Nitrous bonnet

Appearance

The cap of ''M. leptocephala'' is 1–3 cm in diameter, and initially a fat conical shape with the margin pressed close to the stem. As the cap expands, it becomes broadly conic to convex, sometimes broadly bell-shaped, and sometimes convex with a flaring margin. The cap surface has a whitish sheen because of its pruinose coating. The coating gradually sloughs off, leaving the surface smooth and moist. The cap shows radial grooves that outline the position of the gills underneath. Its color is initially dusky brownish-gray to blackish , soon fading from dark to light gray and finally ashy-gray. The flesh is thin and fragile, grayish, and has a slightly sour taste, and a weakly alkaline odor that strengthens in intensity if the flesh is crushed. The gills are narrow, equal in width throughout, ascending-adnate and toothed. They are subdistantly spaced, with 18–27 gills reaching the stem, and one or two tiers of lamellulae interspersed between them. The color of the gills is pallid or cinereous, with pallid and even edges. The stem is 4–6 cm long, 1–2 mm thick, equal in width throughout, hollow, and very fragile. It is usually bluish-black initially but gradually turns sordid brownish-gray, and finally fades to pallid or cinereous. The surface is densely white-pruinose overall, but soon polished and translucent when the pruinose coating wears off. The stem base is nearly smooth to rather densely white-strigose. The species has a distinctive bleach-like odor. Its edibility is currently unknown.
The spores are broadly ellipsoid, amyloid , and measure 7–10 by 4–6 μm. The basidia are usually four-spored, although two- and three-spored forms have been found on which the spores measure 11–14 by 6–6.5 μm or 8–10 by 3.5–4.5 μm, respectively. The pleurocystidia are scattered, rare or absent, 30–44 by 9–13 μm, variable in shape, fusoid-ventricose to club-shaped, with some having a forked apex. The pleurocystidia that are club-shaped occasionally have two or three finger-like prolongations. The cheilocystidia are numerous, and similar in morphology to the pleurocystidia. The flesh of the gill is homogenous, composed of enlarged hyphae that stain vinaceous-brown in iodine. The flesh of the cap has a well-differentiated pellicle, the cells of which bear numerous rodlike prolongations. The hypoderm is well-formed, while the remaining tissue is floccose; all but the pellicle are vinaceous-brown in iodine stain.

Naming

The "stump fairy helmet" ''Mycena alcalina'' is a common species that is similar in appearance and odor to ''M. leptocephala''. However, it grows on conifer wood and rarely on the ground. Microscopically, it has numerous cystidia on the gill edges. Although ''M. leptocephala'' usually has a weaker alkaline odor and a more fragile stem, the strength of the odor of ''M. alcalina'' is also quite variable, so differences in odor cannot be used as the sole distinguishing characteristic. ''M. austera'', described from southern Norway in 1994, differs from ''M. leptocephala'' by the lack of a nitrous odor, and differently shaped cheilocystidia and terminal cells of the cortical layer of the stem. Alexander H. Smith considers ''M. brevipes'' close to ''M. leptocephala'', but the former mushroom has a short stem up to 3.5 cm long, typically grows singly, and lacks an odor.

Distribution

''Mycena leptocephala'' is a saprobic species, meaning it derives nutrients from the breakdown of organic matter. Fruit bodies are found growing scattered to gregarious on fallen sticks and on needle carpets under conifers, and are rather common during early summer and again in the autumn. Fruit bodies may be infected by the bonnet mold ''Spinellus fusiger''.

In North America, the fungus is found in Canada , to Washington and south to California and North Carolina. In South America, the mushroom has been collected in Venezuela. It also grows in the Archipelago of the Recherche, off the southern coast of Western Australia. In Europe, it is known from Britain, Finland, The Netherlands, Norway, and Spain It has also been found in various locations in Asia: the Vindhya Range of India; the Gwangneung Forest Museum in the Korea National Arboretum; and the alpine zone of Changbai Mountain Nature Reserve, Jilin Province, China. The fungus is also known from Arctic and Alpine regions such as Iceland, Greenland, and the Murmansk region.

Habitat

''Mycena leptocephala'' is a saprobic species, meaning it derives nutrients from the breakdown of organic matter. Fruit bodies are found growing scattered to gregarious on fallen sticks and on needle carpets under conifers, and are rather common during early summer and again in the autumn. Fruit bodies may be infected by the bonnet mold ''Spinellus fusiger''.

In North America, the fungus is found in Canada , to Washington and south to California and North Carolina. In South America, the mushroom has been collected in Venezuela. It also grows in the Archipelago of the Recherche, off the southern coast of Western Australia. In Europe, it is known from Britain, Finland, The Netherlands, Norway, and Spain It has also been found in various locations in Asia: the Vindhya Range of India; the Gwangneung Forest Museum in the Korea National Arboretum; and the alpine zone of Changbai Mountain Nature Reserve, Jilin Province, China. The fungus is also known from Arctic and Alpine regions such as Iceland, Greenland, and the Murmansk region.