Awn

An awn is a slender, elongated bristle that extends from seeds or floral parts in many grasses and some other plants. In grasses, awns most commonly arise from the lemma or glumes and vary in length, stiffness, and orientation. They may be straight, twisted, or geniculate (bent with a sharp angle near the base); some species carry multiple awns on a single floret.

Awns serve several ecological roles. They can aid seed dispersal by catching wind or by clinging to fur or feathers. Many awns are hygroscopic, twisting or bending with changes in humidity to help seed burial or penetration into the soil. In addition to dispersal and burial, awns can influence germination or seedling establishment and may deter herbivory or physical damage in some species.

Awareness of awns is especially important in the grass family, Poaceae, where numerous temperate grasses and cereals exhibit awned forms. Barley (Hordeum vulgare) often has long awns, while wheat (Triticum spp.) shows considerable variation, with some cultivars bearing long awns and others being awnless. Rice (Oryza sativa) is typically awnless in cultivated varieties. The presence and length of awns are traits used in taxonomy, ecology, and crop breeding.

Human cultivation has altered awn expression in many cereals. Some modern varieties have reduced or removed awns to ease harvesting, processing, or storage, whereas other types retain prominent awns for forage value, drought tolerance, or ecological considerations.