First person to use this name on MO: Image Sharer
Etymology: proximus (Lat.), close to, next to.
Diagnosis: Pileus dark brown, disc with numerous small but conspicuous tufts of erect fibrils, context unchanging
upon exposure. Stipe covered with concolorous loose fibrils and small scales, not pruinose anywhere, stipe base olive grey, cortina evanescent. Odor not distinctive. Basidiospores ovoid-elliptical. Cheilocystidia present. Pleurocystidia and caulocystidia absent. In tropical montane forest dominated by Castanopsis in Thailand.
Pileus 20–40 mm wide, at first broadly and obtusely conical with decurved margin, becoming distinctly campanulate in age, not expanding, dark brown (6–7F6–8) overall, at disc with numerous small but conspicuous, conical and concolorous spines (formed from tufts of erect fibrils), towards margin with smaller scales and fibrils, at non-striate margin glabrous, dry, veil remnants absent; context 1–2 mm thick, watery white, unchanging upon exposure. Lamellae 28–36 reaching stipe, 7 (–15) lamellulae, adnexed, up to 5 mm wide, at first beige, becoming brown (6E6– 8), entire edges concolorous. Stipe 35–70 × 2–5 mm, central, cylindrical, ± equal, covered with concolorous, loose fibrils and scattered small scales, apex not pruinose, brown (6E5–8) above, at base olive grey, dry; cortina present in young specimens, not persisting; context solid or stuffed, with olive grey tinge in base. Odor not distinctive. Taste not recorded.
Basidiospores 8.5–10 × 5–5.5 μm, ovoid-elliptical (in side and face view), brown, smooth, germ pore absent, brown in deposit. Basidia 35–42 × 8–10 μm, 4-spored, clavate. Cheilocystidia 20–55 × 10–15 μm, polymorphic, shape ranging from clavate to broadly fusoid, thin-walled, hyaline, crystals absent. Pleurocystidia absent. Caulocystidia absent. Pileipellis a cutis of suberect or repent, cylindrical hyphae, 6–8 μm wide, terminal cells not differentiated, non-gelatinized wall hyaline, encrusted with yellow-brown pigment; subpellis hyphae cylindrical or slender subfusoid, 12–20 μm wide, wall encrusted with yellow-brown pigment; oleiferous hyphae absent. Clamp connections present.
Habitat: Singly on soil in tropical montane forest (dominated by Castanopsis), ca. 1000 m elev.
Known distribution: Northwest Thailand.
Notes: The olive grey colored context in the base of the stipe indicates that I. proxima belongs to the intricate group of species related to I. calamistrata (Fr.) Gillet, a common species complex with a wide distribution in the Northern Hemisphere (Stangl 1989, Horak 2005) which usually have a reddening context in stipe. To date this reddening of context has not been observed in I. proxima. In the Southern Hemisphere the related I. calamistratoides E. Horak (1977) is reported from New Zealand where it is frequently encountered in Nothofagus forests. Molecular results (Fig. 1; Kropp et al. 2013) support placement of I. proxima in the Inosperma clade where it is closely related to I. bongardii (Weinm.) Quél. and other members of Inocybe sect. Cervicolores. At present I. proxima is known only from the type collection.