Poaceae  

The Poaceae (also called Gramineae or true grasses) are a large and nearly ubiquitous family of monocotyledonous flowering plants. With more than 10,000 domesticated and wild species, the Poaceae are the fifth-largest plant family, following the Asteraceae, Orchidaceae, Fabaceae, and Rubiaceae.^[3] Though 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.

Grasslands are estimated to constitute 20% of the vegetation cover of the Earth. Poaceae live in many other habitats, including wetlands, forests, and tundra.

Domestication of poaceous cereal crops such as maize (corn), wheat, rice, barley, and millet lies at the foundation of sedentary living and civilization around the world, and the Poaceae still constitute the most economically important plant family in modern times, providing forage, building materials (bamboo, thatch) and fuel (ethanol), as well as food.

Description[edit]

Diagram of a typical lawn grass plant.

Grasses generally have the following characteristics (the image gallery can be used for reference):

Poaceae have hollow stems called culms plugged at intervals by solid leaf-bearing nodes. 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.

Parts of a spikelet

Flowers of Poaceae 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, 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 Poaceae 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 flowers

Growth and development[edit]

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.^[4]

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 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 annua), 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.

Ecology[edit]

Grass-dominated biomes are called grasslands. If only large, contiguous areas of grasslands are counted, these biomes cover 31% of the planet's land.^[5] 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.

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.^[6]

Evolution[edit]

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.^[1][8] Indeed, revised dating of the origins of the rice tribe Oryzeae suggest a date as early as 107 to 129 Mya.^[9]

The relationships among the subfamilies Bambusoideae, Ehrhartoideae and Pooideae in the BEP clade have been resolved: Bambusoideae and Pooideae are more closely related to each other than to Ehrhartoideae.^[10] This separation occurred within a relatively short time span (about 4 million years).

Distribution[edit]

The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent,^[11] and are absent only from central Greenland and much of Antarctica.^[12]

Taxonomy[edit]

Setaria verticillata from Panicoideae

Tragus roxburghii from Chloridoideae

Recent classifications of the grass family^[13] recognize 12 subfamilies and a small number of taxa with uncertain placements:

• Anomochlooideae 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

Depending on the classification followed, the family includes around 668 genera.^[3]

Etymology[edit]

The Poaceae name was given by John Hendley Barnhart in 1895,^[14] based on the tribe Poeae (described in 1814 by Robert Brown), and the type genus Poa (described in 1753 by Linnaeus). The term is derived from the Ancient Greek term for grass.

Uses[edit]

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.

Food production[edit]

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.^[15] Of all crops, 70% are grasses.^[16] Cereals constitute the major source of carbohydrates for humans and perhaps the major source of protein, and include 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. Many other grasses are grown for forage and fodder for animal feed, particularly for sheep and cattle, thereby indirectly providing more human calories.

Industry[edit]

Grasses are used for construction. Scaffolding made from bamboo is able to withstand typhoon-force winds that would break steel scaffolding.^[5] 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 fiber can be used for making paper, and for biofuel production.

Phragmites australis (common reed) is important in water treatment, wetland habitat preservation and land reclamation in Afro-Eurasia.

Lawn and ornamental grasses[edit]

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.

Although supplanted by artificial turf in some games, grasses are still an important covering of playing surfaces in many sports, including football (soccer), 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, and slope stabilization. They are often used in natural landscaping, xeriscaping, contemporary or modern landscaping, wildlife gardening, and native plant gardening.

Economically important grasses[edit]

Grasses and society[edit]

Grass-covered house in Iceland

Grasses have long had significance in human society. They have been cultivated as feed for domesticated animals for up to 10,000 years, and have been used to make paper since the second century AD.^{[citation needed]} Also, 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]}

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.^[17]

Genera[edit]

See the full list of Poaceae genera.

Image gallery[edit]

• 

  Leaves of Poa trivialis showing the ligules

• 

  Bamboo stem and leaves, nodes are evident

• 

  A Chasmanthium latifolium spikelet

• 

  Wheat spike and spikelet

• 

  Spikelet opened to show caryopsis

• 

  Harestail grass

• 

  Grass

• 

  Sugarcane (Saccharum officinarum)

• 

  Roots of Bromus hordeaceus

• 

  Barley mature spikes (Hordeum vulgare)

• 

  Illustration depicting both staminate and pistillate flowers of maize (Zea mays)

• 

  A grass flower head (meadow foxtail) showing the plain-coloured flowers with large anthers.

• 

  Anthers detached from a meadow foxtail flower

• 

  Setaria verticillata, bristly foxtail

• 

  Setaria verticillata, bristly foxtail

• 

  Oryza sativa, Kerala, India

See also[edit]

• Agrostology
• Grass
• Bunch grass
• Ornamental grass
• Sedges
• Rushes
• PACMAD clade

References[edit]

A cereal is a grass, a member of the monocot family Poaceae,^[1] cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grains are grown in greater quantities and provide more food energy worldwide than any other type of crop;^{[citation needed]} they are therefore staple crops.

In their natural form (as in whole grain), they are a rich source of vitamins, minerals, carbohydrates, fats, oils, and protein. When refined by the removal of the bran and germ, the remaining endosperm is mostly carbohydrate. In some developing nations, grain in the form of rice, wheat, millet, or maize constitutes a majority of daily sustenance. In developed nations, cereal consumption is moderate and varied but still substantial.

The word cereal derives from Ceres, the name of the Roman goddess of harvest and agriculture.

History[edit]

This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2012)

The first cereal grains were domesticated about 8,000 years ago by ancient farming communities in the Fertile Crescent region. Emmer wheat, einkorn wheat, and barley were three of the so-called Neolithic founder crops in the development of agriculture. Around the same time, millets and rices were starting to become domesticated in east Asia. Sorghum and millets were also being domesticated in sub-Saharan West Africa.

Production[edit]

The following table shows the annual production of cereals in 1961,^[2] 2010, 2011, 2012, and 2013 ranked by 2013 production.^[3] All but buckwheat and quinoa are true grasses (these two are pseudocereals).

Maize, wheat, and rice together accounted for 89% of all cereal production worldwide in 2012, and 43% of all food calories in 2009,^[3] while the production of oats and triticale have drastically fallen from their 1960s levels. Other grains that are important in some places, but that have little production globally (and are not included in FAO statistics), include:

• Teff, an ancient grain that is a staple in Ethiopia. It is high in fiber and protein. Its flour is often used to make injera. It can also be eaten as a warm breakfast cereal similar to farina with a chocolate or nutty flavor. Its flour and whole grain products can usually be found in natural foods stores.
• Wild rice, grown in small amounts in North America.
• Amaranth, an ancient pseudocereal, formerly a staple crop of the Aztec Empire and now widely grown in Africa.
• Kañiwa, close relative of quinoa.

Several other species of wheat have also been domesticated, some very early in the history of agriculture:

• Spelt, a close relative of common wheat.
• Einkorn, a wheat species with a single grain.
• Emmer, one of the first crops domesticated in the Fertile Crescent.
• Durum, the only tetraploid species of wheat currently cultivated, used to make semolina.
• Kamut, an ancient relative of durum with an unknown history.

In 2013 global cereal production reached a record 2,521 million tonnes. A slight dip to 2,498 million tonnes was forecast for 2014 by the FAO in July 2014.

Farming[edit]

A wheat field in Dorset, England

While each individual species has its own peculiarities, the cultivation of all cereal crops is similar. Most are annual plants; consequently one planting yields one harvest. Wheat, rye, triticale, oats, barley, and spelt are the "cool-season" cereals.^{[citation needed]} These are hardy plants that grow well in moderate weather and cease to grow in hot weather (approximately 30 °C, but this varies by species and variety). The "warm-season" cereals are tender and prefer hot weather. Barley and rye are the hardiest cereals, able to overwinter in the subarctic and Siberia. Many cool-season cereals are grown in the tropics. However, some are only grown in cooler highlands, where it may be possible to grow multiple crops in a year.

For a few decades, there has also been increasing interest in perennial grain plants. This interest developed due to advantages in erosion control, reduced need of fertiliser, and potential lowered costs to the farmer. Though research is still in early stages, The Land Institute in Salina, Kansas has been able to create a few cultivars that produce a fairly good crop yield.^[6]

Planting[edit]

Cereal grain seeds from left to right: wheat, spelt, barley, oat.

The warm-season cereals are grown in tropical lowlands year-round and in temperate climates during the frost-free season. Rice is commonly grown in flooded fields, though some strains are grown on dry land. Other warm climate cereals, such as sorghum, are adapted to arid conditions.

Cool-season cereals are well-adapted to temperate climates. Most varieties of a particular species are either winter or spring types. Winter varieties are sown in the autumn, germinate and grow vegetatively, then become dormant during winter. They resume growing in the springtime and mature in late spring or early summer. This cultivation system makes optimal use of water and frees the land for another crop early in the growing season.

Winter varieties do not flower until springtime because they require vernalization: exposure to low temperatures for a genetically determined length of time. Where winters are too warm for vernalization or exceed the hardiness of the crop (which varies by species and variety), farmers grow spring varieties. Spring cereals are planted in early springtime and mature later that same summer, without vernalization. Spring cereals typically require more irrigation and yield less than winter cereals.

Period[edit]

Threshing; Tacuinum Sanitatis, 14th century

Once the cereal plants have grown their seeds, they have completed their life cycle. The plants die and become brown and dry. As soon as the parent plants and their seed kernels are reasonably dry, harvest can begin.

In developed countries, cereal crops are universally machine-harvested, typically using a combine harvester, which cuts, threshes, and winnows the grain during a single pass across the field. In developing countries, a variety of harvesting methods are in use, depending on the cost of labor, from combines to hand tools such as the scythe or cradle.

If a crop is harvested during wet weather, the grain may not dry adequately in the field to prevent spoilage during its storage. In this case, the grain is sent to a dehydrating facility, where artificial heat dries it.

In North America, farmers commonly deliver their newly harvested grain to a grain elevator, a large storage facility that consolidates the crops of many farmers. The farmer may sell the grain at the time of delivery or maintain ownership of a share of grain in the pool for later sale. Storage facilities should be protected from small grain pests, rodents and birds.

Nutritional facts[edit]

Some grains are deficient in the essential amino acid lysine. That is why many vegetarian cultures, in order to get a balanced diet, combine their diet of grains with legumes. Many legumes, on the other hand, are deficient in the essential amino acid methionine, which grains contain. Thus, a combination of legumes with grains forms a well-balanced diet for vegetarians. Common examples of such combinations are dal (lentils) with rice by South Indians and Bengalis, dal with wheat in Pakistan and North India, and beans with corn tortillas, tofu with rice, and peanut butter with wheat bread (as sandwiches) in several other cultures, including Americans.^[7] The amount of crude protein found in grain is measured as the grain crude protein concentration.^[8]

Standardization[edit]

The ISO has published a series of standards regarding cereal products which are covered by ICS 67.060.^[9]

See also[edit]

Food portal

References[edit]