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Flower Parts
Petals (Corolla)
The petals are the organs in the corolla whorl of floral appendages between
the sepals and stamens. They are usually showy and either pigmented or white.
Collectively, the petal and sepal whorls constitute the perianth.
Stamens
(Androecium)
Petals
(Corolla)
Perianth
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Pistil
(Gynoecium)
Sepals
(Calyx)
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Petals
There is a large variation in petal color, shape and size.
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Petals
Similar to the terminology for leaves,
the flat, expanded portion of the
petal is called the lamina.
The petal stalk (analogous to the
petiole) is referred to as the claw.
Claw
Claw
Petal
lamina
Nagoonberry (Rubus)
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Stork’s bill (Erodium)
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Petal
lamina
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Petals
Clawed petals can have a long,
basal stalk described as being
unguiculate.
Unguiculate
clawed petals
Unguiculate
clawed petals
Crape myrtle
Red orchid tree (Bauhinia)
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(Lagestroemia indica)
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Petals - Number
Dicot flowers often have petals in multiples of four or five.
Bluets
(Hedyotis)
Hawthorn (Crataegus)
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Petals - Number
Monocots usually have petals in multiples of three.
Petals
Sepals
Trillium (Trillium)
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Spiderwort (Tradescantia)
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Petals - Number
In most cases, petal number is consistent throughout the plant. However,
petal number may differ in the same inflorescence. In common rue, the initial
flower in the inflorescence has five petals, while all the others have four.
Four
petals
Four
petals
Five
petals
Four
petals
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Rue (Ruta graeveolens )
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Petals - Number
In Begonia, petal number varies depending on whether the flower is male or
female. The floral dimorphism occurs within the same inflorescence and may
serve to trick pollinators into visiting female flowers looking for a pollen reward.
Female and male
flowers
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Feale flower
Male flower
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Petals - Number
Chickweed flowers appear to have ten petals, but on close
inspection there are actually only five deeply divided (bifid) petals.
Bifid
petal
Chickweed (Stellaria)
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Petals - Number
When there is no clear morphological distinction between the sepals and
petals of the perianth, the petal-like structures are called tepals.
Tepals
Tepals
Carolina allspice (Calycanthus)
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Magnolia (Magnolia)
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Petals - Sympetaly
Petals may be fused (connate) and appear to be a single joined petal. Often, you
can identify the segments as in the petunia and moon flower that are five fused
petals. Technically, petal fusion is termed sympetaly.
5
1
4
2
3
Moonflower (Ipomoea)
Petunia (Petunia)
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Closed gentian (Gentian)
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Petals - Sympetaly
Through petal fusion, flowers can have extended floral tubes. Often, there are
nectaries inside the tube that entice bird or insect pollinators to enter the flower.
Kohleria
Cubanola
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Brugmansia
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Petals - Sympetaly
In most species, sympetaly occurs early in petal development in a process termed
congenital fusion. However, is some cases petal fusion occurs later in development
(postgenitally). This is called false sympetaly. In the examples below, it is most
evident in Lobelia tupa where the base of each petal is obviously separated.
In Correa, evidence of false
sympetally are the ridges that
run along the petal edges.
Correa
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Lobelia tupa
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Stackhousia
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Special petal modifications – Sympetaly (Window flowers)
In a window flower, the petal are fused at the tips and open near
the base. In Phyteuma (Campanulaceae), the expanding style
eventually pushes open through an opening created in the fused tip.
Fused
petal tips
Emerging stigmas
and styles
Phyteuma
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Petals
Through petal and sepal fusion and specialization there is a wonderful
diversity of flower forms.
Monodora
Thunbergia
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Crinodendron
Stanhopea
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Strongylodon
Dicentra
Physoplexis
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Orbea
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Petals
Many petal modifications are designed to interact with insect pollinators.
Petal marking on Phlox
to direct insects to
the sexual organs.
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The petals change color in
borage (Borago) to signal
insects when the flower is
ready for pollination.
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Foxglove (Delphinium)
flowers are adapted to bee
pollination with colored
guides on a landing platform
formed by the lower petal.
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Special petal modifications - Legumes
Some members of the legume family have butterfly-shaped (papilionaceous)
flowers. It shows how petals can have different shapes and functions in the same
flower. The flowers have petals modified into a large upper banner, two clawed side
wings, and two folded petals that form the lower keel that encloses the stamens.
Banner
Banner
Wing
Wing
Sepals
Wing
Wing
Yellowwood (Cladrastis)
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Keel
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Keel
Keel
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False indigo (Baptisia)
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Special petal modifications - Legumes
In a few papilionaceous species, the flowers are inverted in a process
called resupination where the banner is orientated below the wings
and keel. This occurs because the flower rotates on its floral axis.
Banner
Usual orientation
Inverted orientation
Wings and keel
Wings and keel
Banner
Centrosema virginianum
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Clitoria ternatum
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Special petal modifications - Spurs
Columbine (Aquilegia ) produces a flower with petals modified into a spur. The spur
is designed to entice pollinators to probe into the flower and facilitate pollination.
Sepal
Petal
spur
Petal
Petal
spur
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Petal
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Sepal
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Special petal modifications – Honey leaves
In Christmas rose (Helleborus), the sepals assume the showy role
usually performed by the petals. The petals are reduced and modified
into a basal ring of nectaries called nectar or honey leaves.
Stamens
Sepals
Stamens
Modified petals
with nectar glands
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Special petal modifications – Honey leaves
Similar petal-modified organs with nectar glands are
produced in black cumin (Nigella sativa).
Stamens
Sepals
Nectar
glands
Nectar
“leaves”
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Special petal modifications - Spurs
In bleeding hearts (Lamprocapnos spectabilis formerly Dicentra) flowers, the
outer two petals are pigmented and spurred. A pair of inner petals do not open
and form a covering over the anthers and stigma.
Outer petal
Outer petal
Stamens
Petal spur
Stamens
Pistil
Inner petals
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Special petal modifications - Operculum
In a few species, the sepals and petals will form a cap or lid that separates
and pops off to release the stamens. This structure is usually called an
operculum, but can also be referred to as a calyptra. Both operculum and
calyptra can also refer to several botanical structures that form a lid.
Operculum
Operculum
Gum tree (Eucalyptus)
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Schefflera pueckleri
(formerly Tupidanthus calyptratus)
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Special petal modifications – Corona
A corona (crown) is a group of petallike organs between the petals and
stamens. In oleander (Nerium), the
corona is a petal modification.
Corona
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Special petal modifications – Corona
In some members of the Caryophyllaceae, there is a petal outgrowth
where the claw joins the lamina called a coronal scale.
Corona
Coronal
scale
Coronal
scale
Fire pink
(Silene virginicus )
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Silene armeria
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Special petal modifications – Two-lipped
One specialized form of petal modification can be seen in two-lipped flowers .
Flowers typically have five petals where three petals form a lower lip and two form
the upper lip. Usually the sexual parts are arranged under the “hood” formed by
the upper lip and visiting insects are dusted with pollen on their backs.
4
5
2
3
1
Rosemarinus officinalis
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Salvia officinalis
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Prunella grandiflora
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Special petal modifications – Two-lipped
Two-lipped flowers are characteristic of the mint family (Lamiaceae) and for
this reason the flower form is termed labiate after the old family name
(Labiatae). Although two-lipped, division of the lower lip and reduction and
fusion of the upper lip can lead to a degree of diversity in appearance.
Ajuga reptans
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Salvia greggii
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Glechoma hederaceae
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Special petal modifications – Two-lipped
Some members of the Gesneriaceae have the typical three lower, two
upper lip labiate petal arrangement, but in Columnea two of the lower
lip petals appear with the two upper petals.
Primulina
Chirta
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Columnea
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Special petal modifications – Two-lipped
Most members of the snapdragon family (Scrophulariaceae) produce
labiate flowers in a three petal lower and two petal upper lip.
Mazus
Rehmannia
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Eremophila
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Calceolaria
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Special petal modifications – Two-lipped
In Lonicera, the upper lip is formed from four petals and the lower lip
having only a single petal.
Lonicera japonica
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Lonicera periclymenum
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Special petal modifications – Orchid labellum
In most orchids, there are three petal-like sepals, two lateral petals usually
similar in appearance to the sepals and a third petal modified into a lip (labellum).
Phaleonopsis
Sepal
Sepal
Petal
Petal
Sepal
Petal (Labellum – lip)
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Sepal
Petal
Petal
Sepal
Petal (Labellum – lip)
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Sepal
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Special petal modifications – Iris standards
The flower in Iris is highly modified. There are three sepals with a colored signal
pattern that acts as a landing area for bees. There are three upright petals. The
petal-like stigma and style has three segments that cover the stamens.
Petals
(Standards)
Stigma and
style
Stamen
Stigmatic lip
Style
arm
Style
Stamen
Sepals
(Falls)
The stigmatic surface
(lip) faces inward
toward the anthers.
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