The Poaceae (English pronunciation: /poʊˈeɪ.siˌiː/) or Gramineae are the large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses. The Poaceae include the cereal grasses, bamboos and the grasses of natural grassland and cultivated lawns (turf) and pasture. Grasses have stems that are hollow except at the nodes and narrow alternate leaves borne in two ranks. The lower part of each leaf encloses the stem, forming a leaf-sheath. With more than 10,000 species,, the Poaceae are the fourth-largest plant family following the Asteraceae, Orchidaceae and Fabaceae.
The name Poaceae was given by John Hendley Barnhart in 1895, based on the tribe Poeae (described in 1814 by Robert Brown), and the type genus Poa (described in 1753 by Carl Linnaeus). The term is derived from the Ancient Greek term for grass.
Description
Grasses generally have the following characteristics (the image gallery can be used for reference): The stems of grasses, called culms are usually cylindrical (more rarely flattened, but not 3-angled) and are hollow, plugged at the nodes, where the leaves are attached. Grass leaves are nearly always alternate and distichous (in one plane), and have parallel veins. Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins. The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals; some, such as sword grass, are 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.
Flowers of Poaceae are characteristically arranged in spikelets, each having one or more florets. The spikelets are further grouped into panicles or spikes. The part of the spikelet that bears the florets is called the rachilla. 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, one external—the lemma-and one internal—the palea. The flowers are usually hermaphroditic, maize, being an important exception—and anemophilous or wind-pollinated. The perianth is 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 right, portraying a wheat (Triticum aestivum) spikelet. The fruit of grasses is a caryopsis, in which the seed coat is fused to the fruit wall. A tiller is a leafy shoot other than the first shoot produced from the seed.
Grass blades grow at the base of the blade and not from elongated stem tips. This low growth point evolved in response to grazing animals and allows grasses to be grazed or mown regularly without severe damage to the plant. Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), stoloniferous and rhizomatous. The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. Most of 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, which allows for increased water use efficiency, rendering them better adapted to hot, arid environments and those lacking in carbon dioxide.
The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent, and are absent only from central Greenland-and much of Antarctica.
Ecology
Grasses are the dominant vegetation in many habitats, including grassland, salt-marsh, reedswamp and steppes. They also occur as a smaller part of the vegetation in almost every other terrestrial habitat. Grass-dominated biomes are called grasslands. If only large, contiguous areas of grasslands are counted, these biomes cover 31% of the planet's land.
Grasslands include pampas, steppes and prairies. Grasses provide food to many grazing mammals—such as livestock, deer, and elephants—as well as to many species of butterflies and moths. Many types of animals eat grass as their main source of food, and are called graminivores- these include cattle sheep, horses, rabbits and many invertebrates such as grasshoppers and the caterpillars of many brown butterflies.
Grasses are also eaten by omnivorous or even occasionally by primarily carnivorous animals. Grasses are unusual in that the meristem is located near the bottom of the plant, hence can quickly recover from cropping at the top. The evolution of large grazing animals in the Cenozoic contributed to the spread of grasses. Without large grazers, fire-cleared areas are quickly colonized by grasses, and with enough rain, tree seedlings. Trees eventually shade out and kill most grasses. Trampling grazers kill seedling trees but not grasses.
Evolution
Grasses include some of the most versatile plant life-forms. They became widespread toward the end of the Cretaceous period, and fossilized dinosaur dung (coprolites) have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo. Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are now the most widespread plant type; grass is a valuable source of food and energy for all sorts of wildlife and organics.
Depending on the classification scheme followed, the family includes about 668 genera. See the full list of Poaceae genera.
Uses
Grasses are, in human terms, perhaps the most economically important plant family. Their economic importance stems from several areas, including food production, industry, and lawns. They have been grown as food for domesticated animal, for up to 6,000 years and the grains of grasses such as wheat, rice, maize (corn) and barley have been the most important human food crops. Grasses are also used in the manufacture of thatch, paper, fuel, clothing, insulation, timber for fencing, furniture, scaffolding and construction materials, sports turf and baskets.
Food Production
Industry
Grasses are the primary plant used in lawns which themselves derive from grazed grasslands in Europe. They also provide an important means of erosion control (e.g., along roadsides), especially on sloping land. Grass lawns are an important covering of playing surfaces in many sports, including football (soccer), tennis, golf, cricket softball and baseball.
Sports Turfs
Grass playing fields, courses and pitches are the traditional playing surfaces for many sports, such as American football , Association football, baseball, cricket, and rugby and golf. Sports such as golf, tennis and cricket are particularly dependent on the quality of the grass on which the sport is played. In some sports facilities, including indoor domes and other places where maintenance of a grass field would be difficult, grass may be replaced with artificial turf, a synthetic grass-like substitute.
Crickets
In cricket, the pitch is the strip of carefully mowed and rolled grass where the bowler bowls. In the days leading up to the match it is repeatedly mowed and rolled to produce a very hard, flat surface for the ball to bounce off.
Golf
Grass on golf courses is kept in three distinct conditions: that of the rough, the fairway, and the putting green. Grass on the fairway is mown short and even, allowing the player to strike the ball cleanly. Playing from the rough is a disadvantage because the long grass may affect the flight of the ball. Grass on the putting green is the shortest and most even, ideally allowing the ball to roll smoothly over the surface. An entire industry revolves around the development and marketing of grass varieties for golf courses.
Economically Important Grasses
Tennis
In tennis, grass is grown on very hard-packed soil, and the bounce of a tennis-ball may vary depending on the grass's health, how recently it has been mowed, and the wear and tear of recent play. The surface is softer than hard courts and clay (other tennis surfaces), so the ball bounces lower, and players must reach the ball faster resulting in a different style of play which may suit some players more than others. The world's most famous grass tennis is Centre Court at Wimbledon in England, home of the Wimbledon Championship.
Grass and Society
Grasses have long had significance in human society. They have been cultivated as feed for people and domesticated animals for thousands of years. The primary ingredient of beer is usually barley or wheat, both of which have been used for this purpose for over 4,000 years.
References
Grasslands such as savannah and prairie where grasses are dominant are estimated to constitute 20% of the vegetation cover of the Earth. Grasses are also an important part of the vegetation in many other habitats, including wetlands, forests and tundra. The Poaceae are the most economically important plant family, providing staple foods from domesticated cereal, crops such as maize (corn), wheat, rice, barley and millet as well as forage, building materials (bamboo,, thatch, straw) and fuel (ethanol).
Though commonly called "grasses", seagrasses rushes and sedges fall outside this family (see Grass (disambiguation). The rushes and sedges are related to the Poaceae, being members of the order Poales but the seagrasses are members of order Alismatales.
EtymologyThe name Poaceae was given by John Hendley Barnhart in 1895, based on the tribe Poeae (described in 1814 by Robert Brown), and the type genus Poa (described in 1753 by Carl Linnaeus). The term is derived from the Ancient Greek term for grass.
Description
Grasses generally have the following characteristics (the image gallery can be used for reference): The stems of grasses, called culms are usually cylindrical (more rarely flattened, but not 3-angled) and are hollow, plugged at the nodes, where the leaves are attached. Grass leaves are nearly always alternate and distichous (in one plane), and have parallel veins. Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins. The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals; some, such as sword grass, are 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.
Diagram of a typical lawn grass plant.
Flowers of Poaceae are characteristically arranged in spikelets, each having one or more florets. The spikelets are further grouped into panicles or spikes. The part of the spikelet that bears the florets is called the rachilla. 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, one external—the lemma-and one internal—the palea. The flowers are usually hermaphroditic, maize, being an important exception—and anemophilous or wind-pollinated. The perianth is 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 right, portraying a wheat (Triticum aestivum) spikelet. The fruit of grasses is a caryopsis, in which the seed coat is fused to the fruit wall. A tiller is a leafy shoot other than the first shoot produced from the seed.
Parts of a spikelet
Growth and Development
Grass blades grow at the base of the blade and not from elongated stem tips. This low growth point evolved in response to grazing animals and allows grasses to be grazed or mown regularly without severe damage to the plant. Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), stoloniferous and rhizomatous. The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. Most of 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, which allows for increased water use efficiency, rendering them better adapted to hot, arid environments and those lacking in carbon dioxide.
Grass flowers
The C3 grasses are referred to as "cool-season" grasses, while the C4 plants are considered "warm-season" grasses; they may be either annual or perennial.
- Annual cool-season - wheat, rye annual bluegrass (annual meadowgrass, Poa annu) and oat
- Perennial cool-season - orchardgrass (cocksfoot, Dactylis glomerata). fescue (Festuca spp.), Kentucky bluegrass and perennial ryegrass (Lolium perenne).
- Annual warm-season - maize sudangrass and pearl millet.
- Perennial warm-season - big bluestem, Indiangrass, Bermudagrass and switchgrass.
The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent, and are absent only from central Greenland-and much of Antarctica.
Ecology
Grasses are the dominant vegetation in many habitats, including grassland, salt-marsh, reedswamp and steppes. They also occur as a smaller part of the vegetation in almost every other terrestrial habitat. Grass-dominated biomes are called grasslands. If only large, contiguous areas of grasslands are counted, these biomes cover 31% of the planet's land.
A kangaroo eating grass
Grasslands include pampas, steppes and prairies. Grasses provide food to many grazing mammals—such as livestock, deer, and elephants—as well as to many species of butterflies and moths. Many types of animals eat grass as their main source of food, and are called graminivores- these include cattle sheep, horses, rabbits and many invertebrates such as grasshoppers and the caterpillars of many brown butterflies.
Wind-blown grass in the Valles Caldera in New Mexico
Grasses are also eaten by omnivorous or even occasionally by primarily carnivorous animals. Grasses are unusual in that the meristem is located near the bottom of the plant, hence can quickly recover from cropping at the top. The evolution of large grazing animals in the Cenozoic contributed to the spread of grasses. Without large grazers, fire-cleared areas are quickly colonized by grasses, and with enough rain, tree seedlings. Trees eventually shade out and kill most grasses. Trampling grazers kill seedling trees but not grasses.
Evolution
Grasses include some of the most versatile plant life-forms. They became widespread toward the end of the Cretaceous period, and fossilized dinosaur dung (coprolites) have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo. Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are now the most widespread plant type; grass is a valuable source of food and energy for all sorts of wildlife and organics.
Until recently, fossil findings indicated that grasses evolved around 55 million years ago. Recent findings of grass-like phytoliths in Cretaceous dinosaur coprolites have pushed this date back to 66 million years ago. Indeed, revised dating of the origins of the rice tribe Oryzeae suggest a date as early as 107 to 129 Mya.
The relationships among the subfamilies Bambusoideae, Oryzoideae and Pooideae in the BOP clade have been resolved: Bambusoideae and Pooideae are more closely related to each other than to Oryzoideae. This separation occurred within a relatively short time span (about 4 million years).
Taxonomy
Setaria verticillata from Panicoideae.
Depending on the classification scheme followed, the family includes about 668 genera. See the full list of Poaceae genera.
Recent classifications of the grass family recognize 12 subfamilies and a small number of taxa with uncertain placements:
Tragus roxburghii from Chloridoideae
- Anomochlooideae, Pilg ex Potztal, a small lineage of broad-leaved grasses that includes two genera (Anomochloa, Streptochaeta)
- Pharoideae L.G.Clark & Judz a small lineage of grasses of three genera, including Pharus and Leptaspis
- Puelioideae L.G.Clark, M.Kobay, S.Mathews Spangler & E.A.Kellogg, a small lineage of the African genus Puelia
- Pooideae, including wheat, barley, oats, brome-grass (Bromus), reed-grasses (Calamagrostis) and many lawn and pasture grasses
- Bambusoideae, including bamboo.
- Ehrhartoideae, including rice and wild rice.
- Aristidoideae, including Aristida.
- Arundinoideae, including giant reed and common reed.
- Chloridoideae, including the lovegrasses (Eragrostis, about 350 species, including teff), dropseeds (Sporobolus, some 160 species), finger millet (Eleusine coracana (L.) Gaertn.), and the muhly grasses (Muhlenbergia, about 175 species)
- Panicoideae, including panic grass, maize, sorghum, sugarcane, most millets, fonio, and bluestem grasses.
- Micrairoideae
- Danthonioideae, including pampas grass
Grasses are, in human terms, perhaps the most economically important plant family. Their economic importance stems from several areas, including food production, industry, and lawns. They have been grown as food for domesticated animal, for up to 6,000 years and the grains of grasses such as wheat, rice, maize (corn) and barley have been the most important human food crops. Grasses are also used in the manufacture of thatch, paper, fuel, clothing, insulation, timber for fencing, furniture, scaffolding and construction materials, sports turf and baskets.
Grazing cattle on a pasture near Hradec nad Moravicí in Czech Silesia.
Food Production
Agricultural grasses grown for their edible seeds are called cereals or grains (although the latter term, agriculturally, refers to both cereals and legumes. Three cereals – rice, wheat and maize (corn) – provide more than half of all calories eaten by humans. Of all crops, 70% are grasses. Cereals constitute the major source of carbohydrates for humans and perhaps the major source of protein, and include rice in southern and eastern Asi, maize in Central and South America and wheat and barley in Europe, northern Asia and the Americas.
Sugarcane is the major source of sugar production. Additional food uses include sprouted grain, shoot, rhizomes and sugar, drink (sugarcane juice, plant milk, rum, beer, whisky, vodka.
Many species of grasses are grown as pasture for forage and fodder, for livestock, particularly for sheep and cattle. They may be cut and stored in the form of hay, straw or silage for use during the winter. Hay and straw are used for animal bedding.Industry
Grasses are used as raw material for a multitude of purposes, including construction and in the composition of building materials such as cob, for insulation, in the manufacture of paper and board, and as fuel. Scaffolding, made from bamboo is able to withstand typhoon-force winds that would break steel scaffolding. Larger bamboos and Arundo donax have stout culms that can be used in a manner similar to timber, Arundo is used to make reeds for woodwind instruments, and bamboo is used for innumerable implements.
Grass fiber can be used for making paper, and for biofuel production.
Phragmites australis (common reed) is important for thatching and grass roots stabilize the sod of sod houses. Reeds are used in water treatment systems, in wetland conservation and land reclamation in Afro-Eurasia, Marram grass (Ammophila arenaria)
Lawn and Ornamental GrassesGrasses are the primary plant used in lawns which themselves derive from grazed grasslands in Europe. They also provide an important means of erosion control (e.g., along roadsides), especially on sloping land. Grass lawns are an important covering of playing surfaces in many sports, including football (soccer), tennis, golf, cricket softball and baseball.
A lawn in front of a building
Ornamental grasses, such as perennial, bunch grasses, are used in many styles of garden design for their foliage, inflorescences, seed heads. They are often used in natural landscaping, xeriscaping and slope stabilization in contemporary landscaping, wildlife gardening and native plant gardening.
Sports Turfs
Grass playing fields, courses and pitches are the traditional playing surfaces for many sports, such as American football , Association football, baseball, cricket, and rugby and golf. Sports such as golf, tennis and cricket are particularly dependent on the quality of the grass on which the sport is played. In some sports facilities, including indoor domes and other places where maintenance of a grass field would be difficult, grass may be replaced with artificial turf, a synthetic grass-like substitute.
Forms of grass are used to cover baseball fields, like this one in Citi Field, home of the Mets.
Crickets
In cricket, the pitch is the strip of carefully mowed and rolled grass where the bowler bowls. In the days leading up to the match it is repeatedly mowed and rolled to produce a very hard, flat surface for the ball to bounce off.
The gray area is the cricket pitch currently in use. Parallel to it are other pitches in various states of preparation which could be used in other matches.
Golf
Grass on golf courses is kept in three distinct conditions: that of the rough, the fairway, and the putting green. Grass on the fairway is mown short and even, allowing the player to strike the ball cleanly. Playing from the rough is a disadvantage because the long grass may affect the flight of the ball. Grass on the putting green is the shortest and most even, ideally allowing the ball to roll smoothly over the surface. An entire industry revolves around the development and marketing of grass varieties for golf courses.
Economically Important Grasses
Tennis
In tennis, grass is grown on very hard-packed soil, and the bounce of a tennis-ball may vary depending on the grass's health, how recently it has been mowed, and the wear and tear of recent play. The surface is softer than hard courts and clay (other tennis surfaces), so the ball bounces lower, and players must reach the ball faster resulting in a different style of play which may suit some players more than others. The world's most famous grass tennis is Centre Court at Wimbledon in England, home of the Wimbledon Championship.
Grass and Society
Grasses have long had significance in human society. They have been cultivated as feed for people and domesticated animals for thousands of years. The primary ingredient of beer is usually barley or wheat, both of which have been used for this purpose for over 4,000 years.
In some places, particularly in suburban areas, the maintenance of a grass lawn is a sign of a homeowner's responsibility to the overall appearance of their neighborhood. One work credits lawn maintenance to:
Grass-covered house in Iceland.
Many municipalities and homeowners' associations have rules which require lawns to be maintained to certain specifications, sanctioning those who allow the grass to grow too long. In communities with drought problems, watering of lawns may be restricted to certain times of day or days of the week. The smell of the freshly cut grass is produced mainly by cis-3-Hexenal. Some common aphorisms involve grass. For example:
- "The grass is always greener on the other side" suggests 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.
- "A snake in the grass" means dangers that are hidden.
- "When elephants fight, it is the grass which suffers" tells of bystanders caught in the crossfire.
A folk myth about grass is that it refuses to grow where any violent death has occurred.
Grass in Literature - In John Christopher's The Death of Grass, 1956, published in the United States as No Blade of Grass), a plague that kills off all forms of grass threatens the survival of the human species.
- In Ward Moore's novel Greener Than You Think, the world is slowly taken over by unstoppable Bermuda Grass.
- Alice Munro's story "Save the Reaper", (1998) contains an important allusion to the idiomatic saying, "To hear the grass grow"; the aging protagonist remembers her grandfather's telling her when she was young that "at night you could hear the corn growing" in the region where the story is set. The protagonist hears the grass grow in ways that are central to the story's significance on the topic of retelling, or rather, in an act of self-censorship, of leaving untold certain experiences of the recent past.
- The title of Walt Whitman's poetry collection Leaves of Grass (1855) contains two puns: "leaves", referring to the pages on which the book was written, and "grass", a term given by publishers to works of minor value.
- ^ a b Piperno, Dolores R.; Sues, Hans-Dieter (2005). "Dinosaurs Dined on Grass". Science310 (5751): 1126–8. doi:10.1126/science.11210. PMID 16293745.
- ^ Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. (PDF). Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. Retrieved 2013-06-26.
- ^ a b Stevens, P.F. "Angiosperm Phylogeny Website". Retrieved 2007-10-07.
- ^ Barnhart, J.H. (1895). "Poaceae". Bulletin of the Torrey Botanical Club 22: 7.
- ^ David Attenborough (1984). The Living Planet. British Broadcasting Corporation. pp. 113–4. ISBN 0-563-20207-6.
- ^ Sarandón, Ramiro (1988). "Biología poblacional del gramon (Cynodon spp., gramineae)". 189. Retrieved 22 April 2014.
- The dictionary definition of grass, at Wiktionary
- Need a Definition of Grass?
- Vegetative Key to Grasses
- Poaceae, at The Plant List.
- Gramineae, at The Families of Flowering Plants (DELTA).
- Poaceae, at the Encyclopedia of Life.
- Poaceae, at the Angiosperm Phylogeny Website.
- Poaceae Classification, from the online Catalogue of New World Grasses.
- Poaceae at the online Flora of China
- Wikipedia
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