Holotypus: Hawai`i, Hawai`i, 26 May 1993, D. E. Desjardin 5720 (SFSU).
Isotypus: BISH.
Etymology. ohia = associated with ohi`a, the Hawaiian name for Metrosideros polymorpha.
Pileus 8-10 mm diam, convex when young, plano-convex at maturity, striatulate; surface dry, dull, hygrophanous, suede-like to subfibrillose overall, brownish orange (6C-D5-6). Context thin, concolorous with pileus surface. Odor and taste not distinctive. Lamellae shallowly adnexed, subdistant with a few scattered lamellulae, broad (-2 mm), convex, pale brownish orange (6B5-6). Stipe 10-15 X 0.5 mm, central, terete, equal, hollow; apex pruinose, glabrous elsewhere; surface brownish orange (6C-D5-6); base not appreciably darkened; partial veil absent.
Basidiospores 11.0-13.5(-14.0) X (5.0-)5.5-6.5 µm [mean = 12.4 ± 0.8 X 6.0 ± 0.4 µm, Q = 1.9-2.4, Q mean = 2.1 ± 0.1, n = 25], amygdaliform, often with a suprahilar flattening or shallow depression, rusty brown, with or without a distal callus, verrucose near proximal end and along rim of plage, otherwise weakly roughened, with a distinct smooth plage; perispore present with scattered blisters; germ pore absent. Basidia (20-)22-28 X 8.5-10.5 µm, clavate, 4-spored. Basidioles clavate. Lamellar edge sterile; cheilocystidia numerous, 25-47 X 5-10 µm (at broadest), tibiiform, rarely ventricose-rostrate or narrowly lageniform; capitulum 5.5-9.0 µm diam with neck 3.0-4.5 µm diam, hyaline, thin-walled. Pleurocystidia absent. Pileipellis a cutis with scattered pilocystidia; hyphae 4-16 µm diam, radially arranged, loosely interwoven, cylindric to slightly inflated, incrusted with granular-roughened or annular tawny pigments; walls thin, nongelatinous, inamyloid, hyaline to pale yellowish orange; pilocystidia only slightly differentiated from subtending hyphae, 40-60 X 8-16 µm, cylindric to clavate, often subcapitate, smooth or weakly incrusted, thin-walled, hyaline or with pale yellowish orange plasmatic pigment. Tramal hyphae interwoven, 4-30 µm diam, cylindric to inflated, nonincrusted, nongelatinous, thin-walled, hyaline to pale yellowish orange, few with brownish orange contents. Stipe tissue monomitic; cortical hyphae 3-8 µm diam, parallel, cylindric, nongelatinous, with hyaline to pale yellow granular incrustations; medullary hyphae similar but smooth and up to 16 µm diam. Caulocystidia numerous, solitary to clustered on stipe apex, absent elsewhere, 44-88 X 4-8(-10) µm, cylindric, flexuous, seldom ventricose or with a slightly enlarged base, non-capitate; apex obtuse, hyaline, thin-walled. Clamp connections present but not at all septa.
Habit, habitat and distribution. Solitary among mosses on very rotten ohi`a (Metrosideros polymorpha; Myrtaceae) logs in Montane Wet Ohi`a Forest. May. Hawai`i. Known from only the type locality.
Specimen Examined. U.S.A. HAWAII: Hawai`i, Saddle Rd. at 18.5 mi kipuka, 26 May 1993, D. E. Hemmes (DED 5720) (HOLOTYPE, SFSU; ISOTYPE, BISH).
Commentary. Galerina ohiarum is characterized by the following combination of features: small basidiomata with suede-like pileus reminiscent of Tubaria in the field; lack of a partial veil; relatively large, weakly roughened amygdaliform basidiospores; tetrasporic basidia; tibiiform cheilocystidia; distinctive cylindric-subcapitate pilocystidia and cylindric-flexuous caulocystidia; and habit among mosses on rotten logs of ohi`a in native montane forests. The basidiospores and cheilocystidia of G. ohiarum are reminiscent of several species, including the European G. mycenoides (Fr.) Kühner (1935), G. tsugae A. H. Smith & Singer (1955) from North America, and G. dominici Singer in Smith & Singer (1964) from Venezuela. Galerina mycenoides differs in forming velate basidiomata, the pileus is glabrous, lacking pilocystidia, the basidia are bisporic, and basidiomata form on rotting mosses in bogs. Galerina tsugae differs also in forming velate basidiomata with a glabrous pileus that lacks pilocystidia, and in forming nearly smooth basidiospores, only subcapitate or noncapitate cheilocystidia, and in fructification on hemlock logs (holotype, MICH!). Basidiospores of Galerina dominici are shorter (9-11 µm) and subellipsoid, caulocystidia are often subcapitate, and there are no pilocystidia (holotype, LIL!). Galerina ohiarum is apparently restricted to montane native forests and is considered by us to represent a native, possibly endemic, species.