A lichen is made up two or more organisms, which form a symbiotic relationship with each other for survival. These organisms include a fungus and an alga or sometimes a cynobacteria. Some lichens can consist of all the three organisms at once.
1 Additional Answer
A lichen is made of fungus and algae. These two form a relationship, whereby they exchange essential substances such as food and water. Lichens can survive in very extreme environments such as over rocks and on the mountain peaks.