Truffle is the common name given to the fruit bodies produced by mushrooms belonging to the Tuber species, whose entire life cycle occurs underground.
These special mushrooms colonise the roots of trees or shrubs establishing a close-knit relationship called mycorrhizal symbiosis.
Mycorrhizal fungi coat the tree roots with threads, penetrating the initial levels of root cells.
The relationship between the two is very close and, in some extreme environments; several plant species can only survive thanks to the mycorrhizae.