How is a lichen different from a plant or animal?

A lichen is not a single organism; it is a stable symbiotic association between a fungus and algae and/or cyan bacteria.

Symbiotic means any two life form that can only exist with the two life forms are together. There are many examples of this in the plant world, where a plant only have one pollinator and the pollinator only feeds on that plant.

Like all fungi, lichen fungi require carbon as a food source; this is provided by their symbiotic algae and/or cyan bacteria, that are photosynthetic.

The lichen symbiOSis is thought to be a mutualism, since both the fungi and the photosynthetic partners, called photobionts, benefit.