Gymnopilus aeruginosus is a species of mushroom belonging to the family Hymenogastraceae. It is known for its distinctive blue-green (aeruginous) coloration, which gives it its name. This species is part of the Gymnopilus genus, which includes several mushrooms with varying degrees of psychoactivity, although the psychoactive properties of Gymnopilus aeruginosus are not well-documented.

Gymnopilus aeruginosus typically grows on decaying wood, particularly on stumps, logs, and buried wood of hardwood trees. It is found in temperate regions, primarily in North America, and typically fruits in the fall.

Morphologically, Gymnopilus aeruginosus has a cap that ranges from greenish to blue-green when young, often fading to yellowish or brown as it ages. The cap is convex, becoming more plane with age, and can have a scaly surface. The gills are attached to the stem and vary from yellow to orange-brown as the spores mature. The stem is typically similar in color to the cap and may bruise blue-green, a trait that adds to its distinctive appearance.

This species is sometimes confused with other psychoactive Gymnopilus species, though reports of its psychoactivity are limited and inconsistent. Gymnopilus aeruginosus is more often studied for its ecological role in wood decomposition rather than its psychoactive properties. As with all wild mushrooms, proper identification is crucial, as some species in the Gymnopilus genus can be toxic.