Asisbiz photo collection of ‘Grasses’.
Poaceae or Gramineae is a family in the Class Liliopsida (the monocots) of the flowering plants. Plants of this family are usually called grasses, or, to distinguish them from other graminoids, true grasses; the shrub- or tree-like plants in this family are called bamboo (there are also herbaceous, non-woody bamboos). There are about 600 genera and some 9,000–10,000 or more species of grasses (Kew Index of World Grass Species).
Plant communities dominated by Poaceae are called grasslands; it is estimated that grasslands comprise 20% of the vegetation cover of the earth. Grass species also occur in many other habitats that are not formally considered to be grasslands, including different types of wetlands (e.g., fens, marshes), forests and tundra.
Poaceae is 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 man's ability to domesticate cereal grass crops around the world.
The term "grass" is also applied (incorrectly) to many grass-like plants that are not members of the Poaceae lineage, including the rushes (Juncaceae) and sedges (Cyperaceae). This broad and general use of the word ‘grass’ has lead to plants of the Poaceae often being called "true grasses".
Structure and growth
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.
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". All grasses can be annual or perennial.
* Annual Cool Season - wheat, rye, Annual Bluegrass, and oats
Subfamilies and genera
* Anomochlooideae, a small lineage of broad-leaved grasses that includes two genera (Anomochloa, Streptochaeta)
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 carbohydrate 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 food, particularly for sheep and cattle. Some other grasses are of major importance for foliage production, thereby indirectly providing more human calories.
Grass fibre 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 the Old World.
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.
Economically important grasses
Leaf and stem crops
* Bahia grass
* Brachypodium distachyon
Biomes dominated by grasses are called grasslands. If only large contiguous chunks 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; see List of Lepidoptera that feed on grasses.
The evolution of large grazing animals in the Cenozoic has contributed to the spread or 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.
Grass and society
Some common aphorisms involve grass. For example:
* "The grass is always greener on the other side" suggests that an alternate state of affairs will always seem preferable to one's own.
This webpage was updated on 27th October 2010
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