awns

An awn is a slender, elongated appendage that extends from a seed or fruit, most commonly found on grasses (Poaceae) but also present in some other plant groups. Awns arise from the floret components, often from the lemma or glume, and can occur as a single structure or as multiple awns on a single spikelet. Their length varies widely, from a few millimeters to several centimeters.

Awns vary in form and structure. They may be straight, curved, or bent at a knee-like angle (geniculate). Some awns are hollow or finely bristled, and many possess specialized tissues that respond to environmental cues. In some species, awns are hygroscopic, twisting or bending in response to changes in humidity or temperature, which can aid in seed placement and germination. Awns can also assist in seed dispersal by catching the wind, attaching to animal fur, or helping seeds anchor in soil after burial.

Functions of awns are diverse and context-dependent. They can enhance seed dispersal by wind or by contact with animals, and in some grasses they facilitate self-burial or drilling of the seed into the soil through hygroscopic movement. Awns may influence seed germination timing and seedling success by modulating how deeply seeds are planted. In addition, awn presence and length are useful characters in grass taxonomy and field identification.

In agriculture, awns affect threshing and handling of cereal crops. Some cultivated varieties have reduced or removed awns to ease processing and improve palatability, while others retain long awns for ecological reasons or regional preferences. The distribution and prominence of awns thus reflect a balance between plant ecology and human cultivation practices.