Summary:
Distinguishing characteristics include 1) a white stemless cap, 2) gills that are white at first, and close and narrow, 3) small, round, minutely spiny spores (4-5.5 microns in diameter), 4) no pleurocystidia, and 5) clavate to ventricose cheilocystidia. It is widely distributed and common. |Hesler(3) outlined 4 varieties: a) var. applanatus sensu Josserand (that description is below), b) var. phragmocystidiosus with septate cheilocystidia, c) var. diversus with different cheilocystidia and pilocystidia, which are forked, branched, or knobbed, and d) var. globigera with larger spores 4.5-7.5(8) microns in diameter.

Cap:
1-4cm, fan-shaped to petal-like, spathulate, kidney-shaped, or semi-orbicular [semi-circular]; hygrophanous, "white, becoming brownish or somewhat vinaceous to buff or dull cinnamon as spores mature"; bald, "at times more or less pubescent, villose or fibrillose at the base", margin striatulate [finely striate] when wet, (Hesler), 1-4cm, shell-shaped to petal-like; white, becoming brownish to cinnamon; moist, smooth or minutely hairy, (Lincoff), margin inrolled, faintly striate, (Miller)

Flesh:
thin; white, (Hesler)

Gills:
narrowly adnate-decurrent, close or crowded, narrow, subgills numerous; white, then brownish; edges fimbriate [fringed] to even, (Hesler), "radiating from point of attachment, close to crowded, narrow"; white, becoming brownish, (Lincoff)

Stem:
none (Phillips), attached to wood by hair-like strands (Lincoff), "absent, replaced by a short, white, hairy plug", (Miller)

Veil:
partial veil absent (Miller)

Odor:
mild (Hesler)

Taste:
mild (Hesler), with an unpleasant after-taste (Miller)

Microscopic spores:
spores 4-5(5.5) microns in diameter, larger in var. globigera (4.5-7.5 microns), round, punctate; basidia 4-spored, 22-27 x 6-7 microns; pleurocystidia none, cheilocystidia 20-40(50) x 5-10(12) microns, "clavate to ventricose, at times capitate"; cap tissue interwoven; cap cuticle of repent hyphae, at times with scattered erect hyphae and cystidia, 25-65 x 5-10(12) microns, clavate or ventricose; clamp connections present, (Hesler), spores 4-5.5 microns, round, minutely spiny, inamyloid, thick-walled, (Miller), spores without germ pore, (Lincoff)

Spore deposit:
"sayal brown" to "cinnamon brown", (Hesler, colors from Ridgway(1)), brown (Phillips), brownish to cinnamon-brown (Lincoff), red-brown (Buczacki)

Notes:
Schalkwijk-Barendsen reported C. applanatus from BC. Hesler(3) examined collections of var. applanatus from ID, MA, ME, MI, NC, NH, NY, OH, TN, VT, and France, of var. diversus from ON, QC, ME, and MI, of var. globigera from CA, MA, ME, MI, NC, NH, and TN, and of var. phragmocystidiosus from MI. The B. McAdoo photograph of var. globigera is from WA. The University of British Columbia has collections of C. applanatus (including var. applanatus) from BC. The University of Washington has collections from WA, ON, AK, IA, MI, NY, and VA. Oregon State has collections from OR. C. applanatus var. globigera is reported by B. McAdoo from WA.

EDIBILITY

no (Phillips)