achene

Dry, one-seeded fruit that develops from a single ovary and does not split open to disperse the seed. Achenes commonly occur in groups - for example, the fruiting heads of buttercup Ranunculus and clematis. The outer surface may be smooth, spiny, ribbed, or tuberculate, depending on the species.

An achene with part of the fruit wall extended to form a membranous wing is called a samara; an example is the pendulous fruit of the elm Ulmus. During the development of a caryopsis, the carpel wall becomes fused to the seed coat; this type of fruit is typical of grasses and cereals. A cypsela is derived from an inferior ovary and is characteristic of the daisy family (Compositae). It often has a pappus of hairs attached, which aids its dispersal by the wind, as in the dandelion.