Closed pileus globose, subglobose or ellipsoid, up to 7 mm high and 5 mm wide, completely covered with powdery, dark grey-brown veil (Mu. 10 YR 3-5/2, 7.5 YR 6-7/4), often with olive-green hue (Mu. 5 Y 3/1-2, 2.5 Y 5/4, 5 Y 5/3), forming small granular flocks at centre of pileus; veil at margin quickly disappearing, showing the white pileal surface; expanded pileus up to 12(-15) mm wide, conical or convex, later applanate. Lamellae, L = 14-24, l = 0-3, narrowly adnate, white at first then greyish to black. Stipe up to 30 x 0.5-1 mm, white, somewhat hyaline, at base clavate, up to 1.5 mm wide, often with brownish velar flocks. Smell absent.
  Spores [140,7,6] 6.3-8.9 x 3.8-5.2 µm, Q = 1.45-2.10, av. Q = 1.70-1.85, av. L = 7.3-7.9, av. B = 4.0-4.6 µm, amygdaliform or ovoid, with central germ pore, red-brown. Basidia 13-30 x 6-8 µm, 4-spored, surrounded by 4-5 pseudoparaphyses. Pleurocystidia absent. Cheilocystidia 10-28 x 8-15 µm, variably shaped, narrowly clavate, clavate, ellipsoid, broadly utriform or subglobose, sometimes with median constriction. Veil made up of (sub)globose to ellipsoid or fusiform elements, smooth to (usually) strongly granular, up to 50 µm wide. Clamp-connections present.

Habitat & distribution

  Gregarious, on and around stumps of deciduous trees. Rare in the Netherlands.

Remarks

  Coprinus coniophorus is very easy to identify, but the caespitose growth and shape of the basidiocarps (similar to Coprinus disseminatus) cause it to be easily overlooked. When in the field a group of 'Coprinus disseminatus' is encountered with rather whitish basidiocarps, it is worth-wile to have a closer look, as it may well turn out to be Coprinus coniophorus. Contrary to Coprinus disseminatus, the primordia are not cream-coloured but dark grey. Later, when the pileus is expanding, the white colour of the pileus becomes visible as the veil disappears. As pointed out in the description, young specimens of Coprinus coniophorus may have a weak olivaceous tint, which is visible only under certain circumstances. Microscopically the shape of the cheilocystidia and size and shape of the spores are important diagnostic features. Sometimes the spores are ovoid for the most part, but usually they are distinctly amygdaliform, protruding to the germ-pore. Cheilocystidia are not always easy to find, sometimes sparse,
  Coprinus poliomallus, another small mouse-grey species grows on dung, solitary or in small groups. It has always elliptical or ovate spores and distinct pleurocystidia.