Petal

corollapetalscorollasapetalousclawsclawcorolla tubecorollaepetaloidperianth
Petals are modified leaves that surround the reproductive parts of flowers.wikipedia
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Flower

flowersfloralflowering
Petals are modified leaves that surround the reproductive parts of flowers.

Sepal

calyxsepalscalyces
Petals are usually accompanied by another set of special leaves called sepals, that collectively form the calyx and lie just beneath the corolla.
Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom.

Perianth

perianth tubecoronaperigone
The calyx and the corolla together make up the perianth.
The perianth (perigonium, perigon or perigone) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals).

Tepal

tepalsperigoneperianth
When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals.
The term is used when these parts cannot easily be classified as either sepals or petals.

Lilioid monocots

lilioid monocotpetaloid monocotsPetaloidea
When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly coloured tepals.
Petaloid monocots refers to the flowers having tepals which all resemble petals (petaloid).

Tulip

tulipsTulipatulip bulb
Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa.
The two whorls represent three petals and three sepals, but are termed tepals because they are nearly identical.

Pollinator

pollinatorspollinatingpollinated
They are often brightly colored or unusually shaped to attract pollinators.
Many bee flies, and some Tabanidae and Nemestrinidae are particularly adapted to pollinating fynbos and Karoo plants with narrow, deep corolla tubes, such as Lapeirousia species.

Leaf

leavesaxilfoliage
Petals are modified leaves that surround the reproductive parts of flowers.

Rose

Rosarosesred rose
Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals.
Most are double-flowered with many or all of the stamens having mutated into additional petals.

Merosity

4-merouspentamerousmerous
The number of petals in a flower may hold clues to a plant's classification.
It is most commonly used in the context of flowers where it refers to the number of sepals in a whorl of the calyx, the number of petals in a whorl of the corolla, the number of stamens in a whorl of the androecium, or the number of carpels in a whorl of the gynoecium.

Orchidaceae

orchidorchidsorchid family
Examples of zygomorphic flowers may be seen in orchids and members of the pea family.
Among these are: bilateral symmetry of the flower (zygomorphism), many resupinate flowers, a nearly always highly modified petal (labellum), fused stamens and carpels, and extremely small seeds.

Symmetry in biology

bilateral symmetryradial symmetrybilaterally symmetrical
The petal whorl or corolla may be either radially or bilaterally symmetrical (see Symmetry in biology and Floral symmetry).
Roughly identical flower parts – petals, sepals, and stamens – occur at regular intervals around the axis of the flower, which is often the female part, with the carpel, style and stigma.

Narcissus (plant)

Narcissusdaffodildaffodils
In some plants such as 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.
Closest to the stem (proximal) is a floral tube above the ovary, then an outer ring composed of six tepals (undifferentiated sepals and petals), and a central disc to conical shaped corona.

Monocotyledon

Monocotsmonocotmonocotyledonous
For example, flowers on eudicots (the largest group of dicots) most frequently have four or five petals while flowers on monocots have three or six petals, although there are many exceptions to this rule.
In nearly all cases the perigone consists of two alternating trimerous whorls of tepals, being homochlamydeous, without differentiation between calyx and corolla.

Fabaceae

Leguminosaelegume familylegume
Examples of zygomorphic flowers may be seen in orchids and members of the pea family.
The flowers often have five generally fused sepals and five free petals.

Hypanthium

floral cupflower cupfloral tube
In some plants such as 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.
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.

Pseudanthium

flower headsflower headcapitula
In many plants of the aster family such as the sunflower, Helianthus annuus, the circumference of the flower head is composed of ray florets.
The disk flowers in the center of the pseudanthium are actinomorphic and the corolla is fused into a tube.

Asteraceae

daisy familysunflower familydisc floret
In many plants of the aster family such as the sunflower, Helianthus annuus, the circumference of the flower head is composed of ray florets.
The corolla of the ray flower may have 2 tiny teeth opposite the 3-lobed strap, or tongue, indicating evolution by fusion from an originally 5-part corolla.

Brassicaceae

mustard familyCruciferaecrucifers
Claws are developed in petals of some flowers of the family Brassicaceae, such as Erysimum cheiri.
The alternative older name, Cruciferae, meaning "cross-bearing", describes the four petals of mustard flowers, which resemble a cross.

ABC model of flower development

foliar theoryThe ABC Model of Flower DevelopmentABC model
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.
These verticils follow an acropetal development, giving rise to sepals, petals, stamens and carpels.

Floral symmetry

zygomorphicactinomorphicstar-symmetrical
Examples of zygomorphic flowers may be seen in orchids and members of the pea family. The petal whorl or corolla may be either radially or bilaterally symmetrical (see Symmetry in biology and Floral symmetry).
Monocots are identifiable by their trimerous petals, thus monocots often have rotational symmetry of order 3.

Plant reproductive morphology

monoeciousdioeciousbisexual
Pollen is produced by the male flower or by the male organs of hermaphroditic flowers.
A "complete" flower, like that of Ranunculus glaberrimus shown in the figure, has a calyx of outer sepals and a corolla of inner petals.

Stamen

antheranthersstamens
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.

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They are often brightly colored or unusually shaped to attract pollinators.

Genus

generageneric namegeneric
Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa.