Poaceae

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Grasses
)
"Grass" redirects here. For other uses, see Grass (disambiguation).
"Gramineae" redirects here. Not to be confused with Graminea.

Grasses
Temporal range: Albian–Present [1]
Flowering head of meadow foxtail (Alopecurus pratensis), with stamens exerted at anthesis
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Clade: Graminid clade
Family: Poaceae
Barnhart[2]
Type genus
Poa
Subfamilies
Synonyms[3]

Gramineae 

Juss.

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

With around 780

Orchidaceae, Fabaceae and Rubiaceae.[5]

The Poaceae are the most economically important plant family, providing

thatch, and straw); others can provide a source of biofuel, primarily via the conversion of maize to ethanol
.

Grasses have

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.

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", groups such as the

monocot
group of plants.

Description

Grasses may be

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.[8]
: 11 

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

lodicules,[8]: 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.[8]
: 16  A tiller is a leafy shoot other than the first shoot produced from the seed.[8]: 11 

Growth and development

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

mown regularly without severe damage to the plant.[11]
: 113–114 

Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), stoloniferous, and rhizomatous.[12] The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. There are both

water use efficiency, rendering them better adapted to hot, arid environments.[13]

The C3 grasses are referred to as "cool-season" grasses, while the C4 plants are considered "warm-season" grasses.[8]: 18–19 

Although the C4 species are all in the

sugar cane, "Job's tears", and bluestem grasses, is C4.[14] Around 46 percent of grass species are C4 plants.[15]

Taxonomy

The name Poaceae was given 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

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.

A cladogram shows subfamilies and approximate species numbers in brackets:[14]

PACMAD clade

Aristidoideae
(350)

BOP clade

Oryzoideae (110)

Bambusoideae
– bamboos (1450)

Pooideae (3850)

Puelioideae (11)

Pharoideae (13)

Anomochlooideae (4)

Anomochloa marantoidea
, one of the most primitive living grass species

Before 2005, fossil findings indicated that grasses evolved around 55 million years ago. Finds 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.[18][19] In 2011, fossils from the same deposit were found to belong to the modern rice tribe Oryzeae, suggesting substantial diversification of major lineages by this time.[20]

In 2018, a study described grass microfossils extracted from the teeth of the hadrosauroid dinosaur Equijubus normani from northern China, dating to the Albian stage of the Early Cretaceous approximately 113–100 million years ago, which were found to belong to primitive lineages within Poaceae, similar in position to the Anomochlooideae. These are currently the oldest known grass fossils.[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.[21] 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.[22][23]

Subdivisions

There are about 12,000 grass species in about 771 genera that are classified into 12 subfamilies.[24] See the full list of Poaceae genera.

Setaria verticillata from Panicoideae

Distribution

The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent,[25][26] including Antarctica. The Antarctic hair grass, Deschampsia antarctica is one of only two plant species native to the western Antarctic Peninsula.

Ecology

Wind-blown grass in the Valles Caldera in New Mexico, United States

Grasses are the

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.[27] Grasslands include pampas, steppes, and prairies.[28] Grasses provide food to many grazing mammals,[29] as well as to many species of butterflies and moths.[30][31] Many types of animals eat grass as their main source of food, and are called
brown butterflies. Grasses are also eaten by omnivorous or even occasionally by primarily carnivorous
animals.

A kangaroo eating grass

Grasses dominate certain biomes, especially temperate grasslands, because many species are adapted to grazing and fire.[32]

Grasses are unusual in that the meristem is near the bottom of the plant; hence, grasses can quickly recover from cropping at the top.[33] 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.[11]: 137 

Uses

Grasses are, in human terms, perhaps the most economically important plant family.

matting, sports turf and baskets
.

Grazing cattle on a pasture near Hradec nad Moravicí in Czech Silesia.

Food production

Of all crops grown, 70% are grasses.

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.

An example of a sod-forming perennial grass used in agriculture is Thinopyrum intermedium.

Industry

Grasses are used as raw material for a multitude of purposes, including construction and in the composition of building materials such as

Bamboo scaffolding is able to withstand typhoon-force winds that would break steel scaffolding.[27] 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.[39]

Phragmites australis (common reed) is important for thatching and wall construction of homes in Africa.[40] Grasses are used in water treatment systems,[41] in wetland conservation and land reclamation, and used to lessen the erosional impact of urban storm water runoff.[42]

Palaeoecological reconstructions

Processed, fossilised pollen from the family Poaceae. Species unknown.

domesticated grasses from wild ones,[46][47][48] and to indicate various biological features like how they perform photosynthesis,[49] their breeding systems,[49][50] and genetic complexity.[51][52][44] Yet, there's ongoing debate about how effective pollen size is for piecing together historical landscapes and weather patterns, considering other factors such as genetic material amount might also affect pollen size.[53][54][44] Despite these challenges, new techniques in Fourier-Transform Infrared Spectroscopy (FT-IR) and improved statistical methods are now helping to better identify these similar-looking pollen types.[45]

Lawn and ornamental use

Main articles: Lawn and Ornamental grass
A lawn in front of a building

Grasses are the primary plants used in lawns, which themselves derive from grazed

football (soccer), American football, tennis, golf, cricket, softball and baseball
.

Ornamental grasses, such as

native plant gardening.[citation needed] They are used as screens and hedges.[55]

Sports turf

See also:
Sports turf, Turf management, and Sand-based athletic fields

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.[56]

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.
Main article: Cricket pitch § Preparation and maintenance of the playing area

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.[57]

Golf

Main article: Golf course

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 turf grass varieties.[58]

Tennis

Main article: Grass court

In tennis, grass is grown on very hard-packed soil, and the bounce of a

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

A number of grasses are invasive species that damage natural ecosystems, including forms of Phragmites australis which are native to Eurasia but has spread around the world.[59][60]


Role in society

Grass-covered house in Iceland
Typical grass seen in meadows
Grass with non-grass flowers around it

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.[61]

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.[62][63]

In communities with drought problems, watering of lawns may be restricted to certain times of day or days of the week.[64] 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.[65][66]

The smell of freshly cut grass is produced mainly by cis-3-Hexenal.[67]

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.[68]

Image gallery

See also

References

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External links

Wikimedia Commons has media related to Poaceae and Grass.
Wikispecies has information related to Poaceae.
Look up grass in Wiktionary, the free dictionary.
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