View source for Petal

{{Short description|Part of most types of flower}}
{{Other uses}}
[[Image:Mature flower diagram.svg|thumb|upright=1.4|In a mature flower, the [[perianth]] consists of a calyx&nbsp;([[sepal]]s) and the corolla&nbsp;(petals) it supports.]]
'''Petals''' are modified [[leaves]] that surround the reproductive parts of [[flower]]s. They are often [[advertising coloration|brightly coloured]] or unusually shaped to attract [[pollinator]]s. All of the petals of a flower are collectively known as the '''''corolla'''''. Petals are usually accompanied by another set of modified leaves called [[sepal]]s, that collectively form the ''calyx'' and lie just beneath the corolla. The calyx and the corolla together make up the [[perianth]], the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called [[tepal]]s. Examples of plants in which the term ''tepal'' is appropriate include [[Genus|genera]] such as ''[[Aloe]]'' and ''[[Tulipa]]''. Conversely, genera such as ''[[Rose|Rosa]]'' and ''[[Phaseolus]]'' have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in [[petaloid monocots]], orders of monocots with brightly coloured tepals. Since they include [[Liliales]], an alternative name is lilioid monocots.
Although petals are usually the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the [[Poaceae|grasses]], either have very small petals or lack them entirely (apetalous).
{{Multiple image
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| image1 = Petal-sepal.jpg
| caption1 = [[Tetramery (botany)|Tetrameric]] flower of a primrose [[Onagraceae|willowherb]] (''[[Ludwigia octovalvis]]'') showing petals and sepals
| image2 = Tulip Tulipa clusiana 'Lady Jane' Rock Ledge Flower 2000px.jpg
| caption2 = A [[tulip]]'s actinomorphic flower with three of both petals and sepals, similar enough to be considered [[tepal]]s
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==Corolla==
[[File:Perianth morphology fusion aposepalous apopetalous.png|thumb|Apopetalous corolla|alt=Diagram of apopetalous corolla]]
[[File:2007 brugmansia aurea.jpg|thumb|Tubular-campanulate corolla, bearing long points and emergent from tubular calyx (''[[Brugmansia aurea]]'', Golden Angel's Trumpet, family [[Solanaceae]]).]]
The collection of all petals in a flower is referred to as the corolla. The role of the corolla in plant [[evolution]] has been studied extensively since [[Charles Darwin]] postulated a theory of the origin of elongated corollae and corolla tubes.<ref>{{cite journal|author=L. Anders Nilsson| title=The evolution of flowers with deep corolla tubes |journal=Nature |volume=334 |issue=6178 |pages=147–149 |year=1988 |doi=10.1038/334147a0 |bibcode=1988Natur.334..147N| s2cid=4342356 }}</ref>
A corolla of separate petals, without fusion of individual segments, is ''[[wikt:apopetalous|apopetalous]]''. If the petals are free from one another in the corolla, the plant is ''polypetalous'' or ''choripetalous''; while if the petals are at least partially fused, it is ''gamopetalous'' or ''sympetalous''. In the case of fused tepals, the term is ''syntepalous''. The corolla in some plants forms a tube.
== Variations ==
[[File:Pelargonium peltatum 9245s.jpg|thumb|''[[Pelargonium peltatum]]'' flowers resemble those of [[geranium]]s, but are conspicuously [[zygomorphic]].]]
[[File:Geranium incanum 9156s.jpg|thumb|''Geranium incanum'', with an actinomorphic flower typical of the genus]] [[File:White pea flower.jpg|thumb|The white flower of ''[[Pisum sativum]]'', the Garden Pea: an example of a zygomorphic flower.]]
[[File:20140226Narcissus2.jpg|thumb|''[[Narcissus pseudonarcissus]]'' showing (from bend to tip of flower) [[spathe]], [[floral cup]], tepals, and [[perianth#corona|corona]]]]
[[File:使君子Combretum indicum 20210523080843 01.jpg|thumb|The petals of ''[[Combretum indicum]]'' grow on the sepals of the flower.]]
Petals can differ dramatically in different species.  The [[merosity|number of petals in a flower]] may hold clues to a plant's classification.  For example, flowers on [[eudicots]] (the largest group of [[dicots]]) most frequently have four or five petals while flowers on [[monocotyledon|monocots]] have three or six petals, although there are many exceptions to this rule.<ref>{{cite journal |title= The origin and diversification of angiosperms |author= Soltis, Pamela S.|author-link = Pamela S. Soltis|author2 = Douglas E. Soltis |journal= American Journal of Botany |year= 2004 |volume= 91 | pages= 1614–1626 | doi= 10.3732/ajb.91.10.1614 |issue=10 |pmid=21652312|doi-access= free }}</ref>
The petal whorl or corolla may be either radially or bilaterally [[Floral symmetry|symmetrical]]. If all of the petals are essentially identical in size and shape, the flower is said to be '''regular'''<ref name=EB1911/> or '''actinomorphic''' (meaning "ray-formed"). Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed '''irregular''' or '''zygomorphic''' (meaning "yoke-" or "pair-formed"). In ''irregular'' flowers, other floral parts may be modified from the ''regular'' form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in [[orchid]]s and members of the [[pea family]].
In many plants of the [[aster family]] such as the sunflower, ''[[Helianthus annuus]]'', the circumference of the [[flower head]] is composed of [[ray floret]]s.  Each ray floret is anatomically an individual flower with a single large petal.  Florets in the centre of the disc typically have no or very reduced petals. In some plants such as ''[[Narcissus (plant)|Narcissus]]'', the lower part of the petals or tepals are fused to form a floral cup ('''[[hypanthium]]''') above the ovary, and from which the petals proper extend.{{sfn|Simpson|2011|loc=p. 365}}{{sfn|Foster|2014|loc=[http://plant-phytography.blogspot.ca/2012/10/hypanthium-cup-shaped-or-tubular.html Hypanthium]}}<ref name=Graham/>
A petal often consists of two parts: the upper broader part, similar to a leaf blade, also called the ''blade;'' and the lower narrower part, similar to a leaf [[Petiole (botany)|petiole]], called the ''claw'',<ref name=EB1911>{{Cite EB1911|wstitle=Flower|first=Alfred Barton|last=Rendle|volume=10|pages=561–563}}</ref> separated from each other at the ''limb''. Claws are distinctly developed in petals of some flowers of the family ''[[Brassicaceae]]'', such as ''[[Erysimum cheiri]]''.
The inception and further development of petals show a great variety of patterns.<ref>Sattler, R. 1973. ''Organogenesis of Flowers. A Photographic Text-Atlas''. University of Toronto Press.</ref> Petals of different species of plants vary greatly in colour or colour pattern, both in visible light and in ultraviolet. Such patterns often function as guides to pollinators and are variously known as [[nectar guide]]s, pollen guides, and floral guides.
==Genetics==
The genetics behind the formation of petals, in accordance with the [[ABC Model of Flower Development|ABC model of flower development]], are that sepals, petals, [[stamen]]s, and [[carpels]] are modified versions of each other.  It appears that the mechanisms to form petals evolved very few times (perhaps only once), rather than evolving repeatedly from stamens.<ref>{{cite journal |doi= 10.3732/ajb.0800038 |title= One size fits all? Molecular evidence for a commonly inherited petal identity program in Ranunculales |year= 2008 |author= Rasmussen, D. A. |journal= American Journal of Botany |last2= Kramer |first2= E. M. |last3= Zimmer |first3= E. A. |volume= 96 |pages= 96–109 |pmid= 21628178 |issue= 1 |url= https://dash.harvard.edu/bitstream/handle/1/8519266/Rasmussen%20et%20al.pdf?sequence=2 |doi-access= free }}</ref>
==Significance of pollination==
Pollination is an important step in the sexual reproduction of higher plants.  Pollen is produced by the male flower or by the male organs of [[monoecious|hermaphroditic]] flowers.
Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the [[stigma (botany)|stigma]] of the same or nearby flowers. However, pollinators are rather selective in determining the flowers they choose to pollinate. This develops competition between flowers and as a result flowers must provide incentives to appeal to pollinators (unless the flower self-pollinates or is involved in wind pollination). Petals play a major role in competing to attract pollinators. Henceforth pollination dispersal could occur and the survival of many species of flowers could prolong.
==Functions and purposes==
Petals have various functions and purposes depending on the type of plant. In general, petals operate to protect some parts of the flower and attract/repel specific pollinators.
===Function===
This is where the positioning of the flower petals are located on the flower is the corolla e.g. the buttercup having shiny yellow flower petals which contain guidelines amongst the petals in aiding the pollinator towards the nectar. Pollinators have the ability to determine specific flowers they wish to pollinate.<ref>Cares-Suarez, R,  Poch, T, Acevedo, R.F, Acosta-Bravo, I, Pimentel, C,  Espinoza, C, Cares, R.A, Munoz, P, Gonzalez, A.V, Botto-Mahan, C (2011) Do pollinators respond in a dose-dependent manner to flower herbivory?: An experimental assessment in Loasa tricolor (Loasaceae). [[Gayana. Botánica]], Volume 68, Pages 176–181</ref> Using incentives, flowers draw pollinators and set up a mutual relation between each other in which case the pollinators will remember to always guard and pollinate these flowers (unless incentives are not consistently met and competition prevails).<ref>{{cite journal |author1=Chamberlain S.A |author2=Rudgers J.A | year = 2012 | title = How do plants balance multiple mutualists? Correlations among traits for attracting protective bodyguards and pollinators in cotton (Gossypium) | journal = Evolutionary Ecology | volume = 26 | pages = 65–77 | doi=10.1007/s10682-011-9497-3|s2cid=13996011 }}</ref>
===Scent===
The petals could produce different scents to allure desirable pollinators<ref>{{Cite journal|last1=Toh|first1=Conie|last2=Mohd-Hairul|first2=Ab. Rahim|last3=Ain|first3=Nooraini Mohd.|last4=Namasivayam|first4=Parameswari|last5=Go|first5=Rusea|last6=Abdullah|first6=Nur Ashikin Psyquay|last7=Abdullah|first7=Meilina Ong|last8=Abdullah|first8=Janna Ong|date=2017-11-02|title=Floral micromorphology and transcriptome analyses of a fragrant Vandaceous Orchid, Vanda Mimi Palmer, for its fragrance production sites|journal=BMC Research Notes|volume=10|issue=1|pages=554|doi=10.1186/s13104-017-2872-6|pmid=29096695|pmc=5669028|issn=1756-0500 |doi-access=free }}</ref> or repel undesirable pollinators.<ref>{{Cite journal|last1=Kessler|first1=Danny|last2=Kallenbach|first2=Mario|last3=Diezel|first3=Celia|last4=Rothe|first4=Eva|last5=Murdock|first5=Mark|last6=Baldwin|first6=Ian T|date=2015-07-01|title=Abstract|journal=eLife|language=en|volume=4|doi=10.7554/elife.07641.001|issn=2050-084X|doi-access=free}}</ref> Some flowers will also mimic the scents produced by materials such as decaying meat, to attract pollinators to them.<ref>{{cite journal|author=More, M, Cocucci, A.A, Raguso, R.A|year=2013|title=The importance of oligosulfides in the attraction of fly pollinators to the brood-site deceptive species ''Jaborosa rotacea'' (Solanaceae)|journal=International Journal of Plant Sciences|volume=174|issue=6|pages=863–876|doi=10.1086/670367|jstor=10.1086/670367|hdl=11336/1416|s2cid=3260154|url=http://ri.conicet.gov.ar/bitstream/11336/1416/1/Mor__al_2013proof.pdf|hdl-access=free}}</ref>
===Colour===
Various colour traits are used by different petals that could attract pollinators that have poor smelling abilities, or that only come out at certain parts of the day. Some flowers can change the colour of their petals as a signal to mutual pollinators to approach or keep away.<ref name="SLH">Science Learning Hub. (2012). The University of Waikato. "Attracting pollinators". Date Retrieved: August 2013. [http://www.sciencelearn.org.nz/Contexts/Pollination/Science-Ideas-and-Concepts/Attracting-pollinators] {{Webarchive|url=https://web.archive.org/web/20161203173510/http://sciencelearn.org.nz/Contexts/Pollination/Science-Ideas-and-Concepts/Attracting-pollinators|date=2016-12-03}}</ref>
===Shape and size===
Furthermore, the shape and size of the flower/petals are important in selecting the type of pollinators they need. For example, large petals and flowers will attract pollinators at a large distance or that are large themselves.<ref name=SLH/>
Collectively, the scent, colour, and shape of petals all play a role in attracting/repelling specific pollinators and providing suitable conditions for pollinating. Some pollinators include insects, birds, bats, and wind.<ref name=SLH/>
In some petals, a distinction can be made between a lower narrowed, stalk-like basal part referred to as the claw, and a wider distal part referred to as the blade (or limb). Often, the claw and blade are at an angle with one another.
==Types of pollination==
{{Main|Pollination syndrome}}
===Wind pollination===
{{main|Anemophily}}
Wind-pollinated flowers often have small, dull petals and produce little or no scent. Some of these flowers will often have no petals at all. Flowers that depend on wind pollination will produce large amounts of pollen because most of the pollen scattered by the wind tends to not reach other flowers.<ref>{{cite journal|title=Wind Pollination in the Angiosperms: Evolutionary and Environmental Considerations|author=Donald R. Whitehead|journal=Evolution|volume=23|issue=1|year=1969|pages=28–35|doi=10.2307/2406479|pmid = 28562955|jstor=2406479}}</ref>
===Attracting insects===
Flowers have various regulatory mechanisms to attract insects. One such helpful mechanism is the use of colour guiding marks. Insects such as the bee or butterfly can see the ultraviolet marks which are contained on these flowers, acting as an attractive mechanism which is not visible towards the human eye. Many flowers contain a variety of shapes acting to aid with the landing of the visiting insect and also influence the insect to brush against anthers and stigmas (parts of the flower). One such example of a flower is the pohutukawa (''Metrosideros excelsa''), which acts to regulate colour in a different way. The pohutukawa contains small petals also having bright large red clusters of stamens.<ref name=SLH/>
Another attractive mechanism for flowers is the use of scents which are highly attractive to humans. One such example is the rose. On the other hand, some flowers produce the smell of rotting meat and are attractive to insects such as flies. Darkness is another factor that flowers have adapted to as nighttime conditions limit vision and colour-perception. Fragrancy can be especially useful for flowers that are pollinated at night by moths and other flying insects.<ref name=SLH/>
===Attracting birds===
Flowers are also pollinated by birds and must be large and colourful to be visible against natural scenery. In New Zealand, such bird–pollinated native plants include: kowhai (''Sophora'' species), flax (''Phormium tenax'') and kaka beak (''Clianthus puniceus''). Flowers adapt the mechanism on their petals to change colour in acting as a communicative mechanism for the bird to visit. An example is the tree fuchsia (''Fuchsia excorticata''), which are green when needing to be pollinated and turn red for the birds to stop coming and pollinating the flower.<ref name=SLH/>
===Bat-pollinated flowers===
Flowers can be pollinated by short-tailed bats. An example of this is the dactylanthus (''Dactylanthus taylorii''). This plant has its home under the ground acting the role of a parasite on the roots of forest trees. The dactylanthus has only its flowers pointing to the surface and the flowers lack colour but have the advantage of containing much nectar and a strong scent. These act as a useful mechanism in attracting the bat.<ref>Physics.org (2012). The University of Adelaide. "Flightless parrots, burrowing bats helped parasitic Hades flower". Date Retrieved August 2013. [http://phys.org/news/2012-10-flightless-parrots-burrowing-parasitic-hades.html]</ref>
== References ==
{{Reflist|30em|refs=
<ref name=Graham>{{cite journal|last1=Graham|first1=S. W.|last2=Barrett|first2=S. C. H.|title=Phylogenetic reconstruction of the evolution of stylar polymorphisms in ''Narcissus'' (Amaryllidaceae)|journal=American Journal of Botany|date=1 July 2004|volume=91|issue=7|pages=1007–1021|doi=10.3732/ajb.91.7.1007|pmid=21653457|doi-access=free}}</ref>}}
== Bibliography==
* {{cite book|last=Simpson|first=Michael G.|title=Plant Systematics|year=2011|publisher=Academic Press|isbn=978-0-08-051404-8|url=https://books.google.com/books?id=Ia2eIPVksMMC}}
*{{cite web|last1=Foster|first1=Tony|title=Botany Word of the Day|url=http://plant-phytography.blogspot.com/|website=Phytography|access-date=27 November 2014|ref={{harvid|Foster|2014}}}}
{{Commons category|Petals}}
{{Botany}}
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[[Category:Plant morphology]]
[[Category:Plant reproductive system]]
[[Category:Pollination]]