They get bad press for being poisonous, but are not as bad they are made out, just don’t eat them! They are one of the most obvious mushrooms to identify, and difficult to confuse with anything else.
These fungi are found under trees, because they form a very close relationship with tree roots known as a mycorrhizal association. This relationship allows trees to take up nutrients that they would not normally be able to reach, and the fungus is given a share of the bounty in return. It is a mutually beneficial relationship, and vitally important to the health of the trees, who, without their fungal partners, will not thrive.
Fungi are not plants, they are more closely related to animals, even though they may look plant like. This structure is just the fruiting body, the main body of the fungus is underground and consists of a very fine network of threads which cover huge areas. In fact one fungus in America has been estimated to have an underground network that covers 3 square miles, is about 2000 years old, weighs about 600 metric tonnes- and is the largest organism known on the planet!