Synonyms: Agaricus americanus Peck; Lepiota americana (Peck) Sacc.; Lepiota bresadolae Schulzer
Cap 5.0-9.0 cm broad, obtuse-conic, becoming campanulate to convex, at maturity nearly plane, umbonate through most stages of development; margin incurved to decurved, often upturned in old specimens; cuticle minutely tomentose (use hand-lens), cinnamon-brown to dull reddish-brown, darkening where handled, remaining intact at the disc, elsewhere breaking up into appressed scales, revealing a whitish context, the latter soft, relatively thin, 0.5 cm thick at the disc, sporadically yellowing, then orange-brown; odor not distinctive to slightly pungent; taste untried.
Lamellae Gills free, close to crowded, broad, up to 1.0 cm wide, white to cream, the edges bruising pinkish-orange, becoming tawny-brown; lamellulae up to four-seried.
Stipe 7.0-12.0 cm long, up to 2.0 cm thick, fusiform to clavate, hollow or stuffed in age; surface of apex appressed fibrillose, pallid, becoming more coarsely appressed fibrillose below, the fibrils dull-brown over a pallid ground color; surface yellowing where handled, eventually dark reddish-brown to brown; context discoloring like the stipe surface; partial veil membranous, white, the margin felty-floccose, brownish with age, forming a superior, evanescent annulus.
Spores 8.0-10.0 x 6.0-7.5 µm, elliptical in face-view, slightly inequilateral in profile, smooth, moderately thick-walled, with an apical germ pore, weakly dextrinoid in Melzers reagent, hilar appendage inconspicuous; spore print cream-colored.
In small groups to clustered on wood chips, edges of sawdust piles, and lignin-rich soil; fruiting in late summer in watered areas and early in the mushroom season; rare.
Edible, but too infrequent to be of culinary value; see "Comments" regarding related toxic species.
Leucoagaricus americanus is found commonly in the Midwest and Eastern U.S., but is rare in California, the few collections known coming mostly from wood chips in urban areas. A medium-sized mushroom, it is recognized by a pinkish-brown to reddish-brown, squamulose, umbonate cap, and a fusiform to club-shaped stipe. Also characteristic are color changes that occur when the flesh is injured: at first yellowish, then reddish-brown to brown. Dried specimens are distinctive, turning entirely vinaceous-brown. Leucoagaricus americanus is distantly related to several toxic species, Chlorophyllum molybdites, Lepiota helveola and L. josserandii. Chlorohyllum molybdites is a large, scaly-capped, green-spored species (at maturity), that prefers grassy areas and warm climes. It is known to cause strong G.I. upsets. Lepiota helveola and L. josserandii are small squamulose species that are reported to contain the same toxins as the Death Cap, Amanita phalloides. Both require a microscope to be identified.