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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 various plant families, including Geraniaceae and many grasses (Poaceae).
Among grasses with awns are those commonly known as foxtails, which tend to stick to animals passing by the plant.
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).
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]
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]
Emmer wheat or hulled wheat is a type of awned wheat. Emmer is a tetraploid. The domesticated types are Triticum turgidum subsp. dicoccum and T. t. conv. durum. The wild plant is called T. t. subsp. dicoccoides. The principal difference between the wild and the domestic forms is that the ripened seed head of the wild plant shatters and scatters the seed onto the ground, while in the domesticated emmer, the seed head remains intact, thus making it easier for humans to harvest the grain.
Andropogon gerardi, commonly known as big bluestem, is a species of tall grass native to much of the Great Plains and grassland regions of central and eastern North America. It is also known as tall bluestem, bluejoint, and turkeyfoot.
A spikelet, in botany, describes the typical arrangement of the flowers of grasses, sedges and some other monocots.
A foxtail is a spikelet or cluster of a grass, that serves to disperse its seeds as a unit. Thus, the foxtail is a type of diaspore or plant dispersal unit. Some grasses that produce a foxtail are themselves called "foxtail", also "spear grass". They can become a health hazard for dogs, cats, and other domestic animals, and a nuisance for people.
Avena sterilis is a species of grass weed whose seeds are edible. Many common names of this plant refer to the movement of its panicle in the wind.
Bouteloua gracilis, the blue grama, is a long-lived, warm-season (C4) perennial grass, native to North America.
Lolium perenne, common name perennial ryegrass, English ryegrass, winter ryegrass, or ray grass, is a grass from the family Poaceae. It is native to Europe, Asia and northern Africa, but is widely cultivated and naturalised around the world.
Hordeum jubatum, with common names foxtail barley, bobtail barley, squirreltail barley, and intermediate barley, is a perennial plant species in the grass family Poaceae. It occurs wild mainly in northern North America and adjacent northeastern Siberia. However, as it escaped often from gardens it can be found worldwide in areas with temperate to warm climates, and is considered a weed in many countries. The species is a polyploid and originated via hybridization of an East Asian Hordeum species with a close but extinct relative of Californian H. brachyantherum. It is grown as an ornamental plant for its attractive inflorescences and when done flowering for its inflorescence.
Aegilops triuncialis, or barbed goatgrass, is a grass species of the family Poaceae. It is a winter annual native to many areas in Eastern and Mediterranean Europe and Western Asia. It is considered an introduced, invasive species in North America, mainly in the Western coast of the United States. In its native lands, the grass thrives in mainly rocky, serpentine soil, but also does well in grasslands and ruderal/disturbed ground as well as oak woodlands.
Agropyron cristatum, the crested wheat grass, crested wheatgrass, fairway crested wheat grass, is a species in the family Poaceae. This plant is often used as forage and erosion control. It is well known as a widespread introduced species on the prairies of the United States and Canada.
Erodium cicutarium, also known as common stork's-bill, redstem filaree, redstem stork's bill or pinweed, is a herbaceous annual – or in warm climates, biennial – member of the family Geraniaceae of flowering plants. It is native to Macaronesia, temperate Eurasia and north and northeast Africa, and was introduced to North America in the eighteenth century, where it has since become naturalized, particularly of the deserts and arid grasslands of the southwestern United States.
Bromus hordeaceus, the soft brome, is an annual or biennial species of grass in the grass family (Poaceae). It is also known in North America as bull grass, soft cheat, and soft chess.
Hordeum pusillum, also known as little barley, is an annual grass native to most of the United States and southwestern Canada. It arrived via multiple long-distance dispersals of a southern South American species of Hordeum about one million years ago. Its closest relatives are therefore not the other North American taxa like meadow barley or foxtail barley, but rather Hordeum species of the Pampas of central Argentina and Uruguay. It is less closely related to the Old World domesticated barley, from which it diverged about 12 million years ago. It is diploid.
Bromus diandrus is a species of grass known by the common names great brome and "ripgut brome".
Bromus madritensis is a species of brome grass known by the common name compact brome. The specific epithet madritensis refers to Madrid, Spain. It has a diploid number of 28.
This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology, Glossary of lichen terms, and List of Latin and Greek words commonly used in systematic names.
Stipa speciosa (syn. Achnatherum speciosum is a species of grass known by the common name desert needlegrass. It is native to much of the south-western United States from California to Colorado, where it grows in dry areas, especially sagebrush habitat. It is also known from Mexico and parts of South America.
Piptochaetium avenaceum, commonly called black oat grass, blackseed needle grass or blackseed speargrass, is a species of perennial bunchgrass native to eastern North America. It is a member of the grass family Poaceae.
Hesperostipa spartea, formerly Stipa spartea, is a species of grass known by the common names porcupine grass, western porcupine grass, short-awn porcupine grass, porcupine needlegrass, and big needlegrass. It is native to North America, where it is widespread from British Columbia to Ontario in Canada and through the central and Great Lakes regions of the United States. It is a bunchgrass species in the genus Hesperostipa.
Rytidosperma bipartitum, the leafy wallaby grass, is a perennial species of grass found in south eastern Australia. Usually found on the heavier clay or on loamy soils in open eucalyptus woodland. The habit is somewhat variable, erect and densely tufted. The grass may grow up to 0.7 m tall.
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