Summary:
Marasmiellus pluvius is characterized by a soft, fragile, putrescent fruiting body with a brownish orange to pale orange cap, white gills, an insititious pruinose stem pale at top and red-brown at base, fruiting on needles, and distinctive cheilocystidia (vesiculose with numerous long, irregularly cylindric diverticula). There are problems with its placement in Marasmiellus and it is likely to end up in a different genus.

Cap:
0.5-1.2cm across, hemispheric becoming flat to depressed and rugose [wrinkled] when old; "whitish with buff to honey tints centrally"; at first dry and opaque, translucent-striate and moist when old, (Redhead(29)), 0.5-1.2cm across, convex or flat-convex; pale orange to brownish orange, remaining so or fading to grayish orange when old (margin colored as the rest of the cap when young, becoming grayish orange, pale orange-white or pale cream-buff when old); bald, dull, opaque, margin even when young, becoming wavy, subrugulose [somewhat wrinkled] and [short-grooved], (Desjardin)

Flesh:
submembranous; colored as cap, (Redhead(29)), thin; white or buff, (Desjardin)

Gills:
adnate, moderately spaced to distant, moderate breadth, ventricose [broader in middle] when old, subgills in 2-3 tiers; whitish to buff on faces, whitish on edges, (Redhead(29)), "adnate or adnexed, close or subdistant", 2 tiers of subgills, broad, rarely interveined; white or pale pinkish white when young, pale cream or pale orange when old, (Desjardin)

Stem:
1.4-3cm x 0.08-0.1cm, narrowing downwards, insititious, subcartilaginous, hollow; whitish to buff at top, sienna to fulvous on mid-part, dark brick to fuscous black at base; "powdered to scabrous overall, increasingly rough toward the base", (Redhead(29)), 1.8-2.5cm x 0.1-0.2cm, equal or flared at top and narrowing downward, round in cross-section or rarely compressed, insititious; white or buff or pale orange at top, brownish orange or brown in mid-part, brown or reddish brown at base; pruinose or glabrescent [becoming bald], (Desjardin)

Odor:
not distinctive (Redhead(29)), mild (Desjardin)

Taste:
not distinctive (Redhead(29)), mild (Desjardin)

Microscopic spores:
spores 8.5-10.5 x 2.3-4.0 microns, narrowly elliptic to narrowly fusoid (spindle-shaped), smooth, inamyloid, colorless, thin-walled, often multiguttulate [with several droplets inside], with prominent apiculus; basidia 4-spored, 20-21 x 5.9-6.3 microns, clavate, with clamp connection; cheilocystidia "abundant, and compactly arranged, forming a thickened sterile edge", 33-60 x 11-19 microns, mostly vesiculose-pedicellate "but with some more elongated clavate forms filling in gaps, densely covered with short papillae or more often with vermiform apical projections which occasionally branch"; gill trama: hyphae like the cap trama hyphae; pileipellis "a compactly interwoven layer of densely diverticulate hyphae" 4-12 microns wide, with clamp connections, "vaguely incrusted and pale brownish, walls slightly thickened or thin", cap trama: hyphae 4-9 microns wide, interwoven, smooth, with clamp connections, with slightly thickened walls, inamyloid; caulopellis: hyphae 4-6 microns wide, "with brownish, smooth, thickened walls", caulocystidia "abundant, usually clustered", 13-55 x 8-13 microns, polymorphic, varying from a simple ventricose to ellipsoid cell to sparsely coralloid or vermiform shapes, mostly with slightly thickened colorless walls, stem trama: hyphae 4-12 microns wide, parallel, thick-walled, smooth, colorless, with clamp connections, (Redhead(29)), spores 9-11.2(12) x 2.4-3.2 microns, long-elliptic or subfusiform (somewhat spindle-shaped); basidia 2-spored or 4-spored, 17-20 x 6-7 microns, clavate; pleurocystidia absent, cheilocystidia abundant, 25-33 x 10.2-21 microns, clavate, vesiculose or irregular, diverticulate, diverticula numerous, 3.6-21 x 0.9-3 microns, "filamentous or irregularly cylindric, often branched, apical and subapical", often gelatinizing when old; cap cuticle a well developed and continuous Rameales-structure of two types of elements: 1) "repent, diverticulate hyphae, non-incrusted, non-gelatinizing", colorless or pale yellow, "inamyloid, thin-walled", "diverticula numerous, rod-like, knob-like, or branched", 2) "scattered, thick-walled, clavate or vesiculose elements 10.2-16.8 microns broad with long rod-like projections"; tramal hyphae inamyloid; caulocystidia "15-27 x 5.4-12 microns, broadly clavate, lecythiform, mucronate, or short-cylindric, obtuse, often with short, knob-like projections", colorless, "inamyloid, thin-walled", (Desjardin)

Spore deposit:
[presumably white or whitish]

Notes:
It has been found at least in BC (where it is a common species on needle beds in the Vancouver region), (Redhead). It also occurs in CA (Desjardin). There are collections from WA at the University of Washington.

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