Mycena galopus, commonly known as the milky mycena, milking bonnet or milk-drop mycena, 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. The variety nigra has a dark gray cap, while the variety candida is white. All varieties of the mushroom occur during summer and autumn on leaf litter in coniferous and deciduous habitats. Mycena galopus 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.
Taxonomy The mushroom was first described as Agaricus galopus by Christian Hendrik Persoon in 1800, and later transferred to the genus Mycena by Paul Kummer in 1871. An Australian taxon formerly considered a variety, Mycena galopus var. mellea, was raised to species level and renamed M. thunderboltensis in 1998. The variety candida was described by Jakob Emanuel Lange in 1914 based on specimens he found in Denmark; variety nigra was named by Carleton Rea in 1922. Mycena galopoda is an orthographical variant spelling. The specific epithet galopus is derived from the Greek γαλα "milk", and πονς "foot". The mushroom is commonly known as the "milking bonnet", or the "milk-drop Mycena". The varieties candida and nigra are the white and black milking bonnets, respectively.
Description
The cap of M. galopus 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 over all when moist, and opaque and ashy gray after drying. The flesh is thin, soft, and fragile, without any distinctive odor and taste. The gills are subdistantly spaced, narrow, ascending-adnate, whitish to gray, usually darker in age, with edges that are pallid or grayish. 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 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. Variety nigra has a dark or blackish-gray cap, and gills that are initially whitish before turning gray. Although not poisonous, M. galopus and the varieties candida and nigra are inedible.
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 homogeneous, and stains dark vinaceous-brown in iodine. The flesh of the cap has a thin but clearly 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.
Similar species The "red edge bonnet", M. rubromarginata, is also grayish-brown, but it has gill edges that are red, 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.
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