Petal

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Petal

A petal (from Ancient Greek

Ancient Greek

Ancient Greek is the historical stage in the development of the Greek language spanning across the Archaic Greece , Classical Greece , and Hellenistic civilization periods of ancient Greece and the classical antiquity....
petalon "leaf", "thin plate") is one member or part of the corolla of a flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproduction structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds....
. The corolla is the name for all of the petals of a flower; the inner perianth whorl

Whorl

Whorl is a type of spiral pattern.Other meanings of whorl include:* Whorl , a single, complete 360? turn in the spiral growth of a mollusc shell...
, term used when this is not the same in appearance (color, shape) as the outermost whorl (the calyx) and is used to attract pollinator

Pollinator

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A petal (from Ancient Greek

Ancient Greek

Flower

Whorl

Pollinator

A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female carpel of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain....
s based on its bright color. It is the inner part of the perianth that comprises the sterile parts of a flower and consists of inner and outer tepal
Tepal

Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term tepal is usually used when all segments of the perianth are of similar shape and color, or undifferentiated....
s. These tepals are usually differentiated into petals and sepal

Sepal

A sepal is a part of the flower of angiosperms . Sepals in a "typical" flower are green and lie under the more conspicuous petals. As a collective unit the sepals are called the Wiktionary:calyx, and the collection of petals is called the Wiktionary:corolla....
s. The term "tepal" is usually applied when the petals and sepals are similar in shape and color. In a "typical" flower the petals are showy and colored and surround the reproductive parts. The number of petals in a flower (see merosity
Tepal

Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term tepal is usually used when all segments of the perianth are of similar shape and color, or undifferentiated....
) is indicative of the plant's classification: eudicots

Eudicots

Eudicots and Eudicotyledons are terms introduced by Doyle & Hotton to refer to a group of flowering plants that had been called "tricolpates" or "non-Magnoliid dicots" by previous authors....
(the largest group of dicots

Dicotyledon

Dicotyledons, or "dicots", is a name for a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group....
) having typically four or five petals and monocots

Monocotyledon

Monocotyledons or monocots are one of two major groups of flowering plants that are traditionally recognised, the other being dicotyledons or dicots....
and magnoliids having three, or some multiple of three, petals.

The genetics behind the formation of petals, in accordance with the ABC model of flower development, are that sepals, petals, stamens, and carpels are modified versions of each other. It seems that the mechanisms to form petals evolved a small number of times (perhaps only once), rather than evolving independently from stamens in a large number of plants.

There exists considerable variation in form of petals among the flowering plant

Flowering plant

The flowering plants or angiosperms are the most widespread group of Embryophytes. The flowering plants and the gymnosperms are the only extant groups of Spermatophyte....
s. The petals can be united towards the base, forming a floral tube. In some flowers, the entire perianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals, petals, and stamens attached to the rim of the cup.

The flowers of some species lack or have very much reduced petals. These are often referred to as apetalous. Examples of flowers with much reduced perianths are found among the grasses

Poaceae

Poaceae or Gramineae is a family in the Class Liliopsida of the Magnoliophyta. Plants of this family are usually called grasses; the shrub- or tree-like plants in this family are called bamboo ....
.

The petals are usually the most conspicuous parts of a flower, and the petal whorl or corolla may be either radially or bilaterally symmetrical. 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 flowers may be seen in orchids and members of the pea family

Fabaceae

Fabaceae or Leguminosae is a large and economically important family of flowering plants, which is commonly known as the legume family, pea family, bean family or pulse family....
. The petal is the colorful, often showy part of a plant.

Other structures which may look like petals

Some plants have petaloid stamens, in plants like Canna
Canna (plant)

Canna is a genus of approximately twenty species of flowering plants. The closest living relations to cannas are the other plant families of the order Zingiberales, that is the gingers, bananas, Marantaceae, heliconias, strelitzias, etc....
that have true petals and staminode

Staminode

In botany, a staminode is an often rudimentary, sterile or abortive stamen. This means that it does not produce pollen. Staminodes are frequently inconspicuous and stamen-like, usually occurring at the inner whorl of the flower, but are also sometimes long enough to protrude from the corolla....
s, the stamen (staminodes) are modified to look like large showy petals.

A number of plants have bract

Bract

In botany, a bract is a modified or specialized leaf. Bracts are ordinarily associated with reproductive structures . They are ordinarily reduced in size relative to foliage leaves, or of a different color or texture from foliage leaves, or both....
s that resemble petals for example in Bougainvillea
Bougainvillea

Bougainvillea is a genus of flowering plants native to South America from Brazil west to Peru and south to southern Argentina . Different authors accept between four and 18 species in the genus....
and Cornus florida (flowering dogwood). Petal-like bracts are common features in some plant families like Euphorbiaceae

Euphorbiaceae

The Spurge family is a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees....
.

In many plants of the aster family

Asteraceae

The family Asteraceae or Compositae is the largest family of flowering plants, in terms of number of species.The name 'Asteraceae' is derived from the type genus Aster , while 'Compositae', an older but still valid name, means composite and refers to the characteristic inflorescence, a special type of pseudanthium found in o...
such as the sunflower, Helianthus annuus, the circumference of the flower head

Head (botany)

The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae shows lesser degrees of specialization....
is composed of ray florets. Each ray floret is anatomically an individual flower with a single large petal.

Corolla

Corolla is the collective term for petal

Petal

A petal is one member or part of the Corolla of a flower. The corolla is the name for all of the petals of a flower; the inner perianth whorl, term used when this is not the same in appearance as the outermost whorl and is used to attract pollinators based on its advertising coloration....
s of a flower taken as a group within the calyx. Normally the corolla is the most conspicuous part of a flower and of a bright colour other than green. The concept of corolla description is widely used in botany

Botany

Botany, plant science, phytology, or plant biology is a branch of biology and is the Scientific method of plant life and development....
as a primary determinant of vascular plant

Vascular plant

Vascular plants are those plants that have lignin tissue for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms....
identification. Alternatively the corolla may be considered as the inner whorl

Whorl

Whorl is a type of spiral pattern.Other meanings of whorl include:* Whorl , a single, complete 360? turn in the spiral growth of a mollusc shell...
of the perianth structure. The role of the corolla in plant evolution

Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
has been studied extensively since Darwin

Charles Darwin

Charles Robert Darwin Royal Society was an English people natural history who realised and presented compelling evidence that all species of life have evolution over time from common descent, through the process he called natural selection....
postulated a theory of the origin of elongated corollae.