Summary:
Section Lactipedes (Smith), Section Sanguinolentae (Maas Geesteranus). Mycena sanguinolenta is characterized by 1) a dark reddish-brown to dark purplish brown to orange-brown cap, 2) marginate gills, 3) a stem that is the same color as the cap, has white hairs at the base, and exudes a dark red juice when broken, and 4) gregarious or tufted growth on leaf mold and needles. Smith described Mycena subsanguinolenta (which compared to M. sanguinolenta has more pronounced yellowish colors of the cap, stem, and juice, has smaller spores and lacks pleurocystidia), but Maas Geesteranus points out that M. sanguinolenta can have these colors in Europe, the spore size difference is questionable in the holotype, and M. sanguinolenta often has few or no pleurocystidia. The concept of Maas Geesteranus therefore includes M. subsanguinolenta.

Cap:
0.3-1.5(2.5)cm across, conic to bell-shaped or sometimes convex when old; color variable: some shade of pale reddish brown to bright reddish brown to orange-brown, etc., margin often vinaceous; smooth, not viscid, margin often furrowed at maturity, (Arora), 0.3-1(2.5)cm across, either convex or conic when young, becoming broadly convex or bell-shaped, "not expanding completely, margin appressed when young"; "color variable but always some shade of bright or dull reddish brown with a more or less vinaceous to avellaneous margin"; moist, at first with dense grayish hoary-pruinose coating, becoming bald, margin opaque or slightly striatulate, soon becoming sulcate [grooved], (Smith), 0.7-1.8cm across, parabolic or more conic to bell-shaped, with or without umbo; "dark red-brown, dark purplish brown to almost violet-brown when young", the center long remaining dark, paler further out, dingy pale brown, pale gray-brown, paler or darker flesh-color, the extreme margin frequently dark red-brown to purplish brown; dry but slightly lubricous when wet, delicately pruinose, becoming bald, more or less shallowly sulcate [grooved], translucent-striate, (Maas Geesteranus)

Flesh:
thin; "reddish, exuding a dark red juice when cut", (Arora), thin, not very fragile; "sordid reddish, exuding a reddish juice when cut", (Smith), thin; dingy brownish, (Maas Geesteranus)

Gills:
"attached (typically adnate), well-spaced"; "pallid or tinged flesh-color or reddish", edges dark reddish brown, (Arora), "adnate or slightly toothed, subdistant to distant, narrow to moderately broad"; "sordid reddish to grayish, the edges very dark reddish brown and even", (Smith), adnate, ascending, more or less decurrent with short tooth, 13-21 reaching stem, up to 0.1cm broad, somewhat ventricose [broader in middle]; "at first whitish, gradually turning pale dingy pink, pale brownish pink, pale purplish", the edge "dark red-brown, purplish brown, violet-brown"; smooth to faintly ribbed becoming dorsally interveined, (Maas Geesteranus)

Stem:
2-7.5cm x 0.1-0.2cm, "equal, hollow, fragile"; more or less cap-colored; smooth, "base with white hairs and exuding a dark red juice when broken or squeezed", (Arora), 2-6(7)cm x 0.1-0.15cm, "equal, tubular, fragile"; drab-pruinose becoming polished and more or less cap-colored; base with white hairs; exuding a bright or dull red juice when cut or broken, (Smith), 3-10cm x 0.05-0.15cm, equal for the greater part, hollow, round in cross-section, straight or curved in lower part, fragile to firm, the base at times somewhat rooting; brownish violet, brownish purple, very dark red-brown, darker or paler dingy flesh-color, paler in upper part, darker in lower part; smooth, innately fibrillose, sparsely purplish-puberulous [finely downy] all over, becoming bald for the greater part, "exuding a brownish red fluid when cut", base "more or less densely covered with long, coarse, woolly, whitish fibrils which turn reddish brown in the herbarium", (Maas Geesteranus)

Odor:
mild (Arora), not distinctive (Smith), indistinct or radish-like, (Maas Geesteranus)

Taste:
not distinctive (Smith)

Microscopic spores:
spores 8-11 x 4-6 microns, elliptic, smooth, weakly amyloid, cystidia present on gill faces and edges, (Arora), spores 8-10(11) x 4-5(6) microns, subelliptic (somewhat elliptic), only weakly amyloid; basidia 4-spored, occasionally 2-spored or 3-spored, pleurocystidia rare to scattered or sometimes quite abundant, 36-54 x 8-13 microns, narrowly to broadly fusoid-ventricose, filled with a sordid reddish substance, cheilocystidia abundant, similar to pleurocystidia or shorter and wider, (Smith), spores 8.1-10.0(11.0) x 5.4-5.8 microns, "pip-shaped, smooth, amyloid"; basidia 4-spored, 27-35 x 8-10 microns, clavate, clamped; pleurocystidia similar if present to cheilocystidia; cheilocystidia forming a sterile band, 27-55 x 6.5-10 microns, formed at the end of densely compacted vascular hyphae, "generally fusiform, simple and smooth, with reddish brown contents", clamped (but clamp connections difficult to see), apically narrowed into acute-tipped neck, but occasionally with 2 necks or with coarse lateral excrescences; hyphae of the cortical layer of the stem 1-3.5 microns wide, clamped, fairly sparsely covered with simple to forked cylindrical excrescences 1.8-4.5 x 1-2 microns, the terminal cells (caulocystidia) solitary to clustered, 18-55 x 5.5-9 microns, cystidia-like, (Maas Geesteranus)

Spore deposit:
white (Arora)

Notes:
Smith(1) examined collections from BC, WA, OR, MD, MI, NY, TN, and gives the distribution as from ME to WA and south to NC and CA in the US and from NS to BC in Canada, (as well as WA, OR, and CA for M. subsanguinolenta). Maas Geesteranus notes that it is known from Europe, North America, and Japan. Breitenbach(3) includes also North Africa and Australia.

EDIBILITY

unknown (Arora)

Synonyms and Alternate Names:
Mycena subsanguinolenta A.H. Sm.