Panellus stipticus, commonly known as the bitter oyster, the astringent panus, the luminescent panellus, or the stiptic fungus, is a species of fungus in the family Mycenaceae, and the type species of the genus Panellus. Used traditionally as a styptic to staunch bleeding, and also as a violent purgative

The luminescence is localized to the edges of the gills and the junction of the gills with the stem and cap. Bioluminescence is also observable with mycelia grown in laboratory culture, and the growth conditions for optimal light production have been studied in detail. Several chemicals have been isolated and characterized that are believed to be responsible for light production. Genetic analysis has shown that luminescence is controlled by a single dominant allele. The luminescent glow of this and other fungi inspired the term foxfire, coined by early settlers in eastern and southern North America. Modern research has probed the potential of P. stipticus as a tool in bioremediation, because of its ability to detoxify various environmental pollutants.