A small dark greyish brown to black oyster fungus, with a well-developed stem fruiting on sand dunes near the base of Ammophila arenaria (marram grass). In GB, the name Hohenbuehelia culmicola has been used for both H. culmicola s.s. and H. bonii (raised to species level in 2016), which is a larger, brownish and barely stalked species with the same or similar habitat preferences.
Pileus (cap) (5)10-24(40) mm diam., flattened to convex and shallowly depressed from side, circular, flabelliform (fan-shaped), spatula shaped or kidney shaped from above, blackish brown, more dark brown towards margin, tomentose (with matted "hairs") all over. Lamellae (gills) crowded, subdecurrent to decurrent (extending down stalk), narrow, greyish white to light ochre, sometimes slightly brown or blackish grey. Stipe (stalk) 2-10(20) x 1.5-6(10) mm, concolorous with pileus, eccentric (offset) or lateral (from side), cylindrical, solid, slightly leathery, covered in whitish tomentum or velutinous (with matted or dense silky "hairs"). Spores 9.0-11.0 x 5.0-6.0, Q 1.6-1.9, ellipsoid to oblong, no Melzer’s reaction. Basidia 22-40 x 7-11 µm, 4-spored, clavate, clamped. Spore print white. Metuloid pleurocystidia fusiform with acuminate apex (tapering to a point), variably with a thick crystalline apical encrustation, 35-95 x 5-18 µm, wall thickness 1.5-3.5 µm, colourless or yellowish to blackish grey. Cheilocystidia (cystidia on edge of gills) 15-44 (51) x 5.5-10(25) µm, numerous, clavate (club-shaped) and rostrate (beak-shaped) or fusiform (tapering at both ends) and rostrate with 1-5 very short rostra, colourless or yellowish, opaque from granular contents, thin-walled; capitulum strangulated or obpyriform (inversely pear-shaped). Pleurocystidia (cystidia on gill surface) rare, similar to cheilocystidia. Pileipellis (upper cap layer) a trichoderm (outermost hyphae like hairs) consisting of a superior tomentum, made up of interwoven, colourless, smooth, gelatinous, cylindrical hyphae, 2.0-3.5 µm in diameter, and an inferior layer, 7-23 µm thick, of interwoven, thin-walled, gelatinous, dark brown incrusted hyphae, 2.0-4.0 µm in diameter.
Description adapted from Elbourne, S. A. (1995). Hohenbuehelia. In C. Bas, Kuyper, TH. W., Noorderloos, M.E. & Vellinga, E.C. (Ed.), Flora Agaricina Neederlandica (Vol. 3, pp. 158-166). Rotterdam: A. A. Balkema.