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Grass (Poaceae or Gramineae)

Saltgrass
Distichlis
spicata

Image source: [ 5 ]
Silver tussock
Poa
caespitosa

Image source: University of Newcastle [ 6 ]
Bearded wheatgrass
Agropyron trachycaulum
Image source: [ 5 ]

Grass typically refers to any of the low, green, nonwoody plants which belong to the grass family ( Poaceae or Gramineae ), sedge family ( Cyperaceae ) or rush family ( Juncaceae ). However, it is only the Poaceae/Gramineae family, which are true grasses. This family, part of the plant order Cyperales , contains between 500 and 650 genera with a total of anything up to 10,000 species.
The grass family is both the most common and important family of flowering plants. Poaceae are found virtually everywhere, in every type of habitat and are the world's most important foodstuff. They provide animal forage, food (especially the cereal grasses such as rice, corn, millet and wheat), turf for lawns, construction materials, utensils and shelter. The success of the grasses is due to the fact that they can withstand grazing. New plant growth can not occur if the shoot tip is removed and the grasses are unique in that the shoot tip is at the stem base, thus they withstand being mowed or grazing.
The Poaceae are generally divided into 5 (or 6) subfamilies: Pooideae, Panicoideae, Bambusoideae, Chloridoideae, Arundinoideae and sometimes Oryzoideae, a subtype of Bambusoideae. These subfamilies are further divided into tribes.
Poaceae are characterised by their long, narrow leaves which form sheaths around the stem and flowers lacking in petals and sepals. The roots are generally fibrous and branching with an extensive underground network or surface stems. Thus, grasses prevent soil erosion. [ 1 ]
The grass pollen images on the right are all typical members of the Poaceae/Gramineae family. See also the information on tree and weed pollens.

The following are some of the grasses specifically mentioned in relation
to causing seasonal allergic reactions in certain individuals:

Annual Bluegrass Kentucky Bluegrass Ryegrass
Sweet Vernal Kikuyu Redtop
Bermuda Grass Orchard Grass Timothy Grass
Love Grasses Paspalum  

 

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Annual Bluegrass. Poa annua . Annual bluegrass is a winter annual that germinates in the late summer/early autumn. Seedlings mature in the fall, overwinter in a vegetative state, and produce seed in late spring and early summer. Annual bluegrass is a prolific seed producer. Annual bluegrass grows well even in cool conditions and short days but the Summer heat may kill it. Often used on golfcourses due to its robust nature. [ 4 ]
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Anthoxanthum . Also called sweet vernal or simply vernal grass. A genus of about 4 four species of fragrant annual and perennial grasses.Thin, flat leaves contain coumarin which is released as a sweet scent when it is cut for hay. [ 1 ]
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Bermuda Grass. Cynodon dactylon . Also referred to as Bermuda couch grass, this grass is probably of Asian origin and has been an important grass in the USA since 1807 (first documented). Bermudagrass is a long-lived, warm season perennial often used for critical area planting (e.g. channels and pond banks), grassed waterways, and vegetated flumes and as a hardy, weed-resistant turf for lawns and public areas. Also used for pasture and hay. [ 2 ]
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Eragrostis . Commonly known as the love grasses. About 250 species are known and are usually native to the tropical and temperate regions of the globe. Plains love grass ( E. intermedia ), sand love grass ( E. trichodes ), and weeping love grass ( E. curvula ) are species in often used as forage, most typically in the southern states of the USA. Weeping love grass, is a native of South Africa, and has been introduced elsewhere as an ornamental and is often used to prevent erosion. Stink grass ( E. cilianensis ) is a weedy, coarse annual, native to Mediterranean regions, which has a musty odour produced by the glands on its leaves. Can prove to be poisonous to livestock if consumed in large amounts. [ 1 ]
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Kentucky Bluegrass. Poa pratensis. Kentucky bluegrass, is a perennial, cool-season, sod-forming grass native to Europe, which is present throughout most of the US. Kentucky bluegrass begins to grow early in Spring and usually becomes dormant during the hot Summer period. Kentucky bluegrass is a sturdy grass, which is often used for lawns, parks, golf courses and erosion control due to its long, fibrous roots. It is also highly palatable to a wide range of animals, hence its frequent use as a grazing grass. The leaves are of a blueish tint, hence the name. [ 2 ]
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Kikuyu. Pennisetum clandestinum . A dense, creeping grass, which forms a dense turf resistant to heavy grazing. [ 3 ]
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Orchard Grass. Dactylis glomerata. A persistent, cool season bunchgrass, primarily used for forage production as it is highly palatable to all classes of livestock. Also used in erosion control due to its dense root network. Orchardgrass is found from Maine to the Gulf Coast states and from the Atlantic Coast to the eastern Great Plains. It is common throughout the Appalachian Mountains and is especially well-adapted to Maryland, Pennsylvania, West Virginia, Virginia, Kentucky, and Tennessee. It is also found in the high-rainfall regions of the western mountains and in irrigated areas throughout the West. [ 2 ]
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Paspalum. A genus of annual and perennial grasses of the Poaceae family, consisting of around 400 species. Typically found in the warmer regions of the globe. Certain species such as dallis grass ( P. dilatatum) and vasey grass (P. urvillei) are valued as forage. A common species of Paspalum is the water couch, or knotgrass ( P. distichum), which is found along shores and in ditches in the Americas and Europe, while also being used as a lawn grass in Australia. [ 1 ]
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Perennial Ryegrass. Lolium perenne . A valuable forage and soil stabilization plant, which is the predominant forage grass species present in Europe, as well as being used as turf for lawns in both the USA and Europe. [ 2 ]
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Redtop. Agrostis gigantea . A perennial grass, which produces a coarse but dense turf. Used for erosion control, pastures and occasionally for hay. It is often used for stabilising critical areas, since it germinates rapidly. One of the most widely adapted grasses in North America as it can grow in a wide variety of moisture and soil conditions and is drought-resistant. [ 2 ]
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Timothy Grass. Phleum pratense. A relatively short-lived, cool-season perennial, which differs from most other grasses in that one of the basal internodes of the stem can occasionally swell into a bulb-like growth. Used for pasture, silage and especially hay. [ 2 ]
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[1] The Encyclopaedia Britannica Online : http://www.britannica.com
[2] Grass Fact sheets : http://Plant-Materials.nrcs.usda.gov
[3] The State of New South Wales, NSW Agriculture, 1995 : http://www.dpi.qld.gov.au
[4] Purdue University's Agronomy Department, West Lafayette, IN, USA : http://www.agry.purdue.edu
[5] Solomon, A.M., King, J.E., Martin, P.S. and Thomas, J., 1973. "Further scanning electron photomicrographs of southwestern pollen grains." Journal Arizona Academy of Sciences 8 (3): 135 - 157. Palynology Department, University of Arizona : http://geo.arizona.edu/palynology
[6] The Geomorphology and Quaternary Science Research Unit, School of Geosciences, University of Newcastle, Callaghan, NSW, 2083, Australia : http://www.newcastle.edu.au/

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  http://www.hon.ch/Library/Theme/Allergy/Glossary/grass.html Last modified: Wed Oct 20 2004