Psathyrella populina (Britz.) Kits van Wav.
Descriptions & illustrations. - Heim & Romagn., I.e.; Kühn. & Romagn., I.e.; Imler in Bull. trimest. Soc. mycol. Fr. 71: Atlas pl. 106. 1955; Svrcek in Cesksi Mykol. 23: 262. 1969 (as P. sylvestris, Czech); Printz in Friesia 10: 335. 1974 (as P. silvestris); A.H. Smith, I.e. (as P. lepidotoides).
Cap 17-53 mm, at first hemispherical or paraboloid, then spreading to convex, finally plane, without umbo, rarely slightly umbonate or vaguely depressed, with rounded off, obtuse, slightly irregular or torn margin, whitish, pale greyish, brown, isabelline, olivaceous, at centre beige with ochreous hue, towards margin paler and greyer with faint violaceous hue, not hygrophanous, opaque, sprinkled with adpressed dark, ± triangular, ochre, brown, brown-bistre or sepia, adpressed, very distinct small scales or bundles of fibrils, often fairly thinly spread (in places even absent) contrasting with paler or whitish ground colour, scanty towards centre, becoming fewer and much finer towards margin. Gills 2.5-6 mm broad, crowded to subdistant, roundly adnexed, segmentiform to subventricose, at first pale brown, then purplish, finally brown chocolate, with pruinose white edge. Stem 30-65 x 3-6.5 mm, usually short, cylindrical, sometimes slightly thicker towards base, straight or slightly curved, white, later towards base brownish or brownish ochre-olivaceous (always paler than cap) and very finely speckled from small brown or brown-olivaceous fibrils, remaining white at sulcate, pruinose, and satiny apex. Flesh in centre of cap fairly thick (up to 4 mm), thin at margin, not watery, very white or pinkish, in the end in stem faintly pale straw or cream coloured, smell indistinctive. Trama of 'washed' gill brownish yellow (Mu. 10 YR 6/4) or yellow (Mu. 10 YR 7/6), equally strong from base to edge. Spore print purplish brown.
Spores 6.5-8 x 4.5-5.5 µm (in profile), x 5-5.5 (in face view) (mean values 7.5-7.8 x 4.7-4.9 x 5.3 µm: 3 collections), in face view subtriangular to almost square with rounded apex and rectangular or subrectangular base, sometimes with a small bulge on one side at or near base, in profile usually phaseoliform or subphaseoliform, in water orange brown (Mu. 5 YR 5/6, 4/8; 7.5 YR 5/6), in NH4OH 10% darker (Mu. 5 YR4/6,4/4) in KOH 5% brown (Mu. 7.5 YR 4/4), not opaque, with small but distinct germ pore ± 1 µm and very small hilar appendix. Basidia 17.5-24 x 8-9.5 µm, clavate to subcylindrical, 4-spored. Pleurocystidia (35-)47.5-70 x 12.5-22.5 µm, utriform-pedicellate (some ellipsoid-pedicellate with very broad apex), numerous to abundant, rarely scarce, thin-walled, colourless, some or many faintly amyloid in Melzer, apex covered by a mucoid mass (often large) staining green in NH40H 10% in fresh material. Marginal cells: pleurocystidioid cheilocystidia 30-55 x 12.5-20 µm, sometimes mixed with a motley of large and smaller ellipsoid and clavate cells (17.5-37.5 x 9-17.5 µm) and smaller spheropedunculate and clavate cells (17.5-20 x 7.5-10 µm), sometimes mixed with practically only the latter cells; all cells thin-walled and colourless. Hymenophoral trama in NH40H 10% distinctly yellowish brown from membranal pigment, without yellow septa or encrustations. Pileipellis a 3-5 cells deep layer of colourless to very pale brown, subglobose cells, 15-30 µm diam., covered by a thick layer of cylindrical hyphae, 5-15 µm broad, densely filled with dark brown, vacuolar pigment.
Habitat & distribution. - On dead wood of Populus (according to Romagnesi also on Fagus). Very rare, found twice in the Netherlands (Oct., Nov.); reported from France (according to Romagnesi fairly common and occurring chiefly in May, but also in Oct., Nov.) and the British Isles (K).
