The
cap is in diameter, and ranges in shape from conical to convex to bell-shaped. The surface has radially arranged shallow grooves extending almost to the center of the cap. The cap surface is somewhat
hygrophanous (changing color as it loses or absorbs water), dry, and smooth. It is colored violet-brown when young, then becomes somewhat paler from the margin. The white
flesh is up to 1 mm thick, and lacks any distinctive odor or taste. The
stem is long and slender compared to the size of the cap, typically tall by thick, cylindrical, slightly enlarged at the base, and hollow. It is grayish-brown to violet-brown at the top, gradually becoming violet-brown on the lower portion. The stem surface is initially
pruinose (appearing to be covered with a fine whitish powder), but becomes smooth in age. The stem base bears large, bristle-like coarse white hairs. The
gills are adnexed (narrowly attached to the stem), with between 23 and 27 reaching the stem. The gills are up to broad, thin, and have a whitish or with a grayish hue; the gills edges are the same color as the gill faces.
Microscopic characteristics The
spores are
ellipsoid, smooth, colorless, distinctly
amyloid (absorbing iodine stain from
Melzer's reagent), thin-walled, and measure 11.5–14 by 6–8
μm. The spore-bearing cells, the
basidia, are 17–28 by 6–8 μm, club-shaped, and four-spored. The basidioles (immature or aborted basidia) are club-shaped. The cheilocystidia (
cystidia found on the gills edges) are 32–39 by 5–12 μm, abundant, spindle-shaped to roughly club-shaped, often apically broadly rounded, smooth, colorless, and thin-walled. They form a sterile gill edge. Pleurocystidia (cystidia on the gill faces) are absent in this species. The
hymenophoral tissue (tissue of the
hymenium-bearing structure) is made of thin-walled hyphae that are 7–15 μm wide, cylindrical, smooth, colorless, and
dextrinoid (staining reddish to reddish-brown in Melzer's reagent). The
cap cuticle is made of parallel, bent-over hyphae that are 2–5 μm wide, cylindrical, and densely covered with warty or finger-like thin-walled diverticulae that are colorless or contain cytoplasmic brownish pigment. The layer of hyphae underlying the cap cuticle are parallel, colorless or with cytoplasmic brownish pigment, dextrinoid, and have short and inflated cells measuring up to 30 μm wide. The stem cuticle is made of parallel, bent-over hyphae that are 3–5 μm wide, and cylindrical. These hyphae are covered with scattered, thin-walled warty or finger-like
diverticulae that can be either colorless, or contain brownish
pigment in the
cytoplasm. The flesh of the stem is made of longitudinally running, cylindrical hyphae that are 5–17 μm wide, smooth, colorless, and dextrinoid.
Clamp connections are absent in all tissues of this species.
Similar species Mycena mustea is another similar
Mycena that was discovered and reported concurrently with
M. fonticola; it differs in forming a pale grayish purple cap with a low and broad
umbo. Microscopically, it has club-shaped cheilocystidia with several apical short finger-like outgrowths, and nondiverticulate hyphae in the stem cuticle. ==Habitat and distribution==