Pileus 40-80 x 30-60 mm when still closed, subglobose, ellipsoid or ovoid, expanding to campanulate or somewhat conical and then up to 100 mm wide, at first grey-brown or grey, adpressed squamulose at centre only or almost smooth. Lamellae, L = > 50, l = 3-7, first white, then greyish-brown to black. Stipe 70-150 x 8-15 mm, white; base clavate or globose, often slightly marginate.
  Spores 6.4-10.6 x 4.2-6.3 µm, Q = 1.40-1.95, av. Q = 1.50-1.75, av. L =7.9-9.3 µm, av. B = 4.6-5.9 µm, ellipsoid or ovoid, with rounded base and apex, dark red-brown; germ pore central, 1.1-1.2 µm wide. Basidia 14-32 x 8-10 µm, 4-spored, surrounded by 3-6 pseudoparaphyses. Pleurocystidia 60-210 x 30-40(-55) µm, rather narrowly cylindric or slightly utriform. Cheilocystidia 50-180 x 17-35 µm, similar to pleurocystidia. Elements of veil 50-100 x 2-8(-10) µm, branched and partly slightly diverticulate, hyphoid. Clamp-connections present.

Habitat & distribution

  On stumps of trees, sometimes seemingly terrestrial, fasciculate. Europe, America, Asia. Very common.

Remarks

  Coprinus acuminatus differs from C. atramentarius in an ochre-brown colour, a more conical shape of the usually smaller basidiocarps and somewhat narrower spores. The nearest C. romagnesianus differs in the orange-brown colour and the more abundant squamulose veil.