Botanists describe these flowers as being perfect or bisexual and the species as hermaphroditic. Some flowers lack one or the other reproductive organ and called imperfect or unisexual. If unisex flowers are found on the same individual plant but in different locations, the species is said to be monoecious. If each type of unisex flower is found only on separate individuals, the plant is dioecious. Flowering plants usually face selective pressure to optimize the transfer of their pollen , and this is typically reflected in the morphology of the flowers and the behaviour of the plants.
Pollen may be transferred between plants via a number of 'vectors'. Others use biotic vectors including insects entomophily , birds ornithophily , bats chiropterophily or other animals. Some plants make use of multiple vectors, but many are highly specialised. Cleistogamous flowers are self-pollinated, after which they may or may not open. Many Viola and some Salvia species are known to have these types of flowers. The flowers of plants that make use of biotic pollen vectors commonly have glands called nectaries that act as an incentive for animals to visit the flower.
Some flowers have patterns, called nectar guides , that show pollinators where to look for nectar. Flowers also attract pollinators by scent and color. Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Flowers are also specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant such as nectar, pollen, or a mate.
In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits. Anemophilous flowers use the wind to move pollen from one flower to the next.
Examples include grasses, birch trees, ragweed and maples. They have no need to attract pollinators and therefore tend not to be "showy" flowers. Male and female reproductive organs are generally found in separate flowers, the male flowers having a number of long filaments terminating in exposed stamens, and the female flowers having long, feather-like stigmas. Whereas the pollen of animal-pollinated flowers tends to be large-grained, sticky, and rich in protein another "reward" for pollinators , anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to animals.
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The primary purpose of a flower is reproduction. Pollination is the movement of pollen from the anthers to the stigma. The joining of the sperm to the ovules is called fertilization. Normally pollen is moved from one plant to another, but many plants are able to self pollinate. The fertilized ovules produce seeds that are the next generation. Sexual reproduction produces genetically unique offspring, allowing for adaptation. Flowers have specific designs which encourages the transfer of pollen from one plant to another of the same species. Many plants are dependent upon external factors for pollination, including: Even large animals such as birds, bats, and pygmy possums can be employed.
The period of time during which this process can take place the flower is fully expanded and functional is called anthesis. The study of pollination by insects is called anthecology. Often they are specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant such as nectar, pollen, or a mate. Many flowers rely on simple proximity between flower parts to ensure pollination.
Others, such as the Sarracenia or lady-slipper orchids , have elaborate designs to ensure pollination while preventing self-pollination. They have no need to attract pollinators and therefore tend not to grow large blossoms. Whereas the pollen of entomophilous flowers tends to be large-grained, sticky, and rich in protein another "reward" for pollinators , anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to insects , though it may still be gathered in times of dearth.
Honeybees and bumblebees actively gather anemophilous corn maize pollen, though it is of little value to them. Some flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation. The extreme case of self-fertilization occurs in flowers that always self-fertilize, such as many dandelions. Some flowers are self-pollinated and use flowers that never open or are self-pollinated before the flowers open, these flowers are called cleistogamous.
Many Viola species and some Salvia have these types of flowers. Conversely, many species of plants have ways of preventing self-fertilization. Unisexual male and female flowers on the same plant may not appear or mature at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-sterile or self-incompatible. Plants cannot move from one location to another, thus many flowers have evolved to attract animals to transfer pollen between individuals in dispersed populations.
Flowers that are insect-pollinated are called entomophilous ; literally "insect-loving" in Greek. They can be highly modified along with the pollinating insects by co-evolution. Flowers commonly have glands called nectaries on various parts that attract animals looking for nutritious nectar. Birds and bees have color vision, enabling them to seek out "colorful" flowers. Some flowers have patterns, called nectar guides , that show pollinators where to look for nectar; they may be visible only under ultraviolet light, which is visible to bees and some other insects.
Flowers also attract pollinators by scent and some of those scents are pleasant to our sense of smell. Not all flower scents are appealing to humans; a number of flowers are pollinated by insects that are attracted to rotten flesh and have flowers that smell like dead animals, often called Carrion flowers , including Rafflesia , the titan arum , and the North American pawpaw Asimina triloba. Flowers pollinated by night visitors, including bats and moths, are likely to concentrate on scent to attract pollinators and most such flowers are white.
Other flowers use mimicry to attract pollinators. Male bees move from one such flower to another in search of a mate. Many flowers have close relationships with one or a few specific pollinating organisms. Many flowers, for example, attract only one specific species of insect, and therefore rely on that insect for successful reproduction. This close relationship is often given as an example of coevolution , as the flower and pollinator are thought to have developed together over a long period of time to match each other's needs. This close relationship compounds the negative effects of extinction.
The extinction of either member in such a relationship would mean almost certain extinction of the other member as well. Some endangered plant species are so because of shrinking pollinator populations. There is much confusion about the role of flowers in allergies.
For example, the showy and entomophilous goldenrod Solidago is frequently blamed for respiratory allergies , of which it is innocent, since its pollen cannot be airborne. The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants trees, grasses, and weeds that do not have showy flowers.
These plants make small, light, dry pollen grains that are custom-made for wind transport. The type of allergens in the pollen is the main factor that determines whether the pollen is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. It is, however, a relatively rare cause of allergy because the types of allergens in pine pollen appear to make it less allergenic. Instead the allergen is usually the pollen of the contemporary bloom of anemophilous ragweed Ambrosia , which can drift for many miles.
Scientists have collected samples of ragweed pollen miles out at sea and 2 miles high in the air. Among North American plants, weeds are the most prolific producers of allergenic pollen. It is common to hear people say they are allergic to colorful or scented flowers like roses.
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In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees. While land plants have existed for about million years, the first ones reproduced by a simple adaptation of their aquatic counterparts: In the sea, plants—and some animals—can simply scatter out genetic clones of themselves to float away and grow elsewhere.
This is how early plants reproduced. But plants soon evolved methods of protecting these copies to deal with drying out and other damage which is even more likely on land than in the sea. The protection became the seed , though it had not yet evolved the flower. Early seed-bearing plants include the ginkgo and conifers. Several groups of extinct gymnosperms, particularly seed ferns , have been proposed as the ancestors of flowering plants but there is no continuous fossil evidence showing exactly how flowers evolved. The apparently sudden appearance of relatively modern flowers in the fossil record posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin.
Recently discovered angiosperm fossils such as Archaefructus , along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. An early fossil of a flowering plant, Archaefructus liaoningensis from China, is dated about million years old.
Now, another plant million-year-old Montsechia vidalii , discovered in Spain takes the title of world's oldest flower from Archaefructus sinensis. Recent DNA analysis molecular systematics  shows that Amborella trichopoda , found on the Pacific island of New Caledonia, is the only species in the sister group to the rest of the flowering plants, and morphological studies suggest that it has features which may have been characteristic of the earliest flowering plants.
While there is only hard proof of such flowers about million years ago,   there is some circumstantial evidence of flowers as much as million years ago.
A chemical used by plants to defend their flowers, oleanane , has been detected in fossil plants that old, including gigantopterids ,  which evolved at that time and bear many of the traits of modern, flowering plants, though they are not known to be flowering plants themselves, because only their stems and prickles have been found preserved in detail; one of the earliest examples of petrification. The similarity in leaf and stem structure can be very important, because flowers are genetically just an adaptation of normal leaf and stem components on plants, a combination of genes normally responsible for forming new shoots.
The flowers would have tended to grow in a spiral pattern, to be bisexual in plants, this means both male and female parts on the same flower , and to be dominated by the ovary female part. As flowers grew more advanced, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant, or at least "ovary inferior". The general assumption is that the function of flowers, from the start, was to involve animals in the reproduction process. Pollen can be scattered without bright colors and obvious shapes, which would therefore be a liability, using the plant's resources, unless they provide some other benefit.
One proposed reason for the sudden, fully developed appearance of flowers is that they evolved in an isolated setting like an island, or chain of islands, where the plants bearing them were able to develop a highly specialized relationship with some specific animal a wasp, for example , the way many island species develop today. This symbiotic relationship, with a hypothetical wasp bearing pollen from one plant to another much the way fig wasps do today, could have eventually resulted in both the plant s and their partners developing a high degree of specialization.
Island genetics is believed to be a common source of speciation , especially when it comes to radical adaptations which seem to have required inferior transitional forms. Note that the wasp example is not incidental; bees, apparently evolved specifically for symbiotic plant relationships, are descended from wasps. Likewise, most fruit used in plant reproduction comes from the enlargement of parts of the flower. This fruit is frequently a tool which depends upon animals wishing to eat it, and thus scattering the seeds it contains.
While many such symbiotic relationships remain too fragile to survive competition with mainland organisms, flowers proved to be an unusually effective means of production, spreading whatever their actual origin to become the dominant form of land plant life. Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that many of them cannot be pollinated in nature.
Many modern, domesticated flowers used to be simple weeds, which only sprouted when the ground was disturbed. Some of them tended to grow with human crops, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection. Many flowering plants reflect as much light as possible within the range of visible wavelengths of the pollinator the plant intends to attract.
Flowers that reflect the full range of visible light are generally perceived as white by a human observer. An important feature of white flowers is that they reflect equally across the visible spectrum. While many flowering plants use white to attract pollinators, the use of color is also widespread even within the same species.
Color allows a flowering plant to be more specific about the pollinator it seeks to attract. The color model used by human color reproduction technology CMYK relies on the modulation of pigments that divide the spectrum into broad areas of absorption. Flowering plants by contrast are able to shift the transition point wavelength between absorption and reflection. If it is assumed that the visual systems of most pollinators view the visible spectrum as circular then it may be said that flowering plants produce color by absorbing the light in one region of the spectrum and reflecting the light in the other region.
With CMYK, color is produced as a function of the amplitude of the broad regions of absorption. Flowering plants by contrast produce color by modifying the frequency or rather wavelength of the light reflected. Most flowers absorb light in the blue to yellow region of the spectrum and reflect light from the green to red region of the spectrum. For many species of flowering plant, it is the transition point that characterizes the color that they produce. Color may be modulated by shifting the transition point between absorption and reflection and in this way a flowering plant may specify which pollinator it seeks to attract.
Some flowering plants also have a limited ability to modulate areas of absorption. This is typically not as precise as control over wavelength. Humans observers will perceive this as degrees of saturation the amount of white in the color.
Flower - Wikipedia
Many flowers have important symbolic meanings in Western culture. Some of the more common examples include:. Because of their varied and colorful appearance, flowers have long been a favorite subject of visual artists as well. Some of the most celebrated paintings from well-known painters are of flowers, such as Van Gogh 's sunflowers series or Monet 's water lilies.
Flowers are also dried, freeze dried and pressed in order to create permanent, three-dimensional pieces of flower art. Flowers within art are also representative of the female genitalia ,  as seen in the works of artists such as Georgia O'Keeffe , Imogen Cunningham , Veronica Ruiz de Velasco , and Judy Chicago , and in fact in Asian and western classical art. Many cultures around the world have a marked tendency to associate flowers with femininity. The great variety of delicate and beautiful flowers has inspired the works of numerous poets, especially from the 18th—19th century Romantic era.
Their symbolism in dreams has also been discussed, with possible interpretations including "blossoming potential". The Roman goddess of flowers, gardens, and the season of Spring is Flora. The Greek goddess of spring, flowers and nature is Chloris. In Hindu mythology, flowers have a significant status. Vishnu, one of the three major gods in the Hindu system, is often depicted standing straight on a lotus flower. In modern times people have sought ways to cultivate, buy, wear, or otherwise be around flowers and blooming plants, partly because of their agreeable appearance and smell.
People therefore grow flowers around their homes, dedicate entire parts of their living space to flower gardens , pick wildflowers, or buy flowers from florists who depend on an entire network of commercial growers and shippers to support their trade. Flowers provide less food than other major plants parts seeds , fruits , roots , stems and leaves but they provide several important foods and spices. Flower vegetables include broccoli , cauliflower and artichoke. The most expensive spice, saffron , consists of dried stigmas of a crocus. Other flower spices are cloves and capers.
Hops flowers are used to flavor beer. There are many different kinds of flowers in different areas in the world. Even in the coldest places, for example the Arctic , flowers can grow during a few months. Flowers may grow separately on the plant, or they may grow together in an inflorescence. To investigate the structure of a flower, it must be dissected , and its structure summarised by a floral diagram or a floral formula. Then its family can be identified with the aid of a flora , which is a book designed to help you identify plants. Although this arrangement is typical, plant species show a wide variation in floral structure.
Flowers are an important evolutionary advance made by flowering plants.
Some flowers are dependent upon the wind to move pollen between flowers of the same species. Their pollen grains are light-weight. Many others rely on insects or birds to move pollen. The role of flowers is to produce seeds , which are contained in fruit. Fruits and seeds are a means of dispersal. Plants do not move, but wind, animals and birds spread the plants across the landscape. Since the ovules are protected by carpels , it takes something special for fertilisation to happen.
Angiosperms have pollen grains comprising just three cells. One cell is responsible for drilling down through the integuments, and creating a passage for the two sperm cells to flow down. The megagametophyte  has just seven cells. Of these, one is the egg cell; it fuses with a sperm cell, forming the zygote. Another cell joins with the other sperm, and dedicates itself to forming a nutrient-rich endosperm.
The other cells take auxiliary roles. This process of "double fertilisation" is unique and common to all angiosperms. Flowers are modified leaves possessed only by the flowering plants angiosperms , which are relatively late to appear in the fossil record. The earliest known fossils of flowers and flowering plants are from million years ago, in the Lower Cretaceous. It has been concluded that the two clades diverged split some million years ago. Flowers have long been admired and used by humans.
Most people think that flowers are beautiful. Many people also love flowers for their fragrances scents. People enjoy seeing flowers growing in gardens. People also enjoy growing flowers in their backyards, outside their homes. People often wear flowers on their clothes or give flowers as a gift during special occasions, holidays, or rituals, such as the birth of a new baby or a Christening , at weddings marriages , at funerals when a person dies.
People often buy flowers from businesses called florists. Some parents name their girl children after a flower. Some common flower names are: