Gymnopilus underwoodii is a species of agaric fungus in the family Hymenogastraceae.

Originally described in 1896 by Charles Peck as Flammula underwoodii, the fungus was given its current name by William Murrill in 1917.

[2] The specific epithet honors American mycologist Lucien Underwood.

[3] Gymnopilus underwoodii has been found on pine logs and trunks.

It is found in the US, from Virginia to Alabama and in Florida, fruiting from November to December.