Anthocarp

In the four o'clock family (Nyctaginaceae), individual apetalous flowers have a tubular, petaloid calyx that resembles a sympetalous corolla. The lower portion of the calyx tightly enwraps the one-seeded achene and is persistent around the fruit as an anthocarp. The calyx base plus the enclosed seed-bearing achene is the unit of dispersal. In some members of the Nyctaginaceae, the persistent calyx base bears sticky glandular projections that aid in dispersal by adhering to the bodies of animals. This is especially true in pisonia trees (Pisonia umbellifera) in which the numerous glutinous anthocarps stick to the feathers of seabirds. This is an effective method of dispersal to distant atolls and islands of the South Pacific region. Sometimes a hapless seabird is completely covered by clusters of the sticky anthocarps, to the point where flight is difficult or impossible. Unable to remove the water-resistant, glue-like anthocarps from its feathers, the seabird drowns in the surf and is consumed by ravenous beach crabs.