G. applanatum is known as a conk, which is a general term for a fungus that destroys wood. It is a called a white rot fungus due to its ability to digest the brown lignin in a tree as food source and leave behind the white cellulose.
G. applanatum, appropriately dubbed a shelf fungus due to the shape, is a fan-shaped polypore that can range from 30-70 cm long, making it very noticeable in the woods. It has a thick, hard, lumpy, brown top with several radiating zones. The spore surface is ochre in color, unless scratched off in which case the spore surface becomes brown. The pores of the spore surface are tiny and regular in shape.
Each year, G. applanatum creates a new pore surface, giving it a “stacked” appearance.
Its common name is the artist’s conk because of the pictures one can draw when the white pore surface is scratched to reveal a brown color.
See Tom Volk’s page on Ganoderma applanatum