· Term lichen was given by Theophrastus. · Composite dual organisms. · Symbiotic association between algae and fungi. · Pioneer colonizers of barren rocks and mountains. · The fungal partner absorb water and minerals from the substratum and algae prepare necessary food for both in · The algal component lichen usually belongs to Cyanophyceae (Nostoc, Scytonema). While fungal members usually belong to Ascomycetes and Basidiomycetes. · Many of the species of lichens can grow under extreme conditions of humidity and temperature. A. Habitat · Corticolous – growing on the bark of the tree. · Saxicolous – growing on rocky substrata or stone. · Terricolous – growing on the ground · Lignicolos – developing on wood eg. cyphelium · Marine – developing inshore of the sea. B. Types · Based on the general habit of growth form and manner of attachment to the substratum they are divided into A. Crustose lichen – Forms a thin crust closely adhered to the substratum, partly or...