Summary:
Cheimonophyllum is a segregate of Pleurotus. Features of this species are a small white dry cap that is sessile or with a short lateral stem, growth on wood, a white spore deposit, and round or nearly round spores. The online Species Fungorum, accessed July 16, 2019, gave the current name as Nothopanus candidissimus, but MycoBank, accessed the same day, gave the current name as Cheimonophyllum candidissimum.

Cap:
0.3-2cm broad, shell-shaped, inrolled at first, expanding to nearly flat; white covered with soft white hairs, with chalky appearance, soon becoming shriveled, (Brown), 0.5-2cm, rounded or kidney-shaped to shell-shaped, "elongating with age and becoming slightly strap-shaped", slightly undulate, margin incurved; brilliant white, discoloring cream when old; finely pubescent, nonstriate, (Watling), 0.15-2cm across, semicircular to kidney-shaped or shell-shaped, margin incurved at first; whitish; dry, minutely hairy, margin radially lined, (Lincoff), surface with a white layer of minute hairs on a yellowish background, margin becoming slightly striate when old, (Bessette), kidney-shaped, sometimes lobed; white; silky, (Courtecuisse), semicircular to spatula-shaped, delicate; chalk-white, (Barron)

Flesh:
thin, pliant; white, (Brown), very thin; white, (Watling), thin, soft; whitish to yellowish, (Bessette)

Gills:
reaching a point of attachment, subdecurrent [somewhat decurrent], broad, fairly distant, narrowing toward ends; white with chalky appearance; edges finely fringed or torn, (Brown), radiating from center or slightly eccentric point, crowded, thin; white, possibly flushed ivory or pale cream when old; slightly serrate on edge, (Watling), descending stem or attached to stem, distant, broad; white, (Lincoff), subdistant to fairly close, rather broad; white to yellowish, (Bessette)

Stem:
insignificant or absent, (Brown), "rudimentary, reduced to a central or lateral white hump, although even then demarcated from gills", (Watling), when present stub-like or lateral, (Lincoff), whitish (Bessette)

Veil:
no ring

Odor:
not distinctive (Bessette, Watling)

Taste:
not distinctive (Bessette, Watling)

Microscopic spores:
spores 5-6(6.5) x (4.5)5-5.5 microns, broadly elliptic to nearly round or short oval, smooth, inamyloid, acyanophilic, colorless, thin-walled; basidia 4-spored, 15-20 x 4-5.5 microns, clavate, colorless; pleurocystidia absent, marginal cystidia forming a sterile fringe of narrow, sometimes branched, hairs similar to those on cap cuticle and 2-3 microns wide, inamyloid; cap cuticle a collapsed intertwined turf of hyphae 2-3 microns wide, filamentous, thin-walled; clamp connections present, (Watling), spores 5-6 x 4.5-5.5 microns, round or nearly round, smooth, inamyloid, (Brown), spores 5-6 x 4.5-5.5 microns, round [or nearly round], smooth, colorless, (Lincoff)

Spore deposit:
white (Watling)

Notes:
It was reported from BC by Davidson(1) and there are collections from BC and YT at the University of British Columbia, from BC, WA and ID at the University of Washington, and from WA and OR at Oregon State University, (some collections under Pleurotus). It is encountered rarely in CA (Desjardin)

EDIBILITY

unknown (Bessette)

Synonyms and Alternate Names:
Pleurotus candidissimus (Berk. & M.A. Curtis) Sacc.