Late Cretaceous- present
name = Poaceae (true grasses)
image_width = 240px
image_caption = Flowering head of Meadow Foxtail ("
Alopecurus pratensis"), with stamens exserted at anthesis
divisio = Magnoliophyta
familia = Poaceae
familia_authority = (R.Br.) Barnhart
subdivision_ranks = Subfamilies
subdivision = There are 7 subfamilies:
Poaceae or Gramineae is a family in the Class
Liliopsidaof the flowering plants. Plants of this family are usually called grasses. There are about 600 genera and between 9,000–10,000 speciesof grasses (Kew Index of World Grass Species). Plant communities dominated by Poaceae are called grasslands; it is estimated that grasslands comprise 20% of the vegetation cover of the earth. This family is the most important of all plant families to human economies: it includes the staple foodgrains grown around the world, lawn and forage grasses, and bamboo, widely used for construction throughout east Asiaand sub-Saharan Africa.
The term "grass" is also applied to many grass-like plants not in the Poaceae, leading to plants of the Poaceae often being called "true grasses".
Structure and growth
Grasses generally have the following characteristics (it is advisable to have a look at the image gallery for reference):
Poaceae have hollow stems called "
culms", plugged at intervals called "nodes". Leaves are alternate, "distichous" (in one plane) or rarely spiral, parallel-veined and arise at the nodes. Each leaf is differentiated into a lower "sheath" hugging the stem for a distance and a "blade" with margin usually entire. The leaf blades of many grasses are hardened with silica phytoliths, which helps discourage grazing animals. In some grasses (such as sword grass) this makes the grass blades sharp enough to cut human skin. A membranous appendage or fringe of hairs, called the " ligule", lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath.
Grass blades grow at the base of the blade and not from growing tips. This location of the grass growing point near the ground allows it to be grazed or mowed regularly without damage to the growing point.cite book|title=
The Living Planet|author= David Attenborough|pages=113–4|publisher= British Broadcasting Corporation|id=ISBN 0-563-20207-6|year=1984]
Flowers of Poaceae are peculiar. They are characteristically arranged in "spikelets", each spikelet having one or more florets (the spikelets are further grouped into panicles or spikes). A spikelet consists of two (or sometimes fewer) bracts at the base, called "glumes", followed by one or more florets. A floret consists of the flower surrounded by two bracts called the "lemma" (the external one) and the "palea" (the internal). The flowers are usually hermaphroditic ( maize, monoecious, is an exception) and pollinationis always anemophilous. The perianthis reduced to two scales, called "lodicules", that expand and contract to spread the lemma and palea; these are generally interpreted to be modified sepals. This complex structure can be seen in the image on the left, portraying a wheat("Triticum aestivum") spike.
fruitof Poaceae is a " caryopsis".
Grass plants also spread out from a parent plant. Growth habit describes the type of shoot growth present in particular grass plants and is directly related to their ability to spread out from the parent plant and ultimately form a
clonal colony. There are three general classifications of growth habit present in grasses; bunch-type, stoloniferous, and rhizomatous.
Cool and Warm Season Grasses
The success of the grasses lies in part in their morphology and growth processes, and in part in their physiological diversity. The grasses divide into two physiological groups, using the C3 and C4 photosynthetic pathways for carbon fixation. The C4 grasses have a photosynthetic pathway linked to specialized Kranz leaf anatomy that particularly adapts them to hot climates and an atmosphere low in
C3 grasses are refereed to as "cool season grasses" while C4 plants are considered "warm season grasses". Cool and warm season grasses can be annual or perennial.
* Annual Cool Season -
wheat, rye, Annual Bluegrass, and oats
* Perennial Cool Season -
orchardgrass, fescue, Kentucky Bluegrassand perennial ryegrass
* Annual Warm Season -
corn, sudangrass, and pearlmillet
* Perennial Warm Season -
big bluestem, indiangrass, bermudagrass, switchgrass, and old world bluestems.
Source for annual and perennial cool and warm season grass names (above) = http://forages.oregonstate.edu/projects/regrowth/main.cfm?PageID=33
Until recently grasses were thought to have evolved around 55 million years ago, based on fossil records. However, recent findings of 65-million-year-old
phytoliths resembling grass phytoliths (including ancestors of riceand bamboo) in Cretaceous dinosaur coprolitescite journal
coauthors = Sues, H.D.
year = 2005
title = Dinosaurs Dined on Grass
journal = Science
volume = 310
issue = 5751
pages = 1126hor = Piperno, D.R.
doi = 10.1126/science.1121020
author = Piperno, D. R.
pmid = 16293745
unused_data = aut] cite journal
author = Prasad, V.
coauthors = Stroemberg, C.A.E.; Alimohammadian, H.; Sahni, A.
year = 2005
title = Dinosaur Coprolites and the Early Evolution of Grasses and Grazers
journal = Science(Washington)
volume = 310
issue = 5751
pages = 1177–1180
pmid = 16293759] , may place the diversification of grasses to an earlier date.
flowers of grass are reduced from the general monocotyledontype. The immediate ancestor of the first grass may have been a small Liliaceous plant with rhizomes and many small flowers, growing in dense patches, which adopted windpollination to escape limitations caused by shortage of insects to pollinatethe flowers.
ubfamilies and genera
The grass family has been divided into seven subfamilies:
Arundinoideae, including giant reed, common reed
Bambusoideae, including bamboo, rice
Centothecoideae, a small subfamily of 11 genera
Chloridoideae, including the windmill grasses
Panicoideae, including panic grass, maize, sorghum, sugar cane, most millets, bluestem grasses
Pooideae, including wheat, barley, oats
Stipoideae, including feather grass
Grasses are, in human terms, perhaps the most economically important plant family. Grasses' economic importance stems from several areas, including food production, industry, and lawns.
Agricultural grasses grown for their edible seeds are called "
cereals". Three cereals– rice, wheat, and maize(corn)– provide more than half of all calories eaten by humans.cite book|title=Understanding Biology|edition=3rd|author=Peter H. Raven & George B. Johnson|pages=536|id=ISBN 0-697-22213-6|year=1995|editor=Carol J. Mills (ed)|publisher=WM C. Brown] Of all crops, 70% are grasses.cite book|title=Grasslands and Tundra|publisher=Time Life Books|year=1985|series=Planet Earth|editor=George Constable (ed)|id=ISBN 0-8094-4520-4|pages=19] Cereals constitute the major source of carbohydratefor humans and perhaps the major source of protein, and include ricein southern and eastern Asia, maizein Central and South America, and wheatand barleyin Europe, northern Asia and the Americas. Sugarcaneis the major source of sugarproduction. Many other grasses are grown for forage and fodderfor animalfood, particularly for sheepand cattle. Some other grasses are of major importance for foliage production, thereby indirectly providing more human calories.
Grasses are used for construction.
Scaffoldingmade from bamboo is able to withstand typhoon force winds that would break steel scaffolding.cite book|title=Grasslands and Tundra|publisher=Time Life Books|year=1985|series=Planet Earth|editor=George Constable (ed)|id=ISBN 0-8094-4520-4|pages=20] Larger bamboos and " Arundo donax" have stout culms that can be used in a manner similar to timber, and grass roots stabilize the sod of sod houses. "Arundo" is used to make reeds for woodwind instruments, and bamboo is used for innumerable implements.
Grass fibre can be used for making
paper, and for biofuelproduction.
""Phragmites australis"" (common reed) is important in water treatment, wetland habitat preservation and land reclamation in the
Grasses are the primary plant used in
lawns, which themselves derive from grazed grasslands in Europe.
Although supplanted by
artificial turfin some games, grasses are still an important covering of playing surfaces in many sports, including football, tennis, golf, cricket, and softball/ baseball.
Economically important grasses
With 10,025 known species, the Poaceae is the fourth largest . Only
Orchidaceae, Asteraceae, and Fabaceaehave more species, although with over 10,000 species the Rubiaceaeis not far behind.cite web|url=http://www.mobot.org/MOBOT/Research/APweb/welcome.html#Famlarge|title=Angiosperm phylogeny website|accessdate=2007-10-07] Biomes dominated by grasses are called grasslands. If only large contiguous chunks of grasslands are counted, these biomes cover 31% of the planet's land. Grasslands go by various names depending on location, including pampas, plains, steppes, or prairie.
Grasses are used as food plants by many species of
butterfliesand moths; see List of Lepidoptera that feed on grasses.
The evolution of large grazing animals in the
Cenozoichas contributed to the spread or grasses. Without large grazers, a clearcut of fire-destroyed area would soon be colonized by grasses and, if there is enough rain, tree seedlings. The tree seedlings would eventually produce shade, which kills most grasses. Large animals, however, trample the seedlings, killing the trees. Grasses persist because they can survive trampling.cite book|title= The Living Planet|author= David Attenborough|pages=137|publisher= British Broadcasting Corporation|year=1984]
Grass and society
Grass has long had significance in human society. It has been cultivated as a food source for
domesticated animalsfor up to 10,000 years, and has been used to make papersince at least as early as 2400 B.C.
aphorisms involve grass. For example:
*"The grass is always greener on the other side" suggests that an alternate state of affairs will always seem preferable to one's own.
*"Don't let the grass grow under your feet" tells someone to get moving.
snakein the grass" means dangers that are hidden.
elephantsfight, it is the grass who suffers" tells of bystanders caught in the crossfire.
*Chapman, G.P. and W.E. Peat. 1992. An Introduction to the Grasses. CAB International, Wallingford.
*Cheplick, G.P. 1998. Population Biology of Grasses. Cambridge Univ. Press, Cambridge.
* [http://www.turffiles.ncsu.edu TurfFiles] by
North Carolina State University
* [http://www.rbgkew.org.uk/data/grasses-db/sppindex.htm Kew Index of World Grass Species]
* [http://forages.oregonstate.edu/projects/regrowth/main.cfm?PageID=11 Definitions of Grass structures]
* [http://delta-intkey.com/angio/www/graminea.htm The grass genera of the world, L. Watson and M. J. Dallwitz] (1992 onwards)
* [http://delta-intkey.com/angio/ The families of flowering plants.]
* [http://delta-intkey.com/grass/ The grass genera of the world]
* [http://www.sciencemag.org/cgi/content/summary/310/5751/1126 Content summary] .
* [http://utc.usu.edu/keys/default.htm Interactive Keys to North American Grasses at Utah State University]
* [http://flowersinisrael.com/FamGraminea%20(Poaceae).html Family Gramineae] Flowers in Israel
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Look at other dictionaries:
Poaceae — Poaceae … Wikipédia en Français
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Poaceae — ▪ plant family Introduction formerly called Gramineae grass family of monocotyledonous flowering plants, a division of the order Poales. The Poaceae are the world s single most important source of food. They rank among the top five… … Universalium
Poaceae — noun the grasses: chiefly herbaceous but some woody plants including cereals; bamboo; reeds; sugar cane • Syn: ↑Gramineae, ↑family Gramineae, ↑Graminaceae, ↑family Graminaceae, ↑family Poaceae, ↑grass family • Hypernyms: ↑ … Useful english dictionary
Poaceae — … Википедия
poaceae — po·a·ce·ae … English syllables
Poaceae (Gramineae) — Сем. Злаки 25. Echinochloa Beauv. – Ежовник 26. Setaria Beauv. – Щетинник 27. Phalaroides N. М. Wolf. – Двукисточник 28. Anthoxanthum – Душистый колосок 29. Hierochloë R. Br. – Зубровка 30. Milium L. – Бор … Флора Центрально-лесного государственного заповедника