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Petals are modified
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaves
that surround the reproductive parts of
flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plan ...

flower
s. They are often brightly colored or unusually shaped to attract
pollinator A pollinator is an animal that moves pollen File:Pollen Tube.svg, Pollen Tube Diagram Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes ...

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 A sepal ( or ) is a part of the flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other p ...
s, that collectively form the ''calyx'' and lie just beneath the corolla. The calyx and the corolla together make up the
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (botany), calyx (sepals) and the corolla (flower), ...
, the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called
tepal A tepal is one of the outer parts of a flower A flower, sometimes known as a bloom or blossom, is the reproduction, reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). The biological ...
s. Examples of plants in which the term ''tepal'' is appropriate include
genera Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
such as ''
Aloe ''Aloe'' ( , ), also written ''Aloë'', is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and livin ...

Aloe
'' and ''
Tulipa Tulips (''Tulipa'') are a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification ...

Tulipa
''. Conversely, genera such as ''
Rosa Rosa or De Rosa may refer to: People *Rosa (given name) *Rosa (surname) Places *223 Rosa, an asteroid *Rosa, Alabama, United States *Rosa, Germany, in Thuringia, Germany *Rösa, a village and former municipality in Saxony-Anhalt, Germany *Rosà ...

Rosa
'' and ''
Phaseolus ''Phaseolus'' (bean, wild bean) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classi ...
'' have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in
petaloid monocots Lilioid monocots (lilioids, liliid monocots, petaloid monocots, petaloid lilioid monocots) is an informal name used for a grade Grade or grading may refer to: Arts and entertainment * Grade (band) Grade is a melodic hardcore band from Canada ...
, orders of monocots with brightly colored tepals. Since they include
Liliales Liliales is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and ...
, an alternative name is lilioid monocots. Although petals are usually the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the
grasses Poaceae () or Gramineae () is a large and nearly ubiquitous Family (biology), family of monocotyledonous flowering plants known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in ...
, either have very small petals or lack them entirely (apetalous).


Corolla

The role of the corolla in plant
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
has been studied extensively since
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all sp ...

Charles Darwin
postulated a theory of the origin of elongated corollae and corolla tubes. A corolla of separate petals, without fusion of individual segments, is ''
apopetalous Image:Mature flower diagram.svg, upright=1.4, Diagram showing the parts of a mature flower. In this example the perianth is separated into a calyx (sepals) and corolla (petals) Petals are modified Leaf, leaves that surround the reproductive parts ...
''. 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

Petals can differ dramatically in different species. The number of petals in a flower may hold clues to a plant's classification. For example, flowers on
eudicots The eudicots, Eudicotidae or eudicotyledons are a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage ...
(the largest group of dicots) most frequently have four or five petals while flowers on
monocots Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. The ...
have three or six petals, although there are many exceptions to this rule. The petal whorl or corolla may be either radially or bilaterally symmetrical (see
Symmetry in biology Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a plan ...
and
Floral symmetry Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
). If all of the petals are essentially identical in size and shape, the flower is said to be regular 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 Floral symmetry describes whether, and how, a flower A flower, sometimes known as a bloom or blossom, is the reproduction, reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). T ...
flowers may be seen in
orchid Orchidaceae ( ), commonly called the orchid family, is a diverse and widespread family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social ...

orchid
s and members of the . In many plants of the such as the sunflower, ''
Helianthus annuus ''Helianthus annuus'', the common sunflower, is a large annual plant, annual forb of the genus ''Helianthus'' grown as a crop for its edible oil and edible fruits. This sunflower species is also used as wild bird food, as livestock forage (as a me ...

Helianthus annuus
'', the circumference of the
flower head A pseudanthium (Greek for "false flower") is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower head, composite ...
is composed of ray florets. Each ray floret is anatomically an individual flower with a single large petal. Florets in the center of the disc typically have no or very reduced petals. In some plants such as ''
Narcissus Narcissus may refer to: Biology * Narcissus (plant), ''Narcissus'' (plant), a genus containing daffodils and others People * Narcissus (mythology), Greek mythological character * Narcissus (wrestler) (2nd century), assassin of the Roman emperor Co ...
'' the lower part of the petals or tepals are fused to form a floral cup (
hypanthium In angiosperms, a hypanthium or floral cup is a structure where basal portions of the calyx, the corolla, and the stamens form a cup-shaped tube. It is sometimes called a floral tube, a term that is also used for corolla tube and calyx tube. I ...
) above the ovary, and from which the petals proper extend. Petal often consists of two parts: the upper, broad part, similar to leaf blade, also called the ''blade'' and the lower part, narrow, similar to leaf
petiole Petiole may refer to: *Petiole (botany), the stalk of a leaf, attaching the blade to the stem *Petiole (insect anatomy), the narrow waist of some hymenopteran insects {{disambiguation ...
, called the ''claw'', separated from each other at the ''limb''. Claws are developed in petals of some flowers of the family ''
Brassicaceae Brassicaceae () or Cruciferae () is a medium-sized and economically important family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families ...
'', such as ''
Erysimum cheiri ''Erysimum cheiri'', syn. ''Cheiranthus cheiri'', the wallflower, is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A sp ...

Erysimum cheiri
''. The inception and further development of petals show a great variety of patterns. Petals of different species of plants vary greatly in color or color pattern, both in visible light and in ultraviolet. Such patterns often function as guides to pollinators and are variously known as
nectar guide Nectar guides are markings or patterns seen in flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit frui ...
s, pollen guides, and floral guides.


Genetics

The genetics behind the formation of petals, in accordance with the
ABC model of flower development The ABC model of flower development is a scientific model Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to understand, define, quantify, visualize, or simulate ...
, are that sepals, petals,
stamen The stamen (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ve ...
s, and
carpels '' stigmas and style Gynoecium (, from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided in ...
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.


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
hermaphroditic In reproductive biology, a hermaphrodite () is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life ...
flowers. Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the
stigma Stigma or plural stigmata, stigmas may refer to: * Social stigma, the disapproval of a person based on physical or behavioral characteristics that distinguish them from others Symbolism * Stigmata, bodily marks or wounds resembling the crucifix ...
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. 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).


Scent

The petals could produce different scents to allure desirable pollinators or repel undesirable pollinators. Some flowers will also mimic the scents produced by materials such as decaying meat, to attract pollinators to them.


Color

Various color 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 color of their petals as a signal to mutual pollinators to approach or keep away.Science Learning Hub. (2012). The University of Waikato. "Attracting pollinators". Date Retrieved: August 2013

/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. Collectively the scent, color, 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. 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


Wind pollination

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.


Attracting insects

Flowers have various regulatory mechanisms to attract insects. One such helpful mechanism is the use of color 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 color in a different way. The pohutukawa contains small petals also having bright large red clusters of stamens. 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 color-perception. Fragrancy can be especially useful for flowers that are pollinated at night by moths and other flying insects.


Attracting birds

Flowers are also pollinated by birds and must be large and colorful 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 color 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.


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 color but have the advantage of containing much nectar and a strong scent. These act as a useful mechanism in attracting the bat.Physics.org (2012). The University of Adelaide. "Flightless parrots, burrowing bats helped parasitic Hades flower". Date Retrieved August 2013

/ref>


References


Bibliography

* * {{Authority control
Plant morphology ''Plant morphology'' is the field in botany that studies the diversity in forms, with the naked eye or slight optical magnification. This is opposed to plant anatomy (see :Plant anatomy) that needs to cut into plants to be able to study its subject, ...
Plant reproductive system Pollination