Summary:
Marasmiellus papillatus is characterized by 1) small size, 2) a dry, frosted cap that is rosy buff to wine-colored, 3) whitish gills, 4) a dry, silky to frosty stem that is whitish to rosy buff or buff in upper part and cinnamon to dark brick in lower part, 5) growth on decorticated wood, 6) a white spore deposit, and 7) microscopic characters. There are problems with its placement in Marasmiellus and it is likely to end up in a different genus. Redhead and Halling include Marasmius alienus Peck and Marasmius umbilicatus Kauffman in their concept of this species.

Cap:
0.5-1.9cm across, convex with incurved margin, becoming flat-convex to depressed; "at first rosy buff to dark vinaceous with paler margins, soon fading to whitish with rosy buff to cinnamon tints centrally"; "overall frosted opaque appearance" except old expanded caps vaguely translucent-striate, usually prominently rugose [wrinkled], when old sometimes radially furrowed, (Redhead(28)), 0.5-1.5cm across, convex-expanded, markedly papillate; dingy whitish with pink tinge; slightly fine-hairy or bald, striate on margin (Kauffman), 2-4cm across, umbilicate (with an abruptly depressed disc), when old the margin uplifted; "white over most of surface", but "disc at times tinged pinkish gray", (Smith(6)), 2-4cm across, not usually umbilicate; "dull white except for very young stages which are pale buff"; "more or less wrinkled", (Smith(8))

Flesh:
tough, submembranous; colored as cap, (Redhead(28)), somewhat membranous (Kauffman)

Gills:
"adnate usually with a decurrent tooth", becoming more decurrent with age, moderate breadth to moderately narrow, subdistant at times, rarely forked; "faintly buff to rosy buff to nearly white", (Redhead(28)), decurrent tooth, close to subdistant; whitish or tinged yellowish (Kauffman), +/- decurrent, close then subdistant, narrow; whitish, (Smith(6)), subdistant, narrow; whitish, (Smith(8))

Stem:
2-4.3cm x 0.08-0.35cm, equal or narrowing in lower part, round in cross-section or flattened; pale in upper part, whitish to rosy buff or buff apically [at top], "cinnamon to dark brick basally"; silky to frosty, (Redhead(28)), 2-5cm long and about 0.1cm wide, equal, elastic, toughish, hollow, distinctly rooting; pallid tinged flesh color, slightly darker below; pruinose, (Kauffman), 3-7cm x 0.2-0.4cm, more or less equal; "pinkish brown to dark smoky brown over lower part", pallid near top, "base with brownish tomentum", longitudinally sulcate [grooved] at times, (Smith(6)), 3-8cm x 0.15-0.35cm, dull white at top and finally dark brown in lower part; "white pruinose and unpolished", (Smith(8))

Odor:
not distinctive (Redhead(28), Smith(8))

Taste:
"vaguely bitter or not distinctive", (Redhead(28)), not distinctive (Smith(8))

Microscopic spores:
spores 8.2-13 x 3.3-4.1 microns, cylindric to elliptic, smooth, inamyloid, "with thin but pronounced walls, prominently apiculate"; basidia 4-spored, 33-50 x 5.2-6.3 microns, elongate-clavate, with clamp connection; pleurocystidia and cheilocystidia "abundant, prominently projecting", usually shorter toward the gill edges, 43-90 x 4.5-9.5 microns, "narrowly fusoid to fusoid-ventricose, often with an elongated pedicel", occasionally subcapitate and/or vaguely strangulate, "smooth, with pronounced walls"; gill trama: hyphae similar to cap hyphae, more compactly arranged; pileipellis composed of hyphae 2-4 microns wide, interwoven, filamentous, smooth, thin-walled, with clamp connections, with dense cytoplasm, "bearing a dense turf or tangle of contorted to coralloid hyphal ends when young, the layer of diverticulate elements less obvious after cap expansion and aging", cap trama: hyphae 4.5-9 microns wide, compactly to loosely interwoven, colorless, inamyloid, smooth, slightly thick-walled, with clamp connections; caulopellis: "hyphae less inflated than tramal hyphae, bearing scattered to clustered caulocystidia", which are numerous, intermediate in form between the pleurocystidia and the cap elements, 48-55 x 4-5 microns, "narrowly fusoid to filamentous, usually contorted, occasionally branched, with refractive walls, occasionally septate", stem trama: hyphae 3-12 microns wide, parallel, slightly thick-walled, with clamp connections, colorless, often densely cytoplasmic; basal mycelium: hyphae 2-3 microns wide, smooth, colorless, thick-walled, with clamp connections, often undulating, (Redhead(28)), spores 10-11 x 3-4 microns, subcylindric, smooth, inamyloid; cystidia few, scattered, about 50 x 5-6 microns, narrowly lanceolate (lance-shaped, many times longer than broad, and tapering), acuminate (gradually narrowed to a point), (Kauffman), spores 9-12 x 3-4.5 microns, subcylindric, (Smith(6)), spores 9-12 x 3-3.5 microns, narrowly subfusoid in face view, pointed at apiculate end, smooth, inamyloid, thin-walled; basidia 4-spored; pleurocystidia and cheilocystidia 50-72 x 5-8 microns, acicular to subfusoid, smooth, thin-walled, colorless in KOH, (Smith(8))

Spore deposit:
white (Redhead(28), Smith(8))

Notes:
Collections were examined from BC, ON, MI, NY, and PA, and it has been recorded also from WA, OR, ID, and ME, (Redhead(6)).

EDIBILITY

Synonyms and Alternate Names:
Marasmius papillatus Peck