achene

An achene is a type of simple dry fruit produced by many flowering plants. It is indehiscent, meaning it does not split open to release its seed at maturity, and it typically contains a single seed. In an achene, the seed is not fused to the pericarp (the wall that surrounds the seed); the pericarp forms the outer wall and remains separate from the seed as the fruit dries. Depending on the species, the pericarp can be thin and papery or thicker and tougher, but it does not become part of the seed itself.

Common examples include sunflowers and many members of the Asteraceae, where the fruit is an achene often equipped with a pappus that aids wind dispersal. In some fruits, structures such as a pappus, wing, or beak facilitate dispersal by wind or animals. The small brown grains on the surface of a strawberry, for instance, are true achenes, each containing a single seed, while the fleshy part of the strawberry is not the achene.

Achenes differ from other types of fruits in several ways. They are distinct from nuts, which generally have a hard, woody pericarp that tightly encases the seed; from caryopses (grains) in which the seed coat is fused to the pericarp, as in grasses; and from true drupes, which have a fleshy outer portion surrounding a hard endocarp. The term is widely used in plant anatomy and helps distinguish a particular mode of seed-bearing fruiting in many plant groups.

Distribution and significance vary by family, but achenes are particularly common in the Asteraceae and Ranunculaceae and play a key role in the dispersal strategies of many species.