POACEAE OR GRAMINEAE
Scientific classification
Kingdom:
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Plantae
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Phylum:
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Angiosperms
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Class:
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Monocots
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Order:
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Family:
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Poa L.
=Poaceae Barnhart
=Gramineae
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Subfamilies:
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There are 12 subfamilies
Subfamily Anomochlooideae
Subfamily Pharoideae Subfamily Puelioideae Subfamily Bambusoideae Subfamily Pooideae Subfamily Ehrhartoideae Subfamily Arundinoideae Subfamily Centothecoideae Subfamily Chloridoideae Subfamily Panicoideae Subfamily Danthonioideae Subfamily Micrairoideae |
The Poaceae (also known as the Gramineae) is a large and
nearly ubiquitous family of monocot flowering plants (Monocotyledons). A
monocotyledo-nous family containing the grasses, which number about over 10,000 species in
about 800 genera.
Grasses
generally have long narrow parallel-veined leaves inserted distichously on a
round hollow stem. The inconspicuous flowers are usually borne in a terminal
panicle, spike, or raceme consisting of a number of spikelets. Each flower is
surrounded by two bracts. The fruit is a *caryopsis.
Members of this family are commonly
called grasses, although the term (land) "grass" is also
applied to plants that are not in the Poaceae lineage.
The word "grass" has led to
plants of the Poaceae often being called "true grasses". Plant communities dominated by Poaceae are
called grasslands;
grasslands are estimated to comprise 20% of the vegetation cover of the Earth.
With about 10,025 currently accepted species in about 668 genera, the Poaceae represent the fifth largest plant
family.
Economically
they are the most important family of plants as they contain all the cereals,
which are man's staple diet. Wheats (Triticum), maize (Zea mays), rice (Oryza
saliva), barley (Hordeum vulgare), oats (Avena sativa), rye (Secale cereale),
sugar cane (Saccharum officinarum), and sorghums (Sorghum) are all grasses.
Poaceae are often considered to be the
most important of all plant families to human economies: it includes the staple food grains
and cereal crops grown around the world, lawn and
forage grasses, and bamboo, which
is widely used for construction throughout east
Asia and sub-Saharan Africa .
Civilization was founded largely on the ability to domesticate cereal grass
crops around the world.
Description
Grasses generally have the following characteristics:
Poaceae have hollow stems called culms,
which are plugged (solid) at intervals called nodes, the points along the culm
at which leaves arise. Grass leaves are
alternate, distichous (in one plane) or rarely spiral, and parallel-veined.
Each leaf is differentiated into a lower sheath, which hugs the stem for a
distance and a blade with margins usually entire.
-Leaf of Poaceae are
hardened with silica phytoliths,
which helps discourage grazing animals. In some grasses (such as sword
grass), this makes the edges of 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.
-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 called the lemma (the
external one) and the palea (the
internal). The flowers are usually hermaphroditic (maize,
monoecious, is an exception) and pollination is
always anemophilous,
that is, by wind. 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) spike.
-The fruit of
Poaceae is a caryopsis,
in which the seed coat is fused to the fruit wall and thus, not separable from
it (as in a maize kernel). A tiller a non-seed leaf shoot.
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 that particularly adapts them to hot climates and an atmosphere low in carbon
dioxide.
C3 grasses are referred to as
"cool season" grasses, while C4 plants are considered "warm
season" grasses; they may be either annual or perennial.
-Perennial cool season - orchardgrass
(cocksfoot, Dactylis glomerata), fescue (Festuca spp), Kentucky bluegrass and perennial ryegrass (Lolium perenne).
-Annual warm season - corn, sudangrass, and pearl millet.
-Perennial warm season - big bluestem, indiangrass, bermudagrass and
switchgrass.
Ecology
Biomes dominated by grasses are called grasslands.
If only large contiguous areas 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.
In addition to their use as forage worldwide by
many grazing mammals, such as cattle and other livestock, deer, and elephants,
grasses are used as food plants by many species of butterflies and moths.
The evolution of large grazing animals in the Cenozoic has
contributed to the spread of 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 their lack of woody stems helps them to resist
the damage of trampling.
Evolution
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 phytolith sresembling
grass phytoliths (including ancestors of rice and bamboo) in Cretaceous dinosaur coprolites,
may place the diversification of grasses to an earlier date. Indeed, revised
dating of the origins of the rice tribe Oryzeae have
been led to the suggestion that the date might be pushed back as early as 107
Ma to 129 Ma.
The relationships among the
subfamilies Bambusoideae, Ehrhartoideae and
Pooideae in the BEP
clade have been resolved: Bambusoideae and Pooideae are more closely related
than Ehrhartoideae. This separation occurred within a relatively short time
span (~4 million years).
Distribution
The grass family is one of the most widely
distributed and abundant groups of plants on Earth. They are found on every
continent, and are essentially only absent from central Greenland and
much of Antarctica.
Taxonomy
The most recent classification of the grass family
recognizes 12 subfamilies:
1-Anomochlooideae, a
small lineage of broad-leaved grasses that includes two genera (Anomochloa, Streptochaeta).
2-Pharoideae, a small
lineage of grasses that includes three genera, including Pharus and Leptaspis.
3-Puelioideae, a small
lineage that includes the African genus Puelia.
4-Pooideae, including wheat, barley, oats, brome-grass (Bromus),
reed-grasses (Calamagrostis) and many lawn and pasture grasses.
5-Bambusoideae,
including bamboo.
6-Ehrhartoideae, including rice, wild rice.
7-Arundinoideae,
including giant reed, common reed.
8-Centothecoideae, a
small subfamily of 11 genera that is sometimes included in Panicoideae.
9-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).
10-Panicoideae,
including panic grass, maize, sorghum, sugarcane, most millets, fonio, and bluestem
grasses.
11-Micrairoideae.
12-Danthonioideae, including pampas grass.
Depending on the classification followed, the
family includes approximately 668 genera.
Etymology
The Poaceae was named 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 byLinnaeus).
The term is derived from the Ancient Greek term for "grass".
Uses
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
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. 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
Asia, maize in Central andSouth 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
-Grasses are used for construction. 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, 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.
Phragmites
australis (common reed) is important in water treatment,
wetland habitat preservation and land reclamation in Afro-Eurasia.
Lawn and ornamental grasses
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, tennis, golf, cricket,
and softball/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.
Econumically important grasses
Economically
important grasses:
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Leaf and
stem crops
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Maize (Corn)
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Cortaderia spp.
Deschampsia spp.
Melica spp.
Stipa spp.
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Maize (Corn)
Rice
Sorghum
Wheat
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Grasses and society
Grasses have long had significance in human
society. They have been cultivated as a food source for domesticated animals for
up to 10,000 years, and have been used to make paper since
the second century AD. 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.
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.
Preferences:
4-Poaceae - Definition and More from the
Free Merriam-Webster ... www.merriam-webster.com/dictionary/poaceae .
5-Poaceae (Gramineae) - Flowering Plant
Families, UH Botany www.botany.hawaii.edu/faculty/carr/po.htm .
The information here has been very helpful
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