Summary:
Panaeolus foenisecii is distinguished by a bluntly conic to bell-shaped young cap that is hygrophanous chestnut-brown to dark brown or cinnamon-brown, often with a darker marginal band, a thin fragile stem, absent veil, fruiting in grass, and a dark brown spore deposit. Panaeolus foenisecii had been segregated from Panaeolus into Panaeolina, because of its brown or purple brown (as opposed to black) spores that are rough. Panaeolina foenisecii (Pers.) Maire was given as the current name in the online Species Fungorum, accessed June 1, 2019. However, according to D. Miller, pers. comm., there is some DNA evidence that it nests among other Panaeolus species and does not form a separate clade. It is common in lawns (perhaps the most common lawn-inhabiting mushroom in the Pacific Northwest according to Trudell(4)).

Gills:
"adnate to adnexed or seceding, fairly close"; brown becoming deep brown, deep grayish brown, or chocolate brown, "the faces often somewhat mottled and the edges paler or whitish", (Arora), adnate, soon seceding, close, moderately broad; pallid when young, becoming dull brownish or deep brown, and becoming slightly mottled, (Stamets), broad and ventricose (Smith)

Stem:
4-8cm x 0.15-0.4cm, equal or with a widened base, fragile; "white to dingy brownish (often becoming brown from the base upward)"; more or less smooth, (Arora), 4-8cm x 0.2-0.35cm, equal, brittle; pallid to whitish, darkening from base up when old or with handling; pruinose, slightly striate and twisted toward apex, (Stamets), hollow, rigid, straight and equal or flattened or twisted-striate, base enlarged; lighter near top when young; covered with soft, short white hairs, apex striate, white mycelium at base, no veil remnants, (Menser)

Veil:
absent (Arora)

Odor:
fungoid (Smith), pleasant (Miller)

Taste:
acidulous (Smith), mild (Miller)

Microscopic spores:
spores 12-17 x 6-9 microns, elliptic, rough, (Arora), spores 12-17 x 7-9 microns, roughened; pleurocystidia present in the form of chrysocystidia, but difficult to find and generally not projecting beyond basidia, cheilocystidia 22-30(35) x 7-12 microns, "variable, fusoid-ventricose, sometimes clavate or sublageniform with a long, flexuous neck", (Stamets); spores 12-15 x 6.5-9 microns, ovate in face view, somewhat to obscurely inequilateral in side view, "ornamented with irregular low warts or areolate patches of outer wall material, apex truncate from an apical pore", spores in KOH dingy cocoa, in Melzer''s reagent about the same or duller rusty brown, wall about 0.5 microns thick; basidia 4-spored, 24-30 x 8-11 microns, clavate, projecting slightly when sporulating; pleurocystidia none, but possibly scattered pseudocystidia buried in hymenium, cheilocystidia 28-42 x 7-13 microns, fusoid-ventricose with obtuse apex, thin-walled, smooth, colorless, content not distinctive; clamp connections present, (Smith), spores 11-18 x 6-9 microns, almond-shaped, (Trudell)

Spore deposit:
deep brown or purple-brown (Arora), dark brown not black (Stamets), dark vinaceous brown (Smith)

Notes:
It has been reported specifically for BC (Redhead(5)), and material was examined from WA, OR, ON, CA, IL, MA, MD, MI, MN, MT, NY, PA, TN, WI, Mexico, (Smith). There are collections at the University of Washington from WA, OR, AK, CO, NY, and ON.

EDIBILITY

harmless in small quantities, but potentially poisonous to toddlers in lawns, since some collections contain traces of psilocybin, but western collections apparently inactive, (Arora), not active to weakly active, no psilocybin or psilocin found in a study of Pacific Northwest specimens, (Stamets)

Synonyms and Alternate Names:
Panaeolina foenisecii (Pers.) Maire
Psathyrella foenisecii (Fr.) A.H. Sm.