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Description type:Original description 
Description:Pileus 5-18 mm diam, hemispherical to campanulate or broadly convex with an acute papilla; margin sulcate to plicate; surface dull, dry, pruinose; olive brown (4F8) with darker disc when young, in age becoming olive (2F7-8) overall. Lamellae adnate, subdistant (12-16) with 0-1 series of lamellulae, not intervenose, light yellow (4A2-3) with olive brown edge. Stipe 35-56 x 0.5 mm, central, terete, cylindrical, equal, dry, dull, glabrous, non-insititious, yellowish white (4A2) at the apex, dark brown at the base, with strigose brownish orange (6C8) to light brown (6D7-8) mycelium. Odor not distinctive.
Basidiospores 11-14 (-15) x 4-5.5 (-6) µm [xmr = 12.3-13.1 x 4.6-5.3 µm, xmm = 12.7 ± 0.6 x 5 ± 0.5 µm, Q = 1.9-3.5, Qmr = 1.9-2.8, Qmm = 2.6 ± 0.4, n = 25 spores per 2 specimens], ellipsoid to clavate, smooth, hyaline, inamyloid, thin-walled. Basidia 30-38 x 6-8 µm, clavate, 4-spored. Basidioles 30-40 x 6-9 µm, fusoid to clavate. Cheilocystidia numerous, composed of Siccus-type broom cells; main body (12-) 15-23 (-27) x (4-) 5-8 (-10) µm, cylindrical to clavate or broadly clavate, rarely lobed, light yellow, inamyloid, thin- to thick-walled; apical setulae (3-) 4-7 x 0.5-1 (-1.5) µm, crowded, narrowly cylindrical to conical, obtuse to subacute, rarely forked, yellow, inamyloid, thin-walled. Pleurocystidia absent. Pileipellis strongly mottled, composed of a hymeniform layer of Siccus-type broom cells; main body (8-) 10-26 (-33) x (4-) 5-9 (-12) µm, cylindrical to clavate, broadly clavate or irregular in outline, often lobed, light yellow, inamyloid, thick-walled; apical setulae 5-9 (-10) x 0.5-1 µm, cylindrical to conical, rarely forked, subacute, light yellow to brownish yellow or golden brown, inamyloid to weakly dextrinoid, thin- to thick-walled. Pileus trama interwoven; hyphae 5-9 µm diam, cylindrical, hyaline, strongly dextrinoid, thin-walled, non-gelatinous. Lamellar trama regular; hyphae 4-10 µm diam, cylindrical, hyaline, dextrinoid, thin-walled, non-gelatinous. Stipe tissue monomitic; cortical hyphae 3-5 µm diam, parallel, cylindrical, smooth, yellowish brown (apex) to brown (base), inamyloid to weakly dextrinoid, thick-walled, non-gelatinous; medullary hyphae 6-9 µm, parallel, cylindrical, smooth, hyaline, strongly dextrinoid, thick-walled, non-gelatinous. Caulocystidia absent. Clamp connections present.
Habit, habitat and known distribution: gregarious on undetermined dicotyledonous leaves and twigs. Malaysia (Selangor).
Material examined: Malaysia, Selangor, Selayang, Kanching Forest Reserve, 9 Jan. 2005, Yee-Shin Tan, TYS 426 (Holotype: KLU-M#90; Isotype: SFSU); same location, 9 Jan. 2005, Dennis Desjardin, TYS 424 (KLU-M#91, SFSU).
Etymology: olivascens (Latin) = becoming olive coloured, referring to the pigmentation of the pileus
 
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