Goldenedge bonnet

The cap of M. aurantiomarginata ranges in shape from obtusely conic to bell-shaped, and becomes flat in maturity, reaching diameters of 0.8–2.0 cm (3⁄8–3⁄4 in). The cap color is variable, ranging from dark olive fuscous (dark brownish-gray) to yellowish-olive in the center, while the margin is orangish. Alexander H. Smith, in his 1947 monograph of North American Mycena species, stated that the caps are not hygrophanous (changing color depending on the level of hydration), while Mycena specialist Arne Aronsen says they are. The overall color fades as the mushroom ages. The surface is moist, and young individuals are covered with fine whitish powder, but this soon sloughs off to leave a polished surface that develops radial grooves in maturity. The flesh is thin (about 1 mm thick in the center of the cap) and flexible. Gills are adnate with a decurrent tooth (where the gills curve up to join the stipe but then, close to the stipe, the margin turns down again), and initially narrow but broaden when old. They are pallid to grayish-olive with bright orange edges. Smith noted that the edge color may spread to the gill faces in some specimens, because the pigment, rather than being encrusted on the walls of the cystidia, is found in the cytosol and therefore more readily diffusible. …

Mycena aurantiomarginata is a saprobic fungus, deriving nutrients from decomposing organic matter found on the forest floor, such as needle carpets. Fruit bodies of the fungus grow scattered, in groups, or in tufts under conifers (usually spruce and fir), and are often found on moss. In North America, it is found in California, Washington, Oregon, and British Columbia, and the species is widely distributed in western and northern Europe. In Central America, the mushroom has been collected on the summit of Cerro de la Muerte in the Cordillera de Talamanca, Costa Rica, on leaf litter of Comarostaphylis arbutoides (a highly branched evergreen shrub or tree in the heath family). In 2010, it was reported from Hokkaido in northern Japan, where it was found growing on Picea glehnii forest litter in early winter. It has also been recorded from North Africa.