Lichens

Lichens are a distinct group of plants produced by the intimate association of two organisms, a fungus and an alga. The two organisms live in such close association with each other that they appear to be a single organism.

The two partners

• The fungus taking part in the formation of a lichen is called the mycobiont.
• The algal component is called the phycobiont. The phycobiont synthesizes organic food for itself and for the fungus.

There are about 500 genera and 90,000 species of lichens (Wilson, 1992). They grow on the walls and roofs of houses, on leaves, on tree bark, on dead wood, or even in soil. Generally they are xerophytic in nature. The plant body is a thallus and is grey-green, orange, red, brown or black in colour. The thallus is irregular in shape.