Summary:
Hohenbuehelia unguicularis "can be recognized by its dark, cupulate to flabelliform fruitbodies with pale tomentum on the rear portion or apex, which may be drawn out into a pseudostipe, and by its lamellae that are silvery or pale tan when young and become dark in age. The peculiar clavate metuloids, which are brown in their lower portions and hyaline and thin-walled at their apices, are diagnostic.", (Thorn(2)). Thorn comments, "It is important to point out that Hohenbuehelia unguicularis (Fr.) Miller in this paper is based on Pleurotus unguicularis sensu Lange (1937), whereas H. unguicularis (Fr.) Miller (in Miller, in press) is based on P. unguicularis sensu Coker (1944), which is H. pinacearum" (that grows on conifers), (Thorn(5) with Latin names italicized). The dark gills in the Watling(2) description may suggest H. pinacearum and he describes it as growing on a twig of pine.

Cap:
up to 0.6cm across, cupulate [cup-shaped] or conchate [shell-shaped], pendent from an eccentric dorsal or lateral pseudostem; when dry, silver gray to brownish black or black, when revived margin becomes medium warm brown or slightly olive brown, "faintly striate in some"; bald only where weathered, otherwise white pruinose to finely tomentose, becoming densely strigose over pseudostem with white to buffy hairs, (Thorn(5)), when dry silver gray to brownish black or black, margin medium warm brown or slightly olive-brown (as revived); faintly striate in some, disc pruinose to densely strigose with white to buffy hairs, bald only where weathered, (Thorn(2)), 0.5-2.5cm across, at first obliquely cupulate, then hoof-shaped; dark fuscous sepia, white pruinose at base; bald or rugose [wrinkled] to fibrillose, (Hansen, L.)

Gills:
radiating from a point on underside, subdistant, moderately narrow; pinkish gray when fresh, gray-brown to black when dry, finely frosted under 10X; margin entire, (Thorn(5)), gelatinous, rather broad and distant; white, later grayish brown, (Hansen, L.)

Stem:
eccentric dorsal or lateral pseudostem (Thorn(2)), pseudostem distinct, farinose, (Hansen, L.)

Microscopic spores:
spores (5.0)6.0-8.5(9.0) x (2.8)3.0-4.0(4.5) microns, narrowly elliptic-phaseoliform [elliptic-bean-shaped], smooth, inamyloid, colorless; basidia 4-spored, (22)25-32 x 5.5-7.5 microns, "clavate, with dark brown sap that does not always extend to apices, leaving them hyaline"; metuloids 20-77(90) x 6-12(15) microns, "clavate or fusoid with rounded, often collapsing apices", dark brown and with walls thickened to 1.5 microns from base to middle, thin-walled and colorless at apex, scarcely projecting, but with conic cap of colorless or yellowish crystalline material 8-12 microns in diameter (looking down on hymenium), walls of metuloids deep purple in cresyl blue; cheilocystidia 22-37(60) x 4-8 microns, clavate or fusoid-ventricose, with 1 or 2 hour-glass cells 5-9 x 2.5-4 microns [as appendages], mucoid balls 4-6 microns in diameter [on tips of hourglass appendages], sometimes coalescing over gill edge, or occasionally the cystidia with 1 or 2 cylindric projections at tip up to 40 microns long and 1.0-1.5 microns wide; hymenium 24-35 microns thick, medium to dark brown in KOH, with dark flecks of metuloid bases; subhymenium 10-15(40) microns thick, subhyaline and barely distinct to dark brown; gill trama pale brown, parallel-interwoven, of hyphae 3-5 microns wide; trama 100-530 microns thick, pale brown in KOH, "darkest at upper edge adjacent to gelatinous zone, where hyphae are parallel or near so", "tangled below and descending into gills", hyphae 3-6 microns wide, with thin, or thickened, gelatinized walls; gelatinous zone often the majority of the trama, subhyaline, with pale brown and colorless hyphae tangled and ascendant below, 1.5-3.5 microns wide, smooth, "becoming repent, deeper brown and finely encrusted toward the cuticle", 2-6 microns wide; cap cuticle 10-25 microns thick, pale to dark brown in KOH, densely tangled, of pigment-encrusted hyphae 2-6 microns wide, with clamp connections; epicutis of colorless or golden brown, smooth, wavy hyphae up to 200 microns tall and 2-5 microns wide, occasionally inflated to 12 microns wide, with scattered terminal hourglass cells 7-9 x 2.5-3.0 microns, (Thorn(5)), metuloids 20-60 x 6-10 microns, (Thorn(2)), spores 7.5-8 x 3.5-4.5 microns, cylindric to allantoid, (Hansen, L.)

Spore deposit:
white (Thorn(5))

Notes:
Hohenbuehelia unguicularis is known from northern and western Europe, and northern North America. Collections were examined from MB, NS, ON, PQ, YT, and NY, (Thorn(2)). Distribution includes Denmark, Finland, Norway, and Sweden, (Hansen, L.). It was described from Sweden and reported from Denmark, France, Finland, and Russia, (Thorn(5)). There are collections at Pacific Forestry Center identified by G. Thorn for YT and by S. Redhead for BC.

EDIBILITY

Synonyms and Alternate Names:
Pleurotus unguicularis (Fr.) Kummer