A number of potentially poisonous mushrooms are superficially similar but do not match all the key characteristics. The less common
Coprinopsis romagnesiana differs in that the cap is covered with darker brown appressed scales and lacks granules when young. It interacts with alcohol in a similar way to
Coprinopsis atramentaria.
Coprinellus domesticus, of unknown edibility, differs in that the young cap is dotted with whitish scales and the fungus forms a mat of orange, hair-like fibers on the decaying log that it grows from. The less common
Coprinellus flocculosus, of unknown edibility, differs in that the young cap is covered with tufts of whitish, felty warts. The edible
Coprinellus disseminatus is smaller (under 2 cm broad), lacks granules on the cap, and does not become inky when old.