Pileus up to 40 x 25 mm when still closed, up to 45(-60) mm wide when mature, but never fully expanded; young pileus at first ellipsoid, ovoid, broadly cylindrical, then paraboloid, obtusely conical or campanulate with rounded umbo, finally subumbonate, completely covered with white veil when young, later splitting up in small, white or cream (Mu. 10 YR 8/2; K. & W. 4A2) felty patches, dirty yellow at centre (Mu. 10 YR 7/4, 7/6; K. & W. 5B3, 5B4); pileus below veil greyish to ochraceous, in particular at centre ochre-brown, paler towards margin (from centre to margin: Mu. 10 YR 6/3, 5/2, 6/2, 7/2, 8/2; K. & W. 5C3, 5D3, 5C2, 5B2, 5A2); primordia often cream coloured (Mu. 10 YR 7/6; K. & W. 5B4). Lamellae, L = more than 60, l = 3-5(-7), very crowded, free, first white, then grey-brown to dark brown, finally black. Stipe up to 120 x 4-10 µm, cylindrical, hollow, whitish, slightly yellowish (Mu. 10 YR 7/4, 8/4; K. & W. 5B3, 5D/E5) in the middle, somewhat fibrous with scattered velar remnants; base equal or slightly enlarged with mycelium remnants, finally and fleetingly hairy; stipe develops from orange-brown to dark brown rhizomorphs, 20-30 cm in length and up to 3 mm thick, densely available in upper 10 cm of bottom between and adherent to wooden remnants. Yellow-brown drops often are present on fresh specimens. Smell fungoid but rhizomorphs with strong smell of truffle or mould.
  Spores [140,7,4] 6.9-8.9 x 4.7-6.0 x c. 4.5-5.2 µm, ovoid or ellipsoid with rounded apex, dark red-brown, with central, 1-1.3 µm wide germ pore; Q = 1.35-1.70, av. Q = 1.50-1.55; av. L = 7.7-8.2, av. B = 5.1-5.6 µm. Basidia 13-32 x 6-9 µm, 4-spored, surrounded by 3-5 pseudoparaphyses. Pleurocystidia 70-180 x 24-50 µm, ellipsoid, oblong, sublageniform or utriform. Cheilocystidia 40-170 x 15-40 µm, to a large extent utriform and then often with rather long neck (sublageniform), ellipsoid, oblong or fusiform. Elements of veil thin-walled, branched, weakly diverticulate, 50-100 x (2-)4-9(-14) µm wide, in part slightly thick-walled (less than 0.5 µm ) and pale yellowish incrusted. Clamp-connections present.

Habitat & distribution

  Fasciculate on wood or woody remnants of broad-leaved trees, often dozens of basidiocarps together. Very rare. Europe, Japan. Occurs from May to July.

Remarks

  Coprinus strossmayeri is recognizable in the field by the rather large basidiocarps growing in clumps like C. atramentarius but in contrast to that almost smooth species the young specimens of C. strossmayeri are covered with thick, white veil breaking up in small, felty scales when pileus expands. These scales are somewhat larger than the flocculose scales of species in subsect. Domestici (sect. Micacei) and more persistent. The basidiocarps of C. strossmayeri are more slender and more conical when mature. The base of the stipe in C. strossmayeri is connected to dense, dark orange-brown rhizomorphs with strong smell of mould. Microscopically C. strossmayeri is distinguished from species in subsect. Domestici in having diverticulate velar hyphae and distinct ovoid spores (in subsect. Domestici the elements of veil are in chains, globose in great part, never diverticulate and the spores are cylindrical-ellipsoid or ellipsoid).