Cap ellipsoid to bullet-shaped in youth, 4-7 mm tall x 2-3 mm wide, becoming obtuse-conic to convex, then plane, 7 to 12 mm expanded; margin at first incurved, then decurved, revolute in age; surface plicate-striate, covered with whitish granules which become pale-yellow and coarser at the disc; cap becoming ash-grey overall as the gills mature; context membranous, watery-grey, deliquescing in age; odor and taste mild.
Gills free, close, relatively narrow, 18-30 reaching the stipe, whitish, then grey, finally blackish, especially the edges; lamelullae in up to three-series.
Stipe 2.5-5.0 cm long, 0.5-1.0 mm thick, equal except enlarged at the base and apex, fragile, tubular, hollow; surface glabrous to inconspicuously longitudinally striate (use hand lens), translucent-white; partial veil floccose-membranous, leaving a small, erect, fringed annulus medial or high on the stipe.
Spores 6.0-8.5 x 5.5-7.0 x 4.5-5.5 µm, subglobose to apple-shaped, or weakly pentagonal in face-view, elliptical in profile, smooth, germ pore central, dark-brown when mounted in water; spore print black.
Solitary to clustered on horse and cow dung; fruiting throughout the year after moist periods; inconspicuous, occasionally common.
Edibility unknown, insignificant.
Coprinopsis ephemeroides is a small dung-dwelling species recognized by a whitish, plicate-striate cap covered with cream-colored granules, yellowish at the disc. The presence of an annulus and creamy-yellow disc are important fieldmarks that help to separate it from the very similar Coprinus cordisporus. The latter, which often fruits with C. ephemeroides, lacks a ring, and has cap granules that tend to be tan to cinnamon-brown. Two additional species should be mentioned, Coprinus patouillardii and Coprinus cardiasporus. The former is regarded by some authors as conspecific with C. cordisporus, but may differ in slightly larger size, substrate preference (plant matter rather than dung), along with subtle microscopic differences. Coprinus cardiasporus, a name confusingly similar to C. cordisporus is also a small, dung dwelling species with a granulose cap. It is differentiated largely on microscopic grounds, the most obvious one being the spores which although heart-shaped in face-view are not angular or pentagonal as in the other species.