Hyménomycètes: 266. 1876
Common Name: none
Cap (5) 10-20 mm broad, obtuse-conic, broadly so in age, sometimes campanulate, often with a low umbo; margin decurved, entire in youth, occasionally becoming crenate to eroded; surface moist, glabrous, hygrophanous, translucent-striate to sulcate-striate to near the disc, the latter with a sparse bloom when young, color brown, yellowish brown, to yellow, darker at the disc, fading with age; context thin, approximately 1 mm thick, buff to watery brown; odor and taste raphanoid.
Gills close, ascending-adnate to slightly notched, descending the stipe apex a short distance as lines; up to 3 mm broad, pale greyish tan, maturing buff to pale tan, sometimes intervenose in age, edges marginate, pinkish brown, light brown, to yellowish; lamellulae in up to two series.
Stipe 10-40 x 1-1.5 mm thick, fragile, cylindrical, to slightly enlarged at the base, hollow in age, surface of apex inconspicuously pruinose, striate from gill edges, elsewhere glabrous or with innate fibrils, dingy pinkish tan, darker towards the base, the latter sparsely covered with soft white hairs; partial veil absent.
Spores 8-12.5 x 4-5.5 µm, ellipsoid, smooth, thin-walled, hilar appendage not conspicuous, amyloid; spores white in deposit.
Scattered to gregarious in urban grassy areas, e.g. lawns, cemeteries etc.; in grass in montane seepage areas; also in mixed coastal forests and the Sierra Nevada; reported under Sitka spruce (Picea sitchensis), lodgepole pine (Pinus contorta), and white fir (Abies concolor), as well under hardwoods; fruiting after fall rains along the coast and after snowmelt in the Sierra Nevada; occasional to locally common.
Mycena citrinomarginata is a chameleon-like species, varying in color from yellow to brown and occupying habitats from grass to forest. Whether these differences are genetic and represent ecotypes (three varieties have been described) or responses to environmental factors, is a subject of debate. The above description fits what is most commonly found in the San Francisco Bay Area where it fruits in grassy areas, usually close to trees. In this habitat it is characterized by conic-obtuse caps that are brown at the disc, shading to a lighter margin, and gill edges that are pinkish brown to light brown. A radish-like odor is also a useful field-mark. Montane forms typically have a yellowish cap and yellowish marginate gills, the basis of the species epithet. Complicating matters is another Mycena, M. olivaceomarginata. With cap colors that overlap with those of Mycena citrinomarginata and similar micromorphology, it may be conspecific. If confirmed by molecular study, then M. citrinomarginata, an older name, has priority. In coastal and montane forests, yellowish fruitings of Mycena citrinomarginata should be compared with M. epipterygia, a yellowish to yellow-olivaceous cap species that has a viscid, not moist cap, and non-marginate gills. The brown form of Mycena citrinomarginata bears a resemblance to a number of forest Mycenas, perhaps the most similar, Mycena galopus. It, however, lacks marginate gills, a radish odor, and exudes a milky juice at the base of the stipe when injured.
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