Panaeolus rickenii

A coprophilous species growing on heavily nitrogenous ground or directly on dung, with a parabolic pileus featuring a prominent umbo, 1 to 2.5 cm across, brown, ascending adnate blackish lamellae, and a cylindrical, hollow, dark brown stipe coated in whitish pruina.

Pileipellis composed of a hymeniderm of globose to pyriform thin-walled cells 15 to 28 µm in diameter, containing abundant brown intracellular pigment.

Caulocystidia present, particularly at the stipe apex, clustered in bundles, irregular, cylindrical, sinuous, with rounded apices.

Cheilocystidia subcylindrical to lageniform, flexuous, 25 to 35 µm long, 7 to 10 µm wide at the base, terminating in an elongated neck.

Pleurocystidia absent.

Basidia cylindrical-clavate, 20 to 25 µm long, 10 to 14 µm wide, partly clamped, 4-spored.

Spores lentiform to citriform, smooth-walled, brown under the microscope, 10 to 14 µm long, 7.5 to 11 µm wide, with an apiculus at one end and a conspicuous germ pore at the opposite end.

Microscopically practically identical to Panaeolus acuminatus and long considered synonymous; currently both maintain distinct species status based on molecular phylogeny. Macroscopically, Panaeolus rickenii has a parabolic pileus (taller than broad) and is strictly coprophilous, fruiting directly on dung, whereas Panaeolus acuminatus typically has a broader conical pileus and a nitrophilous grassy habitat.