Editing Poaceae (section)

== Description ==
{{plain image with caption|Grassy grass plant.svg|Diagram of a typical lawn grass plant|upright=1.35|caption position=top|triangle=triangle|triangle color=#43d050}}

Grasses may be [[annual plant|annual]] or [[perennial plant|perennial]] [[Herbaceous plant|herbs]],<ref name="Cope-2009"/>{{rp|10}} generally with the following characteristics (the image gallery can be used for reference): The [[Plant stem|stems]] of grasses, called [[Culm (botany)|culms]], are usually cylindrical (more rarely flattened, but not 3-angled) and are hollow, plugged at the [[node (botany)|nodes]], where the leaves are attached.<ref name="Cope-2009">{{cite book|first1=T.|last1=Cope|first2=A.|last2=Gray|title=Grasses of the British Isles|date=2009|publisher=[[Botanical Society of Britain and Ireland]]|location=London |isbn=9780901158420 }}</ref><ref name="Clayton-1986">{{cite book|first1=W.D.|last1=Clayton|first2=S.A.|last2=Renvoise|title=Genera Graminum: Grasses of the world|date=1986|publisher=Royal Botanic Garden, Kew|location=London|isbn=9781900347754 }}</ref> Grass [[Leaf|leaves]] are nearly always alternate and distichous (in one plane), and have parallel veins.<ref name="Cope-2009"/>{{rp|11}} Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins.<ref name="Cope-2009"/>{{rp|11}} The leaf blades of many grasses are hardened with [[silica]] [[phytolith]]s, which discourage grazing animals; some, such as [[Imperata cylindrica|sword grass]], are sharp enough to cut human skin. A membranous appendage or fringe of hairs called the [[ligule#Poaceae and Cyperaceae|ligule]] lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath.<ref name="Cope-2009"/>{{rp|11}}

[[File:Grassbluete numbers clones unlinked.svg|thumb|Inflorecence scheme and floral diagram. 1 – glume, 2 – lemma, 3 – awn, 4 – palea, 5 – lodicules, 6 – stamens, 7 – ovary, 8 – styles.]]

[[Flower]]s of Poaceae are characteristically arranged in [[spikelet]]s, each having one or more florets.<ref name="Cope-2009"/>{{rp|12}} The spikelets are further grouped into [[Raceme|panicles or spikes]]. The part of the spikelet that bears the florets is called the rachilla. A spikelet consists of two (or sometimes fewer) [[bracts]] at the base, called [[glumes]], followed by one or more florets.<ref name="Cope-2009"/>{{rp|13}} A floret consists of the flower surrounded by two bracts, one external—the [[lemma (botany)|lemma]]—and one internal—the [[palea (botany)|palea]]. The flowers are usually [[hermaphroditic]]—[[maize]] being an important exception—and mainly [[anemophily|anemophilous]] or wind-pollinated, although insects occasionally play a role.<ref>{{Cite journal | doi=10.1111/j.1440-6055.1964.tb00625.x|title = Insect Pollination of Grasses|journal = Australian Journal of Entomology| volume=3| pages=74|year = 1964|doi-access=| s2cid=264140616 }}</ref> The [[perianth]] is reduced to two scales, called ''[[lodicule]]s'',<ref name="Cope-2009"/>{{rp|11}} that expand and contract to spread the lemma and palea; these are generally interpreted to be modified sepals. The [[fruit]] of grasses is a [[caryopsis]], in which the seed coat is fused to the fruit wall.<ref name="Cope-2009"/>{{rp|16}}
A [[Tiller (botany)|tiller]] is a leafy shoot other than the first shoot produced from the seed.<ref name="Cope-2009"/>{{rp|11}}

=== Growth and development ===
[[File:Grassflowers.jpg|upright=1.15|thumb|Grass flowers]]
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 [[grazing|grazed]] or [[lawnmower|mown]] regularly without severe damage to the plant.<ref name="Attenborough-1984">{{cite book|title=The Living Planet|first=David |last=Attenborough|publisher=[[British Broadcasting Corporation]]|isbn=978-0-563-20207-3|year=1984|author-link=David Attenborough|title-link=The Living Planet }}</ref>{{rp|113–114}}

Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), [[stolon]]iferous, and [[rhizome|rhizomatous]].<ref>{{Cite book|last=Staller|first=John|url=https://books.google.com/books?id=jHL1dry3W_oC&pg=PA131|title=Maize Cobs and Cultures: History of Zea mays L.|date=2009-12-02|publisher=Springer Science & Business Media|isbn=978-3-642-04506-6|language=en}}</ref>
The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. There are both [[C3 carbon fixation|C3]] and [[C4 carbon fixation|C4]] grasses, referring to the photosynthetic pathway for carbon fixation. The C4 grasses have a photosynthetic pathway, linked to specialized [[Kranz anatomy|Kranz leaf anatomy]], which allows for increased [[water use efficiency]], rendering them better adapted to hot, arid environments.<ref>{{Cite book|last=Gibson|first=David J.|url=https://books.google.com/books?id=QZIUDAAAQBAJ|title=Grasses and Grassland Ecology|date=2009|publisher=Oxford University Press|isbn=978-0-19-852918-7|language=en|page=63}}</ref>

The C3 grasses are referred to as "cool-season" grasses, while the C4 plants are considered "warm-season" grasses.<ref name="Cope-2009"/>{{rp|18–19}}
* 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]].

Although the C4 species are all in the [[PACMAD clade]] (see diagram below), it seems that various forms of C4 have arisen some twenty or more times, in various subfamilies or genera. In the ''[[Aristida]]'' genus for example, one species (''A. longifolia'') is C3 but the approximately 300 other species are C4. As another example, the whole tribe of [[Andropogoneae]], which includes [[maize]], [[sorghum]], [[sugar cane]], "[[Job's tears]]", and [[bluestem grass]]es, is C4.<ref name="GPWGII-2012"/> Around 46 percent of grass species are C4 plants.<ref>{{Cite book|last=Harris|first=Stephen A.|url=https://books.google.com/books?id=QkedAwAAQBAJ&pg=PT28|title=Grasses|date=2014-04-15|publisher=Reaktion Books|isbn=978-1-78023-313-0|language=en}}</ref>