Pileus 40-70 x 20-50 mm when still closed, subglobose, ellipsoid or ovoid, expanding to conical and then up to 100 mm wide, at first white and silvery fibrillose from veil, then greyish to grey with pale brown, dirty ochraceous centre. Lamellae, L = > 50, l = 3-7, first white, then greyish-brown to black. Stipe 80-150 x 7-15 mm, white; base clavate and white tomentose.
  Spores 11.1-14.4 x 6.7-8.3 µm, Q = 1.50-1.95, av. Q = 1.70, av. L = 12.3-12.5 µm, av. B = 7.3-7.4 µm, amygdaloid, warty, with rounded to slightly conical base and apical papilla, very dark red-brown; germ pore narrow, c. 1 µm wide. Basidia 25-42 x 8-10 µm, 4-spored, surrounded by 3-6 pseudoparaphyses. Pleurocystidia 80-180 x 35-50 µm, utriform to subcylindric. Cheilocystidia 50-160 x 30-60 µm. Elements of veil 20-125 x 7-14 µm, hyphoid. Clamp-connections present.

Habitat & distribution

  On stumps of broad-leaved trees, sometimes on the ground, fasciculate, very rare. Known from Europe and America.

Remarks

  Coprinus insignis is easily to determ by the hyphoid veil, the warty, amygdaloid spores and the medium-sized, fasciculate growing basidiocarps.