The true grasses are monocotyledonous plants (Class Liliopsida) in the Family Poaceae, also known as Gramineae. There are about 600 genera and perhaps 10,000 species of grasses. It is estimated that grasslands comprise 20% of the vegetation cover of the earth. This family is the most important of all plant families to human economies, including lawn and forage grasses, the staple food grains grown around the world, and bamboo, widely used for construction throughout Asia.

Grasses generally have the following characteristics:

• Typically hollow stems (called culms), plugged at intervals (the nodes).
• Leaves, arising at nodes, alternate, distichous (in one plane) or rarely spiral, and parallel-veined.
• Leaves differentiated into a lower sheath hugging the stem for a distance and a blade with margin usually entire; a ligule (a membranous appendage or ring of hairs) lies at the junction between sheath and blade.
• Small, wind-pollinated flowers (called florets) sheathed inside two glumes (bracts), lacking petals, and grouped into spikelets, these arranged in a panicle, raceme, spike, or head.
• Fruit that is a caryopsis.
• The blades of many grasses are hardened with silica phytoliths, which helps discourage grazing animals. In some grasses (such as sword grass) this makes the grass blades sharp enough to cut human skin.
• Grass blades grow at the base of the blade and not from growing tips: this gives the grasses a competitive edge under pressure of grazing herbivores, as the growing points are less likely to be damaged.

The success of the grasses lies in part in their morphology and growth processes, and in part in their physiological diversity. The grasses divide into two physiological groups, using the C3 and C4 carbon fixation processes. The C4 grasses have a photosynthetic pathway linked to specialised leaf anatomy that particularly adapts them to hot climates.

Grass evolution

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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 phytoliths resembling grass phytoliths (including ancestors of rice and bamboo) in Cretaceous dinosaur coprolites (^*), may place the diversification of grasses to an earlier date.

The flowers of grass are reduced from the general monocotyledon type. The immediate ancestor of the first grass may have been a small Liliaceous plant with rhizomes and many small flowers, growing in dense patches, which changed over to wind pollination to get round limitations caused by shortage of insects to pollinate the flowers.

Cultivation and uses

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Agricultural grasses grown for seed for human food production are called cereals. Cereals constitute the major source of food energy 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. Some other grasses are of major importance for foliage production. 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.

Grasses are used for construction; 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 fibre can be used for making paper, and for biofuel production. Grasses are the primary plant used in lawns, which themselves derive from grazed grasslands in Europe. Phragmites australis is important in water treatment, wetland habitat preservation and land reclamation in the Old World.

Grasses are used as food plants by many species of butterflies and moths. see List of Lepidoptera which feed on grasses.

Economically important grasses

Grain crops

• Barley
• Maize
• Oats
• Rice
• Rye
• Sorghum              
• Wheat

Leaf and stem crops        

• Bamboo
• Marram grass
• Meadow-grass
• Reed
• Ryegrass
• Sugarcane

Lawn grasses

• Bahia grass
• Bent grass
• Bermuda grass    
• Fescue
• Meadow-grass
• Ryegrass
• Zoysia

Model organisms

• Brachypodium distachyon

Grass and society

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Grass has long had significance in human society. It has been cultivated as a food source for domesticated animals for up to 10,000 years, and has been used to make paper since at least as early as 2400 B.C. In modern suburbia, a well maintained grassy lawn is a sign of responsibility to the overall appearance of the neighborhood.

Some idioms evoke images of grass. For example:

• "The grass is always greener on the other side" suggests that the greenness of grass is a positive quality.
• "Don't let the grass grow under your feet" references the speed with which grass grows.
• "A snake in the grass" cautions about the dangers that may be hidden in the grass.

See also

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• agrostology
• grass
• sedges

External links and references

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• TurfFiles by North Carolina State University
• Kew Index of World Grass Species
• Definitions of Grass structures
• Poaceae in L. Watson and M. J. Dallwitz] (1992 onwards), The families of flowering plants.
• L. Watson and M. J. Dallwitz (1992 onwards). The grass genera of the world.
• Piperno, D. R. & Sues, H.-D. (2005). Paleontology: Dinosaurs Dined on Grass. Science 310 (5751): 1126-1128 (18 November 2005) summary. Poales | Plant families | Grasses | gardening | Gramínies | Lipnicovité | Græs-familien | Süßgräser | Poácea | Poacoj | Poaceae | Poaceae | דגניים | Migliniai augalai | Pázsitfűfélék | Grassenfamilie | イネ科 | Grasfamilien | Wiechlinowate | Poaceae | Злаки | Heinäkasvit | หญ้า | Злакові | Họ Hòa thảo | 禾本科