Nitrous Bonnet

(Mycena leptocephala)

Conservation Status
Nitrous Bonnet
Photo by Honey Fae (Farah)
  IUCN Red List

not listed


NNR - Unranked


not listed


Nitrous Bonnet is a small, fragile, gray, gilled mushroom. It occurs in Europe, Asia, New Zealand, Chile, and North America. In the United States it occurs in the east from Maine to North Carolina, west to Minnesota and eastern Texas. In the west it occurs west of the Rocky Mountains from northern Washington to southern California. It also occurs in Alaska, and there are scattered populations from Idaho south to Arizona and New Mexico. It is found alone, scattered, or in groups but not clustered (gregarious), in coniferous and mixed woodlands. It fruits from spring through fall but especially in spring to early summer and in late fall. It grows on the ground on coniferous debris, including sticks, needle carpets, and cones. It obtains its nutrients from decaying wood (saprobic).

When it first appears, the cap is broad but cone-shaped, and black to dark grayish-brown. The upper surface is densely covered with fine white powder, and the margins are pressed closely to the stalk. As it ages the cap flattens out, the powder wears off completely, and the color fades. The mature cap is broadly cone-shaped, convex, or broadly bell-shaped. It is usually to 1¼ (1 to 3 cm) in diameter, sometimes up to 1½ (4 cm) in diameter. The upper surface is grayish-brown or gray, free of powder, moist, and strongly lined. The margins are whitish.

The gills are narrow and moderately well spaced. There are 18 to 27 main gills, and between the main gills there are one or two series of short gills that do not extend to the stalk. The main gills curve upward approaching the stalk and are either narrowly attached to the stalk or are attached with a tooth that extends slightly down the stalk. The gills are whitish or pale gray with whitish edges.

The stalk is fragile, hollow, 1¼ to 2¾ (3 to 7 cm) long, and 132 to (1 to 3 mm) thick, equal in size from top to bottom. It is black to dark brown and covered with whitish powder at first. As it ages it fades to grayish or brownish and becomes free of powder.

The flesh is thin, fragile, and grayish. It has a mild odor of bleach that becomes strong when the flesh is crushed. It is not known if it is edible, but the taste is acidic and unpleasant.

The spore print is white.


Similar Species

Habitat and Hosts

Coniferous and mixed woodlands. Debris of conifers.




Spring through fall


Distribution Map



4, 24, 26, 29, 30, 77.




Not common in Minnesota

  Kingdom Fungi (fungi)  
  Subkingdom Dikarya  
  Phylum Basidiomycota (club fungi)  
  Subphylum Agaricomycotina (jelly fungi, yeasts, and mushrooms)  
  Class Agaricomycetes (mushrooms, bracket fungi, puffballs, and allies)  
  Subclass Agaricomycetidae  
  Order Agaricales (common gilled mushrooms and allies)  
  Suborder Marasmiineae  




Mycena (bonnets)  



Agaricus alcalinus ssp. leptocephalus

Agaricus leptocephalus

Mycena alcalina var. chlorinella

Mycena chlorinella


Common Names


Nitrous Bonnet












A term often used for saprotrophic fungi. Referring to fungi that obtain their nutrients from decayed organic matter.





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Honey Fae (Farah)

    Nitrous Bonnet      








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Other Videos
  Mycena alcalina and Mycena leptocephala are very similar
Paul Stamets

Nov 10, 2019

Mycena alcalina and Mycena leptocephala are very similar, sharing the strong smell of chlorine (bleach) when crushed. When we tested specimens for chlorine, none was found.

Many questions naturally come to mind.

Is this chlorine-mimicking smell attractive to certain insects that help it spread spores? Or conversely, to repel insects from predating upon them? Why would a mushroom out-gas such a distinctive odor? Is it non-consequential? Humans have a tendency to find meaning in nature when there may be none.

In my mind, at this stage in evolution, the presence of such strong chlorine-mimicking molecules is likely related to relationships these species have that are beyond our present knowledge. .

I initially thought that this species might be a good candidate for breaking down chlorine-bound toxins, like PCB’s (polychlorinated biphenyls). The work we did with Battelle Laboratories and New Fields (with Dr. Jack Word), revealed that many white rot fungi could decompose’ PCB’s if the PCB’s were the predominant “nutrient” in the media. However, when we inoculated PCB contaminated soil, the mycelium prefers other easy-to-digest foods. Nevertheless, a good example of epigenesis - that we could train a fungal strain to up-regulate genes to code for enzymes that have a talent for detoxifying these carcinogens.




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  Honey Fae (Farah)
October, 2021

Location: Hennepin County

Nitrous Bonnet







Created: 12/10/2022

Last Updated:

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