group of plants of composite nature, consisting of two dissimilar organisms, an alga and a fungus living in a symbiotic association. The fungal partner is composed of filamentous cells, where every filament is called a hypha. The most common fungi in lichens are species of Ascomycetes or Basidiomycetes. The green algae Chlorophyta or Cyanophyceae family of blue-green bacteria are the most common algal partners. Lichens exist in different growth forms, including crustose, foliose, squamulose, and fruticose. They are found worldwide and can colonize a wide range of surfaces, including tree bark, exposed rock, and as a part of biological soil crust. Lichens have been used by humans as food and as sources of medicine and dye.