Petal

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Diagram showing the parts of a mature flower. In this example, the perianth is separated into a calyx (sepals) and corolla (petals) Mature flower diagram.svg
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 leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the corolla. Petals are usually accompanied by another set of modified leaves called sepals, 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 tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa . Conversely, genera such as 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 colored tepals. Since they include Liliales, an alternative name is lilioid monocots.

Contents

Although petals are usually the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the grasses, either have very small petals or lack them entirely (apetalous).

Petal-sepal.jpg
Tetrameric flower of a primrose willowherb ( Ludwigia octovalvis ) showing petals and sepals
Tulip Tulipa clusiana 'Lady Jane' Rock Ledge Flower 2000px.jpg
A tulip's actinomorphic flower with three petals and three sepals, that collectively present a good example of an undifferentiated perianth. In this case, the word "tepals" is used.

Corolla

Apopetalous corolla Perianth morphology fusion aposepalous apopetalous.png
Apopetalous corolla
Tubular-campanulate corolla, bearing long points and emergent from tubular calyx (Brugmansia aurea, Golden Angel's Trumpet, family Solanaceae). 2007 brugmansia aurea.jpg
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. [1]

A corolla of separate petals, without fusion of individual segments, is 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

Pelargonium peltatum, the Ivy-leaved Pelargonium : its floral structure is almost identical to that of geraniums, but it is conspicuously zygomorphic Pelargonium peltatum 9245s.jpg
Pelargonium peltatum , the Ivy-leaved Pelargonium : its floral structure is almost identical to that of geraniums, but it is conspicuously zygomorphic
Geranium incanum, with an actinomorphic flower typical of the genus Geranium incanum 9156s.jpg
Geranium incanum, with an actinomorphic flower typical of the genus
The white flower of Pisum sativum, the Garden Pea: an example of a zygomorphic flower. White pea flower.jpg
The white flower of Pisum sativum , the Garden Pea: an example of a zygomorphic flower.
Narcissus pseudonarcissus, the Wild Daffodil, showing ( from bend to tip of flower ) spathe, floral cup, tepals, corona 20140226Narcissus2.jpg
Narcissus pseudonarcissus , the Wild Daffodil, showing ( from bend to tip of flower ) spathe, floral cup, tepals, corona
The petals of Combretum indicum grow on the sepals of the flower. Shi Jun Zi Combretum indicum 20210523080843 01.jpg
The petals of Combretum indicum grow on the sepals of the flower.

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 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. [2]

The petal whorl or corolla may be either radially or bilaterally symmetrical (see Symmetry in biology and Floral symmetry). If all of the petals are essentially identical in size and shape, the flower is said to be regular [3] 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.

In many plants of the aster family such as the sunflower, Helianthus annuus , the circumference of the flower head 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 , 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. [4] [5] [6]

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, called the claw, [3] 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. [7] 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 guides, pollen guides, and floral guides.

Genetics

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 appears that the mechanisms to form petals evolved very few times (perhaps only once), rather than evolving repeatedly from stamens. [8]

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 flowers.

Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the 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. [9] 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). [10]

Scent

The petals could produce different scents to allure desirable pollinators [11] or repel undesirable pollinators. [12] Some flowers will also mimic the scents produced by materials such as decaying meat, to attract pollinators to them. [13]

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. [14]

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. [14] 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. [14] 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. [15]

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. [14] 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. [14]

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. [14]

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. [16]

Related Research Articles

<span class="mw-page-title-main">Sepal</span> Any of the separate parts of the calyx of a flower (excluding the bracts), usually green

A sepal is a part of the flower of angiosperms. Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom.

<span class="mw-page-title-main">Pseudocopulation</span> Biological process

Pseudocopulation describes behaviors similar to copulation that serve a reproductive function for one or both participants but do not involve actual sexual union between the individuals. It is most generally applied to a pollinator attempting to copulate with a flower. Some flowers mimic a potential female mate visually, but the key stimuli are often chemical and tactile. This form of mimicry in plants is called Pouyannian mimicry.

<span class="mw-page-title-main">Tepal</span> One of the outer parts of a flower

A tepal is one of the outer parts of a flower. The term is used when these parts cannot easily be classified as either sepals or petals. This may be because the parts of the perianth are undifferentiated, as in Magnolia, or because, although it is possible to distinguish an outer whorl of sepals from an inner whorl of petals, the sepals and petals have similar appearance to one another. The term was first proposed by Augustin Pyramus de Candolle in 1827 and was constructed by analogy with the terms "petal" and "sepal".

<span class="mw-page-title-main">Floral symmetry</span> Shape of flowers

Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts.

<span class="mw-page-title-main">Plant reproductive morphology</span> Parts of plant enabling sexual reproduction

Plant reproductive morphology is the study of the physical form and structure of those parts of plants directly or indirectly concerned with sexual reproduction.

<span class="mw-page-title-main">Perianth</span> Collective term for the sepals and petals, or either of them if one is absent

The perianth 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) or tepals when called a perigone. The term perianth is derived from Greek περί and άνθος, while perigonium is derived from περί and γόνος . In the mosses and liverworts (Marchantiophyta), the perianth is the sterile tubelike tissue that surrounds the female reproductive structure.

<span class="mw-page-title-main">Entomophily</span> Form of pollination by insects

Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of flowering plants, is distributed by insects. Flowers pollinated by insects typically advertise themselves with bright colours, sometimes with conspicuous patterns leading to rewards of pollen and nectar; they may also have an attractive scent which in some cases mimics insect pheromones. Insect pollinators such as bees have adaptations for their role, such as lapping or sucking mouthparts to take in nectar, and in some species also pollen baskets on their hind legs. This required the coevolution of insects and flowering plants in the development of pollination behaviour by the insects and pollination mechanisms by the flowers, benefiting both groups. Both the size and the density of a population are known to affect pollination and subsequent reproductive performance.

<span class="mw-page-title-main">Spikelet</span> Part of a spike inflorescence of a grass or sedge

A spikelet, in botany, describes the typical arrangement of the flowers of grasses, sedges and some other monocots.

<span class="mw-page-title-main">Nectar</span> Sugar-rich liquid produced by many flowering plants, that attracts pollinators and insects

Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide herbivore protection. Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, honeyeaters and bats. Nectar plays a crucial role in the foraging economics and evolution of nectar-eating species; for example, nectar foraging behavior is largely responsible for the divergent evolution of the African honey bee, A. m. scutellata and the western honey bee.

<span class="mw-page-title-main">Flower</span> Reproductive structure in flowering plants

A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.

<i>Antirrhinum majus</i> Species of flowering plant

Antirrhinum majus, the common snapdragon, is a species of flowering plant belonging to the genus Antirrhinum. The plant was placed in the family Plantaginaceae following a revision of its prior classical family, Scrophulariaceae.

<span class="mw-page-title-main">Pollination syndrome</span> Flower traits that attract pollinators

Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc.

Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.

<span class="mw-page-title-main">Papilionaceous flower</span> Butterfly-like flowers

Papilionaceous flowers are flowers with the characteristic irregular and butterfly-like corolla found in many, though not all, plants of the species-rich Faboideae subfamily of legumes. Tournefort suggested that the term Flores papilionacei originated with Valerius Cordus, who applied it to the flowers of the bean.

Floral biology is an area of ecological research that studies the evolutionary factors that have moulded the structures, behaviour and physiological aspects involved in the flowering of plants. The field is broad and interdisciplinary and involves research requiring expertise from multiple disciplines that can include botany, ethology, biochemistry, and entomology. A slightly narrower area of research within floral biology is sometimes called pollination biology or anthecology.

<span class="mw-page-title-main">Monocotyledon reproduction</span> Flowering plant reproduction system

The monocots are one of the two major groups of flowering plants, the other being the dicots. In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well. Despite these similarities and their close relatedness, monocots and dicots have distinct traits in their reproductive biologies.

Sexual selection is described as natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Sexual selection is a common concept in animal evolution but, with plants, it is oftentimes overlooked because many plants are hermaphrodites. Flowering plants show many characteristics that are often sexually selected for. For example, flower symmetry, nectar production, floral structure, and inflorescences are just a few of the many secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection in flowering plants.

<span class="mw-page-title-main">Pollination of orchids</span>

The pollination of orchids is a complex chapter in the biology of this family of plants that are distinguished by the complexity of their flowers and by intricate ecological interactions with their pollinator agents. It has captured the attention of numerous scientists over time, including Charles Darwin, father of the theory of evolution by natural selection. Darwin published in 1862 the first observations of the fundamental role of insects in orchid pollination, in his book The Fertilization of Orchids. Darwin stated that the varied stratagems orchids use to attract their pollinators transcend the imagination of any human being.

<span class="mw-page-title-main">Floral morphology</span> Study of flower structures

In botany, floral morphology is the study of the diversity of forms and structures presented by the flower, which, by definition, is a branch of limited growth that bears the modified leaves responsible for reproduction and protection of the gametes, called floral pieces.

<span class="mw-page-title-main">UV coloration in flowers</span> Natural phenomenon

UV coloration is a natural phenomenon that leads to unique interactions between organisms that have evolved the ability to perceive these wavelengths of light. It serves as one method to attract pollinators to the flower along with scent, shape, and nectar quality. Flowers are known for their range of visible colors that humans can see with their eyes and observe an array of different shades and patterns. The naked eye cannot see the ultraviolet coloration many flowers employ to bring attention to themselves. By either reflecting or absorbing UV light waves, flowers are able to communicate with pollinators. This allows plants that may require an animal pollinator to stand out from other flowers or distinguish where their flowers are in a muddied background of other plant parts. For the plant, it is important to share and receive pollen so they can reproduce, maintain their ecological role, and guide the evolutionary history of the population.

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