Summary:
Marasmius oreades is distinguished by a light brownish cap that is often obtusely umbonate, broad white to buff gills that are fairly well spaced and not decurrent, a thin, tough stem, growth in grass, a white spore deposit, and the ability of dried specimens to revive dramatically when moistened. It is common in the Pacific Northwest in grass. The online Species Fungorum, accessed January 28, 2016, gave the current name as Marasmius oreades (Bolton) Fr., including among the synonyms the proposed current name Scorteus oreades (Bolton) Earle ex Redhead.

Cap:
1-5(6)cm across but usually 2-4cm, "at first bell-shaped or umbonate with an incurved margin", then convex or flat "but often retaining an obtuse umbo", the margin often uplifted when old; reddish tan "to light brown, tan, buff, or even white"; smooth, dry, "margin faintly striate when moist", (Arora), 2-4cm across, bell-shaped or convex when young, flat-convex and broadly umbonate when old, often with an uplifted margin; disc brown when young, light brown or paler when old, margin light brown at first, fading to cream or buff when old; bald, dull, smooth or minutely rugulose [finely wrinkled], (Desjardin), deep brown in primordia, then light yellowish brown or light grayish brown, hygrophanous and fading to light yellowish brown or yellowish white, occasionally tinged grayish red in bruised areas, rarely light yellow or light yellowish pink or grayish red or dark reddish brown overall, (Gilliam)

Flesh:
tough, pliant, reviving when moistened; pallid, (Arora), 0.2-0.4cm thick, white or buff, (Desjardin)

Gills:
"adnate, adnexed or free, fairly well-spaced, broad"; white to pale tan, sometimes discoloring brownish when old, (Arora), "adnexed, subdistant, broad", rarely forked or interveined, 1-3 tiers of subgills; yellowish white or orange white, (Desjardin), adnexed to free, close to distant, 20-28 reaching stem, 1-5 tiers of subgills, narrow at first but in age up to 0.5cm broad, interveined or not, rarely forked, (Gilliam)

Stem:
2-8cm x 0.15-0.6cm, equal or narrowing downward, tough, pliant; "colored like the cap or paler (whitish)"; smooth, (Arora), 2-7cm x 0.3-0.5cm, equal or subclavate [somewhat club-shaped], round in cross-section, often with a short root-like pseudorhiza, fibrous, not insititious; top buff or yellowish white, base yellowish white, orange white, or dingy grayish orange; top pubescent [finely hairy], "base felted or tomentose", (Desjardin), solid or stuffed, even or with twisted longitudinal ribs, "tomentose, hirsute, minutely felted, or fibrillose-squamulose basally or overall", basal mycelium inconspicuous; rhizomorphs and sterile stems lacking, (Gilliam)

Veil:
partial veil absent (Miller)

Odor:
agreeable (Arora), of cyanide or chlorine, (Desjardin), pleasant to almond-like (Phillips), of cyanic acid, faint or strong, (Gilliam), fragrant (Miller)

Taste:
mild (Desjardin), pleasant (Phillips), mild or lacking (Gilliam)

Microscopic spores:
spores 7-10 x 4-6 microns, elliptic to somewhat irregular, smooth, inamyloid, apiculate, (Arora), spores 6.6-9 x 3.9-6 microns, broadly elliptic, almond-shaped, or lemon-shaped; basidia 4-spored, 32-40.2 x 6-8.1 microns, clavate or spheropedunculate; pleurocystidia and cheilocystidia absent; cap cuticle hymeniform, cells 20-33 x 3.6-12 microns, cylindric, clavate, or spheropedunculate, "rarely strangulate, often lobed (bifid)", with colorless or pale yellow, inamyloid or weakly dextrinoid walls up to 1 micron thick, tramal hyphae colorless or pale yellow, dextrinoid; cortical layer of stem 150-200 microns thick, "of interwoven hyphae with strongly dextrinoid walls up to 1 micron thick", caulocystidia abundant, often clustered, 40-130 x 3-12 microns, "repent or erect, filamentous, clavate, or strangulate", colorless or pale yellow, "with strongly dextrinoid walls up to 1 micron thick"; clamp connections present, (Desjardin), spores (6.3)7.0-10.0 x 3.5-6.0 microns, oboval, ovate, lemon-shaped, fusoid-elliptic, or rarely nearly round; basidia 33-45 x 5.5-8.5 microns, "subclavate to clavate, with a long, narrow basal portion", basidioles clavate, (Gilliam)

Spore deposit:
white (Arora), white to buff (Miller)

Notes:
There are collections from BC at the University of British Columbia. There are collections from WA, OR, ID, ON, AK, IA, MI, NE, and NY at the University of Washington. There are collections from OR, OH, and SD at Oregon State University. Arora(1) finds it in CA. It occurs also in Europe.

EDIBILITY

delicious, discard stems, but make sure it is not Clitocybe rivulosa (see similar), (Arora), adverse reactions in individuals have been recorded (Phillips)

Synonyms and Alternate Names:
Scorteus oreades (Bolton) Earle ex Redhead