Summary:
Features include 1) a conic - bell-shaped cap that is dark brown or red-brown, viscid to lubricous, striate when moist, and appendiculate with fine fibrils if at all, 2) close to crowded gills that blacken with spores leaving the gill edge white, 3) a slender, pruinose stem that is dark red brown or colored as the cap, 4) growth in grassy areas and in well-manured grounds or on dung, and 5) microscopic characters. Moser distinguishes P. rickenii Hora = P. acuminatus sensu Ri., Lge., K.&R. with a cap that is bell-shaped when young, and fairly dark red-brown to chocolate-brown, a stem that is dark red-brown, and fruiting in woods and pastures, from P. acuminatus (Schaeff. ex Secr.) Quel. with a conic-pointed cap that has a dark band around the margin, the cap otherwise flesh-tawny-hazel, the lower stem black-brown, gray-brown, the upper stem pallid, and fruiting on dung. P. acuminatus (Secr.) Quel. sensu Ricken is as common in the Pacific Northwest as Panaeolus papilionaceus according to Stamets(1).

Cap:
1.5-2.5(4)cm across, conic to conic - bell-shaped becoming more bell-shaped to convex, then expanding to flat often with low umbo, margin incurved at first; hygrophanous, chestnut or deep reddish brown, fading to tawny from the apex and remaining darker along the margin; smooth, viscid to lubricous when wet, margin appendiculate with fine fibrils if at all, "shortly striate along the margin, then opaque", (Stamets), pruinose (Courtecuisse), wider than high with age, scalloped when young and translucent-striate when moist, (Menser)

Flesh:
dark (Courtecuisse), buff-brown (Buczacki)

Gills:
"adnate to adnexed to sinuate, close to crowded, broad", several tiers of subgills; very dark purplish gray-black at maturity and mottled; edge even, (Stamets), edge white-floccose (Moser)

Stem:
4.5-10.5(15)cm x 0.25-0.65cm, equal to slightly widened at base or apex; very dark reddish brown or almost colored as cap; pruinose, often with small water droplets adhering near top of stem, (Stamets), pruinose on vinaceous brown ground (Courtecuisse), apex striate, base enlarged and covered with white mycelium, (Menser)

Veil:
[none or inconspicuous]

Odor:
indistinct (Buczacki)

Taste:
indistinct (Buczacki)

Microscopic spores:
spores 11-16 x 7.5-11 microns, lemon-shaped, smooth; basidia 4-spored, rarely 2-spored; pleurocystidia absent, cheilocystidia irregular in form, (Stamets)

Spore deposit:
blackish (Stamets), purple-black (Buczacki)

Notes:
Panaeolus acuminatus has been reported specifically from BC by Lowe(1). There is a collection from BC at the University of British Columbia. There is a collection from OR at Western Washington University. At the University of Washington there are collections from WA and AK. The only two collections to specify sensu Ricken are two of the WA collections at the University of Washington.

EDIBILITY

Synonyms and Alternate Names:
Panaeolus rickenii Hora