Coprinus sterquilinus, the midden ink cap, is a species of fungus in the family Agaricaceae.

It is white, flocculous and fibrillose when young, becoming more scaly with a creamy centre as it matures.

The stipe or stem is slender, 80 to 150 millimetres (3 to 6 in) tall, with a moveable ring just above the slightly bulbous base.

Both share the characteristic of the genus to autodigest; starting at the base of the gills, the spores develop and discharge, and the discharged basidia and the supporting hyphae produce enzymes which dissolve the tissues, and these drip from the base of the gills as a black liquid (which can be used as ink).

In an experiment, one fruit body lifted 204 g (7.2 oz), giving an upward pressure of the stipe of two thirds of an atmosphere.