Mycena galopus

Description

Mycena galopus is an inedible species of fungus in the family Mycenaceae of the order Agaricales. It produces small mushrooms that have grayish-brown, bell-shaped, radially-grooved caps up to 2.5 cm (1 in) wide. The gills are whitish to gray, widely spaced, and squarely attached to the stem. The slender stems are up to 8 cm (3 in) long, and pale gray at the top, becoming almost black at the hairy base. The stem will ooze a whitish latex if it is injured or broken.

This mushroom is found in North America and Europe. The saprobic fungus is an important leaf litter decomposer, and able to utilize all the major constituents of plant litter. It is especially adept at attacking cellulose and lignin, the latter of which is the second most abundant renewable organic compound in the biosphere. The mushroom latex contains chemicals called benzoxepines, which are thought to play a role in a wound-activated chemical defense mechanism against yeasts and parasitic fungi.

Common names: Milking Bonnet, Milk-Drop Mycena.

Mushroom Identification

1. Cap

   The cap is egg-shaped when young, later becoming conic to somewhat bell-shaped, and eventually reaching a diameter of 0.5 to 2.5 cm (0.2 to 1.0 in). In age, it often has a margin curved inward, and a prominent umbo. The cap surface has a hoary sheen (remnants of the universal veil that once covered the immature fruit body) that soon sloughs off, leaving it naked and smooth.

   The cap margin, which is initially pressed against the stem, is translucent when moist, so that the outline of the gills underneath the cap may be seen, and has deep narrow grooves when dry. The color is largely fuscous-black except for the whitish margin that fades to pale gray; the umbo remains blackish or becomes dark gray, sometimes with a very pale ashy gray overall when moist, and opaque and ashy gray after drying.

2. Flesh

   The flesh is thin, soft, and fragile, without any distinctive odor and taste.

3. Gills

   The gills are subdistantly spaced, narrow, ascending-adnate, whitish to gray, usually darker in age, with edges that are pallid or grayish.

4. Stem

   The stem is 4 to 8 cm (1.6 to 3.1 in) (rarely up to 12 cm) long, 1–2 mm thick, equal in length throughout, smooth, and fragile. The lower portion of the stem is dark blackish-brown to a dark ashy color. The apex of the stem is pallid, and the whitish base is covered with coarse, stiff hairs. When broken it exudes a white milk-like liquid. The variety candida is similar in appearance to the main variety, except its fruit body is completely white.

5. Microscopic Characteristics

   The spores are 9–13 by 5–6.5 μm, smooth, ellipsoid, occasionally somewhat pear-shaped, and very weakly amyloid. The basidia are four-spored. The pleurocystidia and cheilocystidia are similar and very abundant and measure 70–90 by 9–15 μm. They are narrowly fusoid-ventricose and usually have abruptly pointed tips, sometimes forked or branched near the apex, hyaline, and smooth. The flesh of the gill is homogenous and stains dark vinaceous-brown in iodine. The flesh of the cap has a thin but differentiated pellicle, a well-developed hypoderm (the tissue layer immediately underneath the pellicle), and the remainder is filamentous. All but the pellicle stain vinaceous-brown in iodine.

6. Similar Species

   The "red edge bonnet", Mycena rubromarginata, is also grayish-brown, but it has red gill edges, and it does not ooze latex when broken. It has amyloid, pip-shaped to roughly spherical spores that measure 9.2–13.4 by 6.5–9.4 µm.

History

When in 1799 Christiaan Hendrik Persoon described this bonnet mushroom, he called it Agaricus galopus.

German mycologist Paul Kummer transferred this species to the genus Mycena in 1871, thereby establishing its currently accepted scientific name Mycena galopus.

Since three varieties of this species are widely accepted, the autonomous form is referred to formally as Mycena galopus var. galopus (Pers.) P. Kumm.

The white form of this mushroom was described by Danish mycologist J. E. Lange in 1918 and is therefore formally referred to as Mycena galopus var. candida J. E. Lange. (Mycena galopus var. alba Rea is a synonym of Mycena galopus var. candida.)

The very dark form of this mushroom was described in 1922 by British mycologist Carlton Rea (1861 - 1946), and its formal name is therefore Mycena galopus var. nigra Rea. Its synonyms include Agaricus leucogalus Cooke, Mycena leucogala (Cooke) Sacc., Mycena galopus var. leucogala (Cooke) J. E. Lange, and Mycena fusconigra P. D. Orton.

The specific epithet galopus comes from the prefix gal- meaning milk and -pus referring to the leg or stem and is a reference to the fact that these bonnet mushrooms release a milk-like liquid from their broken stems.

Mycena galopus Chemistry

In 1999, Wijnberg and colleagues reported the presence of several structurally related antifungal compounds called benzoxepines in the latex of Mycena galopus. One of these compounds, 6-hydroxypterulone, is a derivative of pterulone, a potent antifungal metabolite first isolated from submerged cultures of Pterula species in 1997. The antifungal activity of pterulone is based on selective inhibition of the NADH dehydrogenase enzyme of the electron transport chain.

A 2008 publication reported that fatty acid esters of benzoxepine serve as precursors to wound-activated chemical defense. When the fruit body is injured and the latex is exposed, an esterase enzyme (an enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis) presumably cleaves the inactive esterified benzoxepines into their active forms, where they can help defend the mushroom against yeasts and parasitic fungi. In nature, the mushroom is rarely attacked by parasitic fungi, however, it is prone to infection by the "bonnet mold" Spinellus fusiger, which is insensitive to the benzoxepines of M. galopus.

In an English field study, where the two fungi M. galopus and Gymnopus androsaceus made up over 99% of the fruit bodies in a site under Sitka spruce, the fungivorous collembolan arthropod Onychiurus latus preferred to graze on the mycelium of M. androsaceus. This selective grazing influences the vertical distribution of the two fungi in the field.

Video

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