Mycena is a large genus of small saprotrophic mushrooms that are rarely more than a few centimeters in width. The name Mycena comes from the Ancient Greek μύκης mykes, meaning "fungus". Species in the genus Mycena are commonly known as bonnets.

Mycena haematopus, commonly known as the bleeding fairy helmet, the burgundydrop bonnet, or the bleeding Mycena, is a species of fungus in the family Mycenaceae, of the order Agaricales. It is widespread and common in Europe and North America, and has also been collected in old Japan and Venezuela. It is saprotrophic—meaning that it obtains nutrients by consuming decomposing organic matter—and the fruit bodies appear in small groups or clusters on the decaying logs, trunks, and stumps of deciduous trees, particularly beech. The fungus, first described scientifically in 1799, is classified in the section Lactipedes of the genus Mycena, along with other species that produce a milky or colored latex.