In Asteraceae, the pappus is the modified calyx, the part of an individual floret, that surrounds the base of the corolla tube in flower. It functions as a wind-dispersal mechanism for the seeds. The term is sometimes used for similar structures in other plant families e.g. in certain genera of the Apocynaceae, although the pappus in Apocynaceae is not derived from the calyx of the flower.

In Asteraceae, the pappus may be composed of bristles (sometimes feathery), awns, scales, or may be absent, and in some species, is too small to see without magnification. In genera such as Taraxacum or Eupatorium, feathery bristles of the pappus function as a "parachute" which enables the seed to be carried by the wind. The name derives from the Ancient Greek word pappos, Latin pappus, meaning "old man", so used for a plant (assumed to be an Erigeron species) having bristles and also for the woolly, hairy seed of certain plants.

The pappus of the dandelion plays a vital role in the wind-aided dispersal of its seeds. By creating a separated vortex ring in its wake, the flight of the pappus is stabilized and more lift and drag are produced. The pappus also has the property of being able to change its morphology in the presence of moisture in various ways that aid germination. The change of shape can adjust the rate of abscission, allowing increased or decreased germination depending on the favorability of conditions.