This is a mushroom known as an “Artist’s Conk.” The fungus is aptly named for the way in which the white underside can be used as a medium for sketching, seen below.
While the top of the fungus is hard and woody, the underside is rather soft and covered in a white coating. Etching any sharp object such as a stick or pencil into this undersurface removes the white coating to expose the brown woody inside of the mushroom.
This species is referred to as a “bracket fungus” meaning it grows like a shelf on the side of hardwood and conifer trees. This means that sometimes it can be difficult to etch into the underside of these fungi being that the sketching surface faces the ground. Although we don’t recommend altering the state of nature, some artists prefer to remove the conks from trees to use as a sketching surface at home (be sure to check local/park rules before collecting!). After carving, artist’s commonly allow the shelf fungi to dry out with the pore surface facing up. The results are long-lasting.
Unlike most fungi, this unique mushroom grows year-round, in North and South America, Asia, Europe, and Australia, and can expand in size for well over a decade. To test the age of a bracket, one can break the organism in half, and – just as one would date a tree – count the number of concentric rings to indicate the years of growth.