Poaceae
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{{Taxobox
| color = lightgreen
| name = True grasses
| image = Meadow_Foxtail.jpg
| image_width = 240px
| image_caption = Flowering head of Meadow Foxtail
(Alopecurus pratensis),
with stamens exserted at anthesis
| regnum = Plantae
| divisio = Magnoliophyta
| classis = Liliopsida
| ordo = Poales
| familia = Poaceae
| familia_authority = (R.Br.) Barnhart
| subdivision_ranks = Subfamilies
| subdivision =
There are 7 subfamilies:
Subfamily Arundinoideae
Subfamily Bambusoideae
Subfamily Centothecoideae
Subfamily Chloridoideae
Subfamily Panicoideae
Subfamily Pooideae
Subfamily Stipoideae
}}
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 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 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.
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 grass phytoliths including ancestors of rice and bamboo in Cretaceous dinosaur coprolites ([1]), places the diversification of grasses to an earlier date. The growth of grasses from the base of the blade rather than from growing tips gave the grasses an edge under the pressures of grazing herbivores.
Cultivation and uses
Agricultural grasses grown 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 South and Southeast Asia, maize in Central and South America, and wheat and barley in the Americas and North Eurasia. Many other grasses are also grown for forage and fodder for animal food, particularly for sheep and cattle.
Some commonly known grass plants are:
See also
External links and references
- 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: descriptions, illustrations, identification, information retrieval.
- L. Watson and M. J. Dallwitz (1992 onwards). The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references.
Image:Harestail grass.jpgca:Gramínies cs:Lipnicovité da:Græs-familien de:Süßgräser es:Poácea eo:Poacoj fr:Poaceae it:Poaceae he:דגניים lt:Migliniai augalai hu:Pázsitfűfélék nl:Grassenfamilie ja:イネ科 no:Grasfamilien pl:Wiechlinowate pt:Poaceae th:หญ้า uk:Злакові vi:Họ Hòa thảo zh:禾本科
