Mycorrhizas, or "fungus root" are fungi that live in a close symbiotic relationship called mutualism, with trees found in the forest. As the trees carry out photosynthesis, some of the carbon is given to the fungi. Fungi, on the other hand provide additional nutrients for the trees and help them get more water than their own root system can accomplish. Fungi are able to extend the root system of the plant, enabling the plant to gain access to more water and nutrients than would be possible alone. Another relationship is between trees and moss or algae. Sometimes, moss or algae grow on the side of a tree, which is benefical because they can receive more light than would be available on the forest floor amongst the leaf litter. It is an example of commensalism because the tree is neither harmed nor helped by this relationship.
One example of symbiosis is the caterpillars of the Large Blue butterfly with the species of red ants known as Myrmica sabulet. The caterpillars feed on flowers initially but when they grow large they give off a pheromone which makes the ants allow them to enter and live in the ant’s nest where the caterpillar eats ant grubs. The ants in return get a sugary substance that the larva excretes from a special honey gland it has.
Lichen is another example of a symbiotic relation. Lichen is actually made of a fungus and an alga. The fungus here provides a solid structure for the alga to live in and the alga produces the energy for the lichen through photosynthesis.