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.
A wild rye ear (spike) with awnsAwns on the fruit of an Australian species of grass
Awns are characteristic of various plant families, including Geraniaceae and many grasses (Poaceae).
A common name for awns includes foxtails, for they tend to stick to animals passing by the plant.
Descriptionedit
In grasses, awns typically extend from the lemmas of the florets. This often makes the hairy appearance of the grass synflorescence. Awns may be long (several centimeters) or short, straight or curved, single or multiple per floret. Some biological genera are named after their awns, such as the three-awns (Aristida).
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 swimming frog kick, drill the spikelet as much as an inch into the soil.[1]
Geranium dissectum fruits, one undischarged, two of which have discharged their seed-bearing carpels by flinging out the seed as the awns dry, shrink, and split off elasticallyAwns on the carpels of Erodium moschatum that twist as they dry. They might either fling off their seed, or entangle in the coats of animals, or partly bury the seed if they land suitably on soil.
When awns occur in the Geraniaceae, they form the distal (rostral) points of the five carpels, lying parallel in the style above the ovary. Depending on the species, such awns have various seed-dispersal functions, either dispersing the seed by flinging it out (seed ejection); flinging away the entire carpel so that it snaps off (carpel projection);[2] entangling the awn or bristles on passing animals (zoochory); or possibly burying the seed by twisting as it lies on soft soil.[3]
Referencesedit
^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.
^Yeo, P. F. (1984). "Fruit-discharge-type in Geranium (Geraniaceae): its use in classification and its evolutionary implications". Botanical Journal of the Linnean Society 89: 1–36. doi: 10.1111/j.1095-8339.1984.tb00998.x
botany, other, uses, disambiguation, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, botany, news, newspapers, books. For other uses see Awn disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Awn botany news newspapers books scholar JSTOR December 2009 Learn how and when to remove this template message 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 A wild rye ear spike with awnsAwns on the fruit of an Australian species of grassAwns are characteristic of various plant families including Geraniaceae and many grasses Poaceae A common name for awns includes foxtails for they tend to stick to animals passing by the plant Description editIn grasses awns typically extend from the lemmas of the florets This often makes the hairy appearance of the grass synflorescence Awns may be long several centimeters or short straight or curved single or multiple per floret Some biological 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 swimming frog kick drill the spikelet as much as an inch into the soil 1 nbsp Geranium dissectum fruits one undischarged two of which have discharged their seed bearing carpels by flinging out the seed as the awns dry shrink and split off elastically nbsp Awns on the carpels of Erodium moschatum that twist as they dry They might either fling off their seed or entangle in the coats of animals or partly bury the seed if they land suitably on soil When awns occur in the Geraniaceae they form the distal rostral points of the five carpels lying parallel in the style above the ovary Depending on the species such awns have various seed dispersal functions either dispersing the seed by flinging it out seed ejection flinging away the entire carpel so that it snaps off carpel projection 2 entangling the awn or bristles on passing animals zoochory or possibly burying the seed by twisting as it lies on soft soil 3 References edit 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 Yeo P F 1984 Fruit discharge type in Geranium Geraniaceae its use in classification and its evolutionary implications Botanical Journal of the Linnean Society 89 1 36 doi 10 1111 j 1095 8339 1984 tb00998 x PlantZAfrica com Homepage www plantzafrica com External links edit nbsp Look up awn in Wiktionary the free dictionary nbsp This plant morphology article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Awn botany amp oldid 1171257148, wikipedia, wiki, book, books, library,
