Awn (botany)

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Wild rye ear with awns

In botany, an awn is either a hair- or bristle-like appendage on a larger structure, or in the case of the Asteraceae, a stiff needle-like element of the pappus.

Awns are characteristic of many grasses (Poaceae), where they extend from the lemmas of the florets. This often makes the hairy appearance of the grass synfloresce. Awns may be long (several centimeters) or short, straight or curved, single or multiple per floret. Some genera are named after their awns, such as the three-awns (Aristida).

In some species, the awns can contribute significantly to photosynthesis, as, for example, in barley.

The awns of wild emmer wheat spikelets effectively self-cultivate by propelling themselves mechanically into soils. During a period of increased humidity during the night, the awns of the spikelet become erect and draw together, and in the process push the grain into the soil. During the daytime the humidity drops and the awns slacken back again; however, fine silica hairs on the awns act as ratchet hooks in the soil and prevent the spikelets from reversing back out again. During the course of alternating stages of daytime and nighttime humidity, the awns' pumping movements, which resemble a swimming frog kick, drill the spikelet as much as an inch into the soil.[1]

References[edit]

  1. ^ Elbaum, Rivka; Zaltzman, Liron; Burgert, Ingo; Fratzl, Peter (2007). "The Role of Wheat Awns in the Seed Dispersal Unit". Science 316 (5826): 884–886. doi:10.1126/science.1140097. PMID 17495170. 

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