A tree fungus infects a tree by entering it through a wound or weak spot and producing growths such as mushrooms or shelf-like structures called conks. These fungal structures can appear on the limbs, trunk or root system. Long, root-like structures called rhizomorphs sometimes appear along the base of a tree. While some types of fungus are edible, such as certain mushrooms, these parasitic plants can cause branch die-off. Severe infections can kill trees.
Armillaria is an example of a mushroom fungus. It takes hold around the base of a tree, producing clusters of honey-colored mushrooms with caps 1.5 to 6 inches wide. All of the spores are located on the underside of the caps. They disperse when ready, creating even larger clusters of mushrooms. This fungus also has dark brown rhizomorphs, which cling to the roots or under the bark of hardwoods; this is a secondary reproduction strategy.
Ganoderma lucidum and ganoderma applanatum are examples of fungi that form shelf-like structures. Long, flat structures often form along the tree base, spreading out as they grow. Both types of fungus are brown to reddish-brown with a white edge, though applanatum tends to be lighter. The shelf-like structures reach from 8 to 14 inches across. The spores form on the underside of the shelves and turn brown when mature.