Coprinus comatus is a large, distinctive inky cap recognised by its elongate, cylindrical cap densely covered in shaggy, upturned white scales over a pale to brownish centre. As it matures, the cap expands, the gills turn pink to black, and the entire cap deliquesces into an inky fluid.

Cap: 50-150 mm tall, cylindrical when young, later bell-shaped; white with shaggy scales, centre often ochraceous to brown.
Gills: Free, crowded; white to pink to black, then liquefying from the margin upward.
Stipe: 100-300 mm long, slender, hollow, white; movable ring present but often sliding or disappearing with age.
Flesh: Soft, thin, white; rapidly deteriorates as deliquescence begins.