Poaceae

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Grasses
Temporal range: Albian–Present
Meadow Foxtail head.jpg
Flowering head of meadow foxtail ( Alopecurus pratensis ), with stamens exerted at anthesis
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Clade: Graminid clade
Family: Poaceae
Barnhart [2]
Type genus
Poa
L.
Subfamilies
Synonyms [3]

Gramineae  Juss.

Poaceae ( /pˈsi/ ) or Gramineae is a large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and pasture. The latter are commonly referred to collectively as grass.

Contents

With around 780 genera and around 12,000 species, [4] the Poaceae is the fifth-largest plant family, following the Asteraceae, Orchidaceae, Fabaceae and Rubiaceae. [5]

The Poaceae are the most economically important plant family, providing staple foods from domesticated cereal crops such as maize, wheat, rice, barley, and millet as well as feed for meat-producing animals. They provide, through direct human consumption, just over one-half (51%) of all dietary energy; rice provides 20%, wheat supplies 20%, maize (corn) 5.5%, and other grains 6%. [6] Some members of the Poaceae are used as building materials (bamboo, thatch, and straw); others can provide a source of biofuel, primarily via the conversion of maize to ethanol.

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. The leaf grows from the base of the blade, an adaptation allowing it to cope with frequent grazing.

Grasslands such as savannah and prairie where grasses are dominant are estimated to constitute 40.5% of the land area of the Earth, excluding Greenland and Antarctica. [7] Grasses are also an important part of the vegetation in many other habitats, including wetlands, forests and tundra.

Though they are commonly called "grasses", seagrasses, rushes, and sedges fall outside this family. The rushes and sedges are related to the Poaceae, being members of the order Poales, but the seagrasses are members of order Alismatales.

Etymology

The name Poaceae was given by John Hendley Barnhart in 1895, [8] :7 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 πόα (póa, "fodder").

Evolutionary history

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. [9] Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are currently the most widespread plant type; grass is a valuable source of food and energy for all sorts of wildlife and organics.

A cladogram shows subfamilies and approximate species numbers in brackets: [10]

PACMAD clade

Chloridoideae (1600)

Danthonioideae (300)

Micrairoideae (200)

Arundinoideae (50)

Panicoideae (3250)

Aristidoideae (350)

BOP clade

Oryzoideae (110)

Bambusoideae – bamboos (1450)

Pooideae (3850)

Puelioideae (11)

Pharoideae (13)

Anomochlooideae (4)

Before 2005, fossil findings indicated that grasses evolved around 55 million years ago. Findings of grass-like phytoliths in Cretaceous dinosaur coprolites from the latest Cretaceous (Maastrichtian) aged Lameta Formation of India have pushed this date back to 66 million years ago. [11] [12] In 2011, revised dating of the origins of the rice tribe Oryzeae due to findings from the same deposit suggested a date as early as 107 to 129 Mya. [13]

Wu, You & Li (2018) described grass microfossils extracted from a specimen of the hadrosauroid dinosaur Equijubus normani from the Early Cretaceous (Albian) Zhonggou Formation (China), which were found to belong to primitive lineages within Poaceae, similar in position to the Anomochlooideae. The authors noted that India became separated from Antarctica, and therefore also all other continents, approximately at the beginning of late Aptian, so the presence of grasses in both India and China during the Cretaceous indicates that the ancestor of Indian grasses must have existed before late Aptian. Wu, You & Li considered the Barremian origin for grasses to be probable. [1]

The relationships among the three 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. [14] This separation occurred within the relatively short time span of about 4 million years.

According to Lester Charles King the spread of grasses in the Late Cenozoic would have changed patterns of hillslope evolution favouring slopes that are convex upslope and concave downslope and lacking a free face were common. King argued that this was the result of more slowly acting surface wash caused by carpets of grass which in turn would have resulted in relatively more soil creep. [15] [16]

Description

Diagram of a typical lawn grass plant.
Grassy grass plant.svg

Grasses may be annual or perennial herbs, [17] :10 generally with 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. [17] [18] Grass leaves are nearly always alternate and distichous (in one plane), and have parallel veins. [17] :11 Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins. [17] :11 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. [17] :11

Inflorecence scheme and floral diagram. 1 - glume, 2 - lemma, 3 - awn, 4 - palea, 5 - lodicules, 6 - stamens, 7 - ovary, 8 - styles. Grassbluete numbers clones unlinked.svg
Inflorecence scheme and floral diagram. 1 – glume, 2 – lemma, 3 – awn, 4 – palea, 5 – lodicules, 6 – stamens, 7 – ovary, 8 – styles.

Flowers of Poaceae are characteristically arranged in spikelets, each having one or more florets. [17] :12 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. [17] :13 A floret consists of the flower surrounded by two bracts, one external—the lemma—and one internal—the palea. The flowers are usually hermaphroditicmaize being an important exception—and mainly anemophilous or wind-pollinated, although insects occasionally play a role. [19] The perianth is reduced to two scales, called lodicules , [17] :11 that expand and contract to spread the lemma and palea; these are generally interpreted to be modified sepals. The fruit of grasses is a caryopsis, in which the seed coat is fused to the fruit wall. [17] :16 A tiller is a leafy shoot other than the first shoot produced from the seed. [17] :11

Growth and development

Grass flowers Grassflowers.jpg
Grass flowers

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. [20] :113–114

Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), stoloniferous, and rhizomatous.[ citation needed ] The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. There are both C3 and C4 grasses, referring to the photosynthetic pathway 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.

The C3 grasses are referred to as "cool-season" grasses, while the C4 plants are considered "warm-season" grasses. [17] :18–19

Although the C4 species are all in the PACMAD clade (see diagram above), it seems that various forms of C4 have arisen some twenty or more times, in various subfamilies or genera. In the Aristida genus for example, one species (A. longifolia) is C3 but the approximately 300 other species are C4. As another example, the whole tribe of Andropogoneae, which includes maize, sorghum, sugar cane, "Job's tears", and bluestem grasses, is C4. [10]

Distribution

The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent, [21] [22] including Antarctica with the presence of Antarctic hair grass on the Antarctic Peninsula.

Ecology

A kangaroo eating grass Kangur.rudy.drs.jpg
A kangaroo eating grass
Wind-blown grass in the Valles Caldera in New Mexico Grasses in the Valles Caldera 2014-06-26.JPG
Wind-blown grass in the Valles Caldera in New Mexico

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.[ citation needed ] Grass-dominated biomes are called grasslands. If only large, contiguous areas of grasslands are counted, these biomes cover 31% of the planet's land. [23] Grasslands include pampas, steppes, and prairies. [24] Grasses provide food to many grazing mammals—such as livestock, deer, and elephants—as well as to many species of butterflies and moths.[ citation needed ] 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 near the bottom of the plant; hence, grasses can quickly recover from cropping at the top. [25] 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 outcompete most grasses. Trampling grazers kill seedling trees but not grasses. [20] :137

Taxonomy

There are about 12,000 grass species in about 771 genera that are classified into 12 subfamilies. [26] See the full list of Poaceae genera.

Setaria verticillata from Panicoideae Setaria verticillata W IMG 1085.jpg
Setaria verticillata from Panicoideae
Tragus roxburghii from Chloridoideae Tragus roxburghii W IMG 1725.jpg
Tragus roxburghii from Chloridoideae

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 animals 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, floor matting, sports turf and baskets.

GrazingCowsPasture.jpg
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). Of all crops grown, 70% are grasses. [27] Three cereals rice, wheat, and maize (corn)provide more than half of all calories consumed by humans. [28] Cereals constitute the major source of carbohydrates for humans and perhaps the major source of protein, including rice (in southern and eastern Asia), 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 of sugarcane include sprouted grain, shoots, and rhizomes, and in drink they include sugarcane juice and plant milk, as well as rum, beer, whisky, and vodka.

Bamboo shoots are used in numerous Asian dishes and broths, and are available in supermarkets in various sliced forms, in both fresh, fermented and canned versions.

Lemongrass is a grass used as a culinary herb for its citrus-like flavor and scent.

Many species of grass are grown as pasture for foraging or as fodder for prescribed livestock feeds, particularly in the case of cattle, horses, and sheep. Such grasses may be cut and stored for later feeding, especially for the winter, in the form of bales of hay or straw, or in silos as silage. Straw (and sometimes hay) may also be used as bedding for animals.

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 such as Oriented structural straw board. Grass fiber can be used for making paper, and for biofuel production.[ citation needed ] Bamboo scaffolding is able to withstand typhoon-force winds that would break steel scaffolding. [23] 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.[ citation needed ]

Phragmites australis (common reed) is important for thatching and grass roots stabilize the sod of sod houses.[ citation needed ] Reeds are used in water treatment systems, in wetland conservation and land reclamation in Afro-Eurasia.[ citation needed ] Marram grass (Ammophila arenaria)

Lawn and ornamental use

A lawn in front of a building South Lawn.jpg
A lawn in front of a building

Grasses are the primary plant used in lawns, which themselves derive from grazed grasslands in Europe.[ citation needed ] They also provide an important means of erosion control (e.g., along roadsides), especially on sloping land.[ citation needed ] Grass lawns are an important covering of playing surfaces in many sports, including football (soccer), American football, tennis, golf, cricket, softball and baseball.

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.[ citation needed ]

Sports turf

Forms of grass are used to cover baseball fields, like this one in Citi Field, home of the New York Mets. Citi Field Day.jpg
Forms of grass are used to cover baseball fields, like this one in Citi Field, home of the New York Mets.

Grass playing fields, courses and pitches are the traditional playing surfaces for many sports, including American football, association football, baseball, cricket, golf, and rugby. Grass surfaces are also sometimes used for horse racing and tennis. Type of maintenance and species of grass used may be important factors for some sports, less critical for others. 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. [29]

Cricket

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. Australia vs India.jpg
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.

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. [30]

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.[ citation needed ]

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.[ citation needed ] 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.[ citation needed ] Among the world's most prestigious court for grass tennis is Centre Court at Wimbledon, London which hosts the final of the annual Wimbledon Championships in England, one of the four Grand Slam tournaments.

Economically important grasses

Grain crops
Leaf and stem crops
Lawn grasses
Ornamental grasses (Horticultural)
Model organisms

Role in society

Grass-covered house in Iceland Grass covered house in Iceland 1972.jpg
Grass-covered house in Iceland
Typical grass seen in meadows Grass Blades.jpg
Typical grass seen in meadows

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.[ citation needed ]

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:

...the desire for upward mobility and its manifestation in the lawn. As Virginia Jenkins, author of The Lawn, put it quite bluntly, 'Upper middle-class Americans emulated aristocratic society with their own small, semi-rural estates.' In general, the lawn was one of the primary selling points of these new suburban homes, as it shifted social class designations from the equity and ubiquity of urban homes connected to the streets with the upper-middle class designation of a "healthy" green space and the status symbol that is the front lawn. [31] [32]

Many US 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. [33]

The smell of the freshly cut grass is produced mainly by cis-3-Hexenal. [34]

Some common aphorisms involve grass. For example:

A folk myth about grass is that it refuses to grow where any violent death has occurred. [35]

See also

Related Research Articles

Flowering plant The clade of seed plants that produce flowers

The flowering plants, also known as Angiospermae, or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species. Like gymnosperms, angiosperms are seed-producing plants. They are distinguished from gymnosperms by characteristics including flowers, endosperm within their seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure; in other words, a fruiting plant. The term comes from the Greek words angeion and sperma ("seed").

Poales Order of monocotyledonous flowering plants

The Poales are a large order of flowering plants in the monocotyledons, and includes families of plants such as the grasses, bromeliads, and sedges. Sixteen plant families are currently recognized by botanists to be part of Poales.

<i>Poa pratensis</i> Species of plant

Poa pratensis, commonly known as Kentucky bluegrass, smooth meadow-grass, or common meadow-grass, is a perennial species of grass native to practically all of Europe, North Asia and the mountains of Algeria and Morocco. Although the species is spread over all of the cool, humid parts of the United States, it is not native to North America. The Spanish Empire brought the seeds of Kentucky bluegrass to the New World in mixtures with other grasses. Poa pratensis forms a valuable pasture plant, characteristic of well-drained, fertile soil. It is also used for making lawns in parks and gardens and is common in cool moist climates like the Pacific Northwest, and Northeastern United States. When found on native grasslands in Canada, however, it is considered an unwelcome exotic plant, and is indicative of a disturbed and degraded landscape.

Andropogoneae

The Andropogoneae, sometimes called the sorghum tribe, are a large tribe of grasses (family Poaceae) with roughly 1,200 species in 90 genera, mainly distributed in tropical and subtropical areas. They include such important crops as maize (corn), sugarcane, and sorghum. All species in this tribe use C4 carbon fixation, which makes them competitive under warm, high-light conditions.

<i>Poa</i> genus of flowering plants in the grass family Poaceae

Poa is a genus of about 500 species of grasses, native to the temperate regions of both hemispheres. Common names include meadow-grass, bluegrass, tussock, and speargrass. Poa (πόα) is Greek for "fodder". Poa are members of the subfamily Pooideae of the family Poaceae.

Pooideae

The Pooideae are the largest subfamily of the grass family Poaceae, with about 4,000 species in 15 tribes and roughly 200 genera. They include some major cereals such as wheat, barley, oat, rye and many lawn and pasture grasses. They are often referred to as cool-season grasses, because they are distributed in temperate climates. All of them use the C3 photosynthetic pathway.

Panicoideae

Panicoideae is the second-largest subfamily of the grasses with over 3,500 species, mainly distributed in warm temperate and tropical regions. It comprises some important agricultural crops, including sugarcane, maize, sorghum, and switchgrass.

Agrostology Scientific study of the grasses

Agrostology, sometimes graminology, is the scientific study of the grasses. The grasslike species of the sedge family (Cyperaceae), the rush family (Juncaceae), and the bulrush or cattail family (Typhaceae) are often included with the true grasses in the category of graminoid, although strictly speaking these are not included within the study of agrostology. In contrast to the word graminoid, the words gramineous and graminaceous are normally used to mean "of, or relating to, the true grasses (Poaceae)".

<i>Brachyelytrum</i>

Brachyelytrum is a genus of North American and East Asian plants in the grass family, classified in its own tribe Brachyelytreae.

Awn (botany)


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.

<i>Rinconsaurus</i>

Rinconsaurus is a genus of titanosaur sauropod dinosaur from the Late Cretaceous in what is now Argentina. The type species, Rinconsaurus caudamirus, was described by Calvo and Riga in 2003, and is based on three partial skeletons.

<i>Lolium perenne</i> Species of plant

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.

<i>Cynosurus cristatus</i>

Cynosurus cristatus, the crested dog's-tail, is a short-lived perennial grass in the family Poaceae, characterised by a seed head that is flat on one side. It typically grows in species rich grassland. It thrives in a variety of soil types but avoids the acid and calcareous extremes of pH, and prefers well drained soils. It may be grown as an ornamental plant.

Tussock (grass)

Tussock grasses or bunch grasses are a group of grass species in the family Poaceae. They usually grow as singular plants in clumps, tufts, hummocks, or bunches, rather than forming a sod or lawn, in meadows, grasslands, and prairies. As perennial plants, most species live more than one season. Tussock grasses are often found as forage in pastures and ornamental grasses in gardens.

Stipeae

The Stipeae are a tribe of grasses within the subfamily Pooidae, with up to 600 described species.

BOP clade Clade of grasses

The BOP clade (sometimes BEP clade) is one of two major lineages (or clades) of undefined taxonomic rank in the grasses (Poaceae), containing more than 5,400 species, about half of all grasses. Its sister group is the PACMAD clade; contrary to many species of that group who have evolved C4 photosynthesis, the BOP grasses all use the C3 photosynthetic pathway.

Thomas Robert Soderstrom

Thomas Robert Soderstrom was an American agrostologist His special field of study was the grass family Gramineae or Poaceae. He was Curator of Grasses at the National Museum of Natural History in Washington, DC for some twenty years.

<i>Ischaemum rugosum</i>

Ischaemum rugosum, also known as saramollagrass, is a flowering plant belonging to the grass family Poaceae in the genus Ischaemum, and is native to tropical and temperate regions of Asia, growing in marshes and other wet habitats. It is a vigorous annual, and is an invasive species in South America and Madagascar. It reaches heights of up to 1 m and is primarily recognized by the ridged surface of its sessile spikelet’s lower glume. Despite its historic importance as fodder in Asia, the grass has become a major weed in mid-latitude rice paddies throughout Asia and South America.

<i>Rottboellia cochinchinensis</i>

Rottboellia cochinchinensis is a species of grass known by the common names Itchgrass,Raoul grass, corngrass, Kokoma grass, Guinea-fowl grass, jointed grass, Shamwa grass and Kelly grass. It is a tall, tufted annual grass whose stems (culms) grow up to 300 cm in height with leaf-blades of up to 45 cm in length. The species flowers at the apex of culms in the form of spike-like racemes composed of paired spikelets. The common name Itchgrass comes from the bristly (hispid) leaf-sheath which can be irritating to the skin.

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