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Description type:Original description 
Description:Pileus 28mm, convex then plano-convex but slightly and shallowly depressed at centre, not involute, pectinate-striate at margin, strongly striate to 2/3rds, brownish biege to pale ochraceous grey, darker along the radial ridges and then even hazel colour, slightly viscid when fresh, radially fibrillose-wrinkled but not disrupting to form ?akes or squamules. Fig 2A; stipe 18 x 7mm, whitish, ?ushed with colour of pileus in smudges below annulus, cylindric, equal, with obtuse abrupt rounded base slightly depressed at point of attachment to the substratum, darkening at very base; annulus about 1mm thick with a lower zone concolorous with pileus and an upper white zone, membranous, loosening, discrete; lamellae adnate to adnexed, concolorous with stipe, cream-colour, relatively widely spaced, very few intermediates but some major lamellae venose at their base. Fig 2B; context very thin; taste slightly acrid; odour slightly fruity.Basidiospores heterotropic orthotropic, white to very pale cream-colour in mass
(A - B), 8 - 9 x 6 - 7 µm excl. ornamentation, subglobose to broadly ellipsoid with aFig. 1. R. siamensis holotype. A. Macrocystidium. B. Cheilocystidia. C. Range of apices of cheilocystidia. D. Basidium. E. Terminal elements of pileipellis. F. Basidiospores.
Bars: A-E = 10 µm; F = 5 µm. slight suprahilar applanation, but lacking distinct plage, hyaline, with strongly amyloid ornamentation consisting of isolated or almost isolated conical warts 0.5-1µm high, neither catenulate nor reticulate, hilar appendage distinct < 2µm long with a basal slightly amyloid cu?. Figs. 1F & 2D; b/w photos; cheilocystidia crowded forming an almost completely homogeneous margin, 29 - 48 x (5.6-) 6.7 - 11 µm, hyaline, elongateclavate, some drawn out into broad lanceolate apex or clavate with minute apical papilla, changing to either yellowish sepia in SV or where more deeply seated dark purple-brown. Figs. 1B, C & 2C; macrocystidia widespread, hyaline with or without granular contents in ammoniacal solutions, similar to cheilocystidia but more distinct, more elongate-clavate and appendages at apex more elaborate, often drawn out intoelongate papilla, dark purple-brown in SV with granular contents. Figs. 1A, 2C&D; basidia 4-spored, narrowly clavate, in upper part with parallel sides, hyaline, with granular contents especially in SV, 30 - 38 x 6.5 - 8.5 (- 10) µm; sterigmata distinct 2- 4 µm long. Figs. 1D & 2D; pileipellis ixodermic with upper gelatinized zone 15 µm thick, suprapellis composed of radially arranged hyphae 4.5 - 6.5 µm broad with shiny walls and aggregated in places to give yellowish brown skeins intermixed with broader elements 13µm plus broad and with some rounded sphaerocytes 20 - 35 µm broad exposed between the skeins; yellowish brown, granular contents in SV in many hyphae but apparently randomly distributed over the pileus except where concentrated in the skeins of hyphae; no prominent dermatocystidia seen, replaced by poorly differentiated obtuse or torpedo-shaped terminal elements 17 - 20 (- 60) x 6.5 -11 µm or mixture of broader elements, generally with granular yellowish sepia contents in SV. Fig. 1E; stipitipellis with poorly developed, ?lamentous, terminal elements, dark purple-brown in SV, seated on hyaline, more-or-less parallel or intertwined, filamentous hyphae 2.5 -3.5 µm broad; similar in structure to parts of the pileipellis but less organized; clamp connections absent.
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