Hohenbuehelia nigra

A species transferred in 2018 to the genus Resupinatus—a decision I personally found incomprehensible given its typical Hohenbuehelia microscopy—now returned to its former name; with a shell-shaped pileus attached dorsally, sessile, stemless, 5 to 12 mm in diameter; lamellae dark bluish grey; flesh scarce, gelatinous, without distinct odor and with a rancid taste.

Cuticle composed of filamentous hyphae, with a gelatinous layer of interwoven hyphae 1.5 to 3 µm thick separated by gelification; beneath these, more compacted hyphae 3 to 5 µm thick with greyish-brown intracellular pigment; septate and clamped in both layers.

Cheilocystidia and pleurocystidia metuloid, abundant, fusiform to lageniform, thick-walled (walls 1 to 3 µm thick), reddish brown, 30 to 75 µm long, 6 to 12 µm wide, covered over their upper two-thirds with numerous crystals, intermixed with scattered leptocystidia with an elongated neck.

Basidia clavate, 25 to 35 µm long, 6 to 8 µm wide, with sterigmata up to 5 µm, basal clamp connections and four-spored.

Spores ellipsoidal, smooth, hyaline, thin-walled, 6.5 to 9 µm long, 3.5 to 5 µm wide, with an eccentric apiculus at one end, containing oil droplets of varying size inside, and inamyloid in Melzer's reagent.