Summary:
Leucoagaricus americanus is easily recognized, according to Arora(1) "by its tendency to darken to reddish or burgundy as it ages or dries, and the yellow to orange staining of fresh specimens (best seen by cutting the stalk). In addition, the shape of the stalk is quite unusual - often very slender at the apex and blatantly bulbous at or toward the base". Vellinga says, "the shape of the stem is quite constant and always fusiform [spindle-shaped]. When cut, all show first a yellow discoloration, followed by red: all turn a vinaceous pink on drying." Other features include a pinkish buff to reddish brown disc, toward the margin with scales of similar color on a background that is white at first but often reddening when old; free, close gills that are white at first but may discolor like the flesh; a stem that is whitish and appressed-silky-fibrillose; a membranous ring; growth particularly on wood or wood products like sawdust or wood-chips; and dextrinoid spores.

Cap:
(3)6-15cm across, ovoid becoming bell-shaped or flat, sometimes with an umbo; pinkish buff to reddish brown; disc unbroken, margin "with slightly upturned scales the color of the disc, pale flesh exposed between the scales", (Sieger), 3-15cm across, oval becoming convex, flat, or broadly umbonate; dry, smooth then breaking into coarse, vinaceous brown to reddish brown or pinkish buff scales, the center usually remaining smooth, background white but often reddening when old, (Arora), 3-15cm across, ovate, obtuse, or almost truncate becoming broadly convex or nearly flat and umbonate; "pinkish buff" to "tilleul buff", soon reddish or bay brown, 'whitish between scales when young and fresh but becoming dingy red in age or when bruised'; 'cuticle at first continuous, the disc dull and unpolished, at times slightly scaly, remainder ruptured into large scattered scales', when old becoming appressed-fibrillose-scaly to lacerate-scaly, more or less striate on margin, dry herbarium specimens are smoky red (the whole fruitbody), (Smith, H.V. who notes that according to Kauffman the cap may sometimes be almost entirely white when fresh); margin deeply grooved when mature (Kibby)

Flesh:
pale, "bruising bright yellow fading to orange, orange red, and finally dull reddish brown to vinaceous brown, but older specimens may develop only the final colors", (Sieger), "white, bruising yellow to orange when young and fresh" (especially in stem), "but aging or drying reddish to vinaceous", (Arora), thick, very firm; white, becoming buff or reddish when old or when bruised, according to Kauffman flesh may have a yellow tinge at first, (Smith, H.V.)

Gills:
free, close; cream to pale yellow; edges finely fringed, (Sieger), free, close; "white, but may stain or age like the flesh", (Arora), at first approximate to stem, "sometimes becoming remote and attached to a collar", horizontal to ascending, broad, 0.5-1cm broad, broader toward cap margin, thin, 2 tiers of subgills; "white, often darkening to pinkish buff" (according to Kauffman may have a yellow tinge at first), edges white; edges fimbriate [fringed], (Smith, H.V.)

Stem:
(7)8-12cm x (0.6)1.2-2.2(4)cm at widest point, sometimes club-shaped or cylindric but usually spindle-shaped - widest just below midpoint, often pointed at base; whitish in upper part, pale to brownish in lower part; smooth in upper part, smooth or slightly fibrous in lower part, often with "roots" at base, (Sieger), 7-14cm x 0.5-2cm, widened at base or often spindle-shaped (swollen at or below middle, with narrowed base); "at first white, but aging or drying reddish to dark vinaceous"; smooth, (Arora), 7-12cm x (0.4)0.8-2.2cm at top, clavate to somewhat bulbous at base or at times fusiform [spindle-shaped], hollow, stuffed; "staining yellowish or reddish and finally sordid reddish buff after handling"; appressed-silky-fibrillose, (Smith, H.V.)

Veil:
membranous, usually persistent, "flaring like a collar when young", above whitish, lower margin colored and staining like cap, (Sieger), membranous, forming white, double-edged, superior ring that may disappear when old, (Arora), ring "superior, double, rather large, flaccid, sometimes moveable and sometimes evanescent, whitish in general but often cracked into sordid patches below", (Smith, H.V.)

Odor:
not distinctive (Sieger, Smith, H.V.)

Taste:
not distinctive (Sieger, Smith, H.V.)

Microscopic spores:
spores 8.4-10.4 x 5.8-7.2 microns, in side view elliptic "with in many cases more convex abaxial side than adaxial side", some slightly amygdaloid [almond-shaped], in face view elliptic, [presumably smooth], dextrinoid, with thick wall, with germ pore, congophilic, metachromatic in cresyl blue, cyanophilic, often pale green-yellow in ammonia; basidia 4-spored, a very few 2-spored, 21-26 x 7.5-10 microns; pleurocystidia absent, cheilocystidia rendering gill edge sterile, 36-65 x 12-19 microns, "narrowly clavate, clavate, clavate-fusiform, rarely without, often with moniliform or cylindrical, sometimes capitulate, apical excrescence", 2.0-50 x 2.0-5.0 microns, with up to 10 microns wide capitulum, with green-brown contents in ammonia; clamp connections not observed, (Vellinga(1)), clamp connections present (H.V. Smith), spores (7.9)9-10.5(12) x 6.3-7.5(9) microns, elliptic to oval, with a small germ pore, pleurocystidia absent, cheilocystidia abundant, cap cuticle "interwoven to ascending hyphae, many cells slightly inflated, upper cells often pale brown", (Sieger), spores 8-14 x 5-10 microns, elliptic, smooth, dextrinoid, thick-walled, with apical pore, (Arora)

Spore deposit:
pale cream (Sieger), white (Arora)

Notes:
There is a collection from BC at the University of British Columbia (as Lepiota). There are collections from WA, NY, and NC at the University of Washington. Vellinga(5) used material from MI and NC. It has been found relatively rarely in CA (Desjardin).

EDIBILITY

edible if sure of identification, similar fungi are poisonous, (Arora), edible for most people, reddens urine, (Sieger)

Synonyms and Alternate Names:
Lepiota americana Peck
Leucoagaricus bresadolae Schulzer) Bon
Leucocoprinus americanus (Peck) Redhead
Leucocoprinus bresadolae Schulzer) Wasser