A close-up of a tree trunk with various types of lichen growing on it. The trunk is light grey and has a rough texture. The lichen is green, yellow, and white, and it grows in patches and splatters across the bark.
Lichen is a symbiotic organism that is made up of a fungus and an alga or cyanobacterium. It grows on rocks, trees, and other surfaces and can survive in harsh conditions. The different colours of lichen in the image are likely due to different species of lichen being present.
