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[[Image:Phalaenopsis_%28aka%29.jpg|300px|thumb|A ''[[Phalaenopsis]]'' flower]]
[[Image:Blume mit Schmetterling und Biene 1uf.JPG|thumb|300px| [[Rudbeckia fulgida]]]]
A '''flower''', (<[[Old French]] ''flo(u)r''<[[Latin]] ''florem''<''flos''), also known as a '''bloom''' or '''blossom''', is the [[reproduction|reproductive]] structure found in [[flowering plant]]s ([[plant]]s of the division ''Magnoliophyta'', also called angiosperms). The flower's structure contains the plant's reproductive organs, and its function is to produce [[seed]]s. After [[fertilization]], portions of the flower develop into a [[fruit]] containing the seeds. For the higher plants, seeds are the next generation, and serve as the primary means by which individuals of a species are dispersed across the landscape. The grouping of flowers on a plant is called the [[inflorescence]].
In addition to serving as the reproductive organs of flowering plants, flowers have long been admired and used by [[human]]s, mainly to beautify their environment but also as a source of food.
==Function==
The biological function of a flower is to mediate the union of male and female [[gametes]] in order to produce [[seed]]s. The process begins with [[pollination]], is followed by [[fertilization]], and continues with the formation and [[Biological dispersal|dispersal]] of the seed.
==Morphology==
Flowering plants ''heterosporangiate'' (producing two types of reproductive [[spore]]s).
The [[pollen]] (male spores) and [[ovule]]s (female spores) are produced in different [[Organ (anatomy)|organs]], but the typical flower is a ''bisporangiate strobilus'' in that it contains both organs.
A flower is regarded as a modified [[Plant stem|stem]] with shortened internodes and bearing, at its [[node (botany)|nodes]], structures that may be highly modified [[leaf|leaves]].<ref>Eames, A. J. (1961) Morphology of the Angiosperms McGraw-Hill Book Co., New York.</ref> In essence, a flower structure forms on a modified shoot or ''axis'' with an apical [[meristem]] that does not grow continuously (growth is ''determinate''). The stem is called a [[pedicel]], the end of which is the ''torus'' or [[receptacle]]. The parts of a flower are arranged in [[whorl]]s on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:
[[Image:Sarracenia_flower_notitles.svg|thumb|300px|right|Anatomy of a ''[[Sarracenia]]'' flower. The umbrella shaped style is unique to this [[genus]], and will look different in most flowers]]
*''[[Calyx]]'' – the outer whorl of ''[[sepal]]s''; typically these are green, but are petal-like in some species.
*''[[Corolla]]'' – the whorl of ''[[petal]]s'', which are usually thin, soft and colored to attract insects that help the process of [[pollination]].
*''[[Androecium]]'' (from Greek ''andros oikia'': man's house) – one or two whorls of [[stamen]]s, each a [[filament]] topped by an [[anther]] where [[pollen]] is produced. Pollen contains the male [[gamete]]s.
*''[[Gynoecium]]'' (from Greek ''gynaikos oikia'': woman's house) – one or more [[pistil]]s. The female reproductive organ is the [[carpel]]: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called ''apocarpous''). The sticky tip of the pistil, the [[stigma]], is the receptor of pollen. The supportive stalk, the style becomes the pathway for [[pollen tube]]s to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.
Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. For example, the two subclasses of flowering pla
nts may be distinguished by the number of floral organs in each whorl: [[dicotyledon]]s typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and [[monocotyledon]]s having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.
[[Image:Crateva_religiosa.jpg|thumb|left|This ''[[Crateva religiosa]]'' flower is perfect: it has both stamens (outer ring) and a pistil (center)]]
In the majority of species individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being ''perfect'', ''bisexual'', or ''[[hermaphrodite]]''. However, in some species of plants the flowers are ''imperfect'' or ''unisexual'': having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female the species is regarded as ''[[Plant sexuality|dioecious]]''. However, where unisexual male and female flowers appear on the same plant, the species is considered ''[[Plant sexuality|monoecious]]''.
Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis—so-called ''composite flowers''— the collection of flowers is termed an ''[[inflorescence]]''; this term can also refer to the specific arrangements of flowers on a stem. In this regard, care must be exercised in considering what a ‘‘flower’’ is. In botanical terminology, a single [[daisy]] or [[sunflower]] for example, is not a flower but a flower ''[[head (botany)|head]]''—an inflorescence composed of numerous tiny flowers (sometimes called florets). Each of these flowers may be anatomically as described above. Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced - the flower is called regular or actinomorphic e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic. e.g. snapdragon or most orchids.
=== Floral formula ===
A ''floral formula'' is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant [[family (biology)|family]] rather than a particular species. The following representations are used:
'''Ca''' = calyx (sepal whorl; e.g. Ca<sup>5</sup> = 5 sepals)<br>
'''Co''' = corolla (petal whorl; e.g., Co<sup>3(x)</sup> = petals some multiple of three )<br>
'''Z''' = add if ''zygomorphic'' (e.g., CoZ<sup>6</sup> = zygomorphic with 6 petals)<br>
'''A''' = ''androecium'' (whorl of stamens; e.g., A<sup>∞</sup> = many stamens)<br>
'''G''' = ''gynoecium'' (carpel or carpels; e.g., G<sup>1</sup> = monocarpous)<br>
''x'' - to represent a "variable number"<br>
∞ - to represent "many"<br>
A floral formula would appear something like this:
:'''Ca<sup>5</sup>Co<sup>5</sup>A<sup>10 - ∞</sup>G<sup>1</sup>'''
Several additional symbols are sometimes used (see [http://botit.botany.wisc.edu/courses/systematics/key.html]).
==Pollination==
[[Image:Bees_Collecting_Pollen_cropped.jpg|right|thumb|200px|Grains of pollen sticking to this bee will be transfered to the next flower it visits]]
{{main|pollination}}
The primary purpose of a flower is to join the pollen of one plant with the ovules of another (or in some cases its own ovules) in order to form seed which is genetically unique, allowing for [[adaptation]] to occur. As such, each flower has a specific design which best encourages the transfer of this pollen. Many flowers are dependent upon the wind to move pollen between flowers of the same species. Others rely on animals (especially [[insect]]s) to accomplish this feat. Even large animals such as birds, bats, and [[pygmy possum]]s can be employed. The period of time during which this pr
ocess can take place (the flower is fully expanded and functional) is called ''anthesis''.
===Attraction methods===
[[Image:Ophrys_apifera_flower1.jpg|thumb|left|[[Ophrys apifera|Bee orchid]] mimics a female bee in order to attract a male bee pollinator]]
Many flowers in nature have evolved to attract animals to pollinate the flower, the movements of the pollinating agent contributing to the opportunity for genetic recombination within a dispersed plant population. Flowers that are insect-pollinated are called ''entomophilous'' (literally "insect-loving"). Flowers commonly have glands called ''nectaries'' on their various parts that attract these animals. [[Bird]]s and [[bee]]s are common [[pollinator]]s: both having color vision, thus opting for "colorful" flowers. Some flowers have patterns, called [[nectar guide]]s, that show pollinators where to look for nectar; they may be visible to us or only under [[ultraviolet]] light, which is visible to bees and some other insects. Flowers also attract pollinators by [[odor|scent]]. Many of their scents are pleasant to our sense of smell, but not all. Some plants, such as ''[[Rafflesia]]'', the [[titan arum]], and the North American [[pawpaw]] (''Asimina triloba''), are pollinated by [[fly|flies]], so produce a scent [[Carrion flower|imitating rotting meat]]. Flowers pollinated by night visitors such as bats or moths are especially likely to concentrate on scent - which can attract pollinators in the dark - rather than color: most such flowers are white.
Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Male bees move from one such flower to another in search of a mate.
===Pollination mechanism===
The pollination mechanism employed by a plant depends on what method of pollination is desired.
Entomophilous flowers (those which employ insects to transfer pollen) 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. Many flower rely on simple proximity between flower parts to ensure pollination. Others, such as the ''[[Sarracenia#Flowers|Sarracenia]]'' or [[Lady's Slipper|lady-slipper orchid]]s, have elaborate designs to ensure pollination while preventing [[self-pollination]].
The flowers of other species are pollinated by the wind (for example, [[Poaceae|grasses]]); they have no need to attract pollinators and therefore tend not to be "showy". Wind-pollinated flowers are referred to as ''anemophilous''. 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 [[insect]]s, 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.
<!--Not sure where to stick this info from the old article yet.
There is much confusion about the role of flowers in allergies. For example the showy and entomophilous [[goldenrod]] (''Solidago'') is frequently blamed for [[hay fever|respiratory allergies]], of which it is innocent, since its pollen cannot be airborne. Instead the [[allergen]] is usually the pollen of the contemporary bloom of anemophilous [[ragweed]] (''Ambrosia''), which can drift for many kilometers.-->
===Flower-pollinator relationships===
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 polli
nator 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 species|endangered plant species]] are so because of [[pollinator decline|shrinking pollinator populations]].
==Fertilization and dispersal==
{{main|biological dispersal}}
[[Image:Red Flower.JPG|thumb|200px|In this picture you can clearly see the stamens of the flower]]
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 [[dandelion]]s. 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 (see also: [[Plant sexuality]]).
==Evolution==
While land plants have existed for about 425 million years, the first ones [[plant sexuality|reproduced]] by a simple adaptation of their aquatic counterparts: [[spore]]s. In the sea, plants -- and some animals -- can simply scatter out little living copies of themselves to float away and grow elsewhere. This is how early plants, such as the modern fern, are thought to have reproduced. But plants soon began protecting these copies to deal with drying out and other abuse which is even more likely on land than in the sea. The protection became the [[seed]]...but not, yet, flowers. Early seed-bearing plants include the [[ginkgo]], [[conifer]]s (like pines), and [[fir]] trees. But the first fossil proof of actual flowers appears only 130 million years ago.
Unfortunately, there is no fossil evidence of exactly how flowers evolved; the evidence has them springing in advanced form into the fossil record. This was recognized almost immediately during the development of evolution theory, the strange appearance of flowers in the fossil record being called by [[Charles Darwin]] the Abominable Mystery.
[[Image:Flores.gif|200px|thumb|right|Various flower colors and shapes]]
[[Image:Syrphid fly on Virginia Bluebells.jpg|thumb|200px|A [[Syrphid fly]] on a [[Virginia Bluebell]]]]
The general assumption is that the function of flowers, from the start, was to involve other 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 wasp]]s 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 relationship]]s remain too fragile to survive competition with mainla
nd animals and spread, flowers proved to be an unusually effective means of production, spreading (whatever their actual origin) to become the dominant form of land plant life.
While there is only hard proof of such flowers existing about 130 million years ago, there is some circumstantial evidence that they did exist up to 250 million years ago. A chemical used by plants to defend their flowers, [[oleanane]], has been detected in fossil plants that old, including [[gigantopterid]]s[http://www.sciencedaily.com/releases/2001/04/010403071438.htm], 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 [[petrified wood|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[http://unisci.com/stories/20012/0615015.htm]. The most primitive flowers are thought to have had a variable number of flower parts, often separate from (but in contact with) each other. 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 (plants)|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".
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[http://www.livescience.com/othernews/050526_flower_power.html].
== Development ==
The molecular control of floral organ identity determination is fairly well understood. In a simple model, three gene activities interact in a combinatorial manner to determine the developmental identities of the organ primordia within the floral [[meristem]]. These gene functions are called A, B and C-gene functions. In the first floral whorl only A-genes are expressed, leading to the formation of sepals. In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. The model is based upon studies of [[homeotic]] mutants in Arabidopsis thaliana and snapdragon, Antirrhinum majus. For example, in a loss of B-gene function mutant flower we get sepals in the first whorl as usual, but also in the second whorl (the B-function lost that is needed for petal development). In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl. See also [[The ABC Model of Flower Development]].
Most genes central in this model belong to the [[MADS-box]] genes and are [[transcription factors]] that regulate the expression of the genes specific for each floral organ.
=== Flowering transition ===
The [[transition]] to flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that will ensure maximal [[reproductive]] success. To meet these needs a plant is able to interpret important endogenous and environmental cues such as changes in [[plant hormones]] levels and seasonable [[temperature]] and [[photoperiod]]changes. Many perennial and most biennial plants require [[vernalization]] to flower. The molecular interpretation of these signals throu
gh genes such as CONSTANS and FLC ensures that flowering occurs at a time that is favorable for [[fertilization]] and the formation of [[seeds]]<ref>Ausin et al (2005), Environmental regulation of flowering. Int J Dev Biol. 2005;49(5-6):689-705</ref>. Flower formation is initiated at the ends of stems, and involves a number of different physiological and morphological changes. The first step is the transformation of the vegetative stem primordia into floral primordia. This occurs as biochemical changes take place to change cellular differentiation of leaf, bud and stem tissues into tissue that will grow into the reproductive organs. Growth of the central part of the stem tip stops or flattens out and the sides develop protuberances in a whorled or spiral fashion around the outside of the stem end. These protuberances develop into the sepals, petals, stamens, and carpels. Once this process begins, in most plants, it cannot be reversed and the stems develop flowers, even if the initial start of the flower formation event was dependent of some environmental cue. Once the process begins, even if that cue is removed the stem will continue to develop a flower.
==Uses by humans==
===In everyday life===
[[Image:boysmellsflower.jpg|thumb|200px|Flowers are beloved for their various fragrances]]
In modern times, people have sought ways to cultivate, buy, wear, or just be around flowers and blooming plants, partly because of their agreeable [[smell]]. Around the world, people use flowers for a wide range of events and functions that, cumulatively, encompass one's lifetime:
* For new births or [[Christening]]s
* As a corsage or boutonniere to be worn at social functions or for holidays
* For [[wedding]] flowers for the bridal party, and decorations for the hall
* As brightening decorations within the home
* As a gift of remembrance for bon voyage parties, welcome home parties, and "thinking of you" gifts
* For [[funeral]] flowers and expressions of [[sympathy]] for the grieving
People therefore grow flowers around their homes, dedicate entire parts of their living space to [[flower garden]]s, pick wildflowers, or buy flowers from [[florist]]s who depend on an entire network of commercial growers and shippers to support their trade.
===Symbolism===
[[Image:Liliumbulbiferumflowertop.jpg|thumb|200px|right|Lilies are often used to denote life or resurrection]]
Many flowers have important [[symbol|symbolic]] meanings in Western culture. The practice of assigning meanings to flowers is known as [[floriography]]. Some of the more common examples include:
* Red [[rose]]s are given as a symbol of [[love]], beauty, and passion.
* [[Poppy|Poppies]] are a symbol of consolation in time of death. In the [[United Kingdom|UK]], [[Australia]] and [[Canada]], red poppies are worn to commemorate soldiers who have died in times of war.
* [[Iris (plant)|Irises]]/[[Lily]] are used in burials as a symbol referring to "resurrection/life". It is also associated with stars (sun) and its petals blooming/shining.
* [[Asteraceae|Daisies]] are a symbol of innocence.
Flowers within art are also representative of the female genitalia, as seen in the works of artists such as [[Georgia O'Keefe]], [[Imogen Cunningham]], [[Veronica Ruiz de Velasco]], and [[Judy Chicago]], and in fact in Asian and western classical art.
=== Edible flowers ===
Flowers provide less food than other major plants parts ([[seed]]s, [[fruit]]s, [[root]]s, [[plant stem|stem]]s and [[leaf|leaves]]) but they provide several important foods and [[spice]]s. Flower vegetables include [[broccoli]], [[cauliflower]] and [[artichoke]]. The most expensive spice, [[saffron]], consists of dried stigmas of a [[crocus]]. Other flower spices are [[clove]]s and [[caper]]s. [[Hops]] flowers are used to flavor [[beer]]. [[Marigold]] flowers are fed to [[chicken]]s to give their egg yolks a golden yellow color, which consumers find more desirable. [[Dandelion]] flowers are often made into wine. Bee [[Pollen]], pollen collected from bees, is considered a health food by some people. [[Honey]] consists of
bee-processed flower nectar and is often named for the type of flower, e.g. [[orange (fruit)|orange]] blossom honey, [[clover]] honey and [[tupelo]] honey.
Hundreds of fresh flowers are edible but few are widely marketed as food. They are often used to add color and flavor to salads. [[Squash (fruit)|Squash]] flowers are dipped in breadcrumbs and fried. Edible flowers include [[nasturtium]], [[chrysanthemum]], [[carnation]], [[cattail]], [[honeysuckle]], [[chicory]], [[cornflower]], [[Canna (plant)|Canna]], and [[sunflower]]. Some edible flowers are sometimes candied such as [[daisy]] and [[rose]] (you may also come across a candied [[pansy]]).
===Floristry===
''Under Construction'' <br>
''Main and related articles at'': [[Floristry]], [[Flower garden]], [[Gardening]], and [[List of flowers]]
Flowers can also be made into tea. Dried flowers such as chrysanthemum, rose, jasmine are infused into tea by the oriental people both for their fragrance and medical properties. Sometimes, they are also mixed with tea leaves for the added fragrance.
===In the arts===
[[Image:Ambrosius_Bosschaert,_the_Elder_04.jpg|thumb|200px|Flowers are common subjects of still lifes, such as this one by [[Ambrosius_Bosschaert the Elder]]]]
The great variety of delicate and beautiful flowers has inspired the works of numerous poets, especially from the 18<sup>th</sup>-19<sup>th</sup> century [[Romantic poetry|Romantic]] era. Famous examples include [[William Wordsworth]]'s ''[[I Wandered Lonely as a Cloud]]'' and [[William Blake]]'s ''Ah! Sun-Flower''.
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 [[Vincent van Gogh|Van Gogh]]'s [[sunflowers (series of paintings)|sunflowers]] series or [[Claude Monet|Monet]]'s water lilies.
===Mythology===
The Roman goddess of flowers, gardens, and the season of Spring is [[Flora (goddess)|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[http://www.bbc.co.uk/religion/religions/hinduism/deities/vishnu.shtml]. Apart from the association with [[Vishnu]], the Hindu tradition also considers the lotus to have spiritual significance[http://www.theflowerexpert.com/content/miscellaneous/flowers-and-religion]. For example, it figures in the Hindu stories of creation[http://www.theosociety.org/pasadena/sunrise/49-99-0/ge-mrook.htm].
==References==
<references />
* Eames, A. J. (1961) ''Morphology of the Angiosperms'' McGraw-Hill Book Co., New York.
* Esau, Katherine (1965) ''Plant Anatomy'' (2nd ed.) John Wiley & Sons, New York.
==See also==
{{commonscat|Flowers}}
{{Commons|Flower}}
{{wiktionary}}
* [[Plants]]
* [[Garden]]
* [[:Category:Gardening|Gardening]]
* [[Sowing]]
==External links==
{{SpamD|{{cleanup-spam}}}}
*[http://www.britannica.com/search?query=flower Britannica Online] Flower
{{SpamD|*[http://www.flowerpossibilities.com/encyclopedia.html Flower Encyclopedia]|}}
*[http://www.orchidean.com/videos Orchid Videos]
*[http://www.flowers-photos.eu flowers-photos.eu] Wild flowers photos
{{SpamD|*[http://www.conservatoryofflowers.org/ Conservatory of Flowers] |}}
* [http://wildflower.utexas.edu/ Native Plant Information Network]
[[Category:Flowers|*]]
[[Category:Gardening]]
[[Category:plant morphology]]
[[Category:Reproductive system]]
[[Category:Pollination]]
[[Image:Blume mit Schmetterling und Biene 1uf.JPG|thumb|300px| [[Rudbeckia fulgida]]]]
A '''flower''', (<[[Old French]] ''flo(u)r''<[[Latin]] ''florem''<''flos''), also known as a '''bloom''' or '''blossom''', is the [[reproduction|reproductive]] structure found in [[flowering plant]]s ([[plant]]s of the division ''Magnoliophyta'', also called angiosperms). The flower's structure contains the plant's reproductive organs, and its function is to produce [[seed]]s. After [[fertilization]], portions of the flower develop into a [[fruit]] containing the seeds. For the higher plants, seeds are the next generation, and serve as the primary means by which individuals of a species are dispersed across the landscape. The grouping of flowers on a plant is called the [[inflorescence]].
In addition to serving as the reproductive organs of flowering plants, flowers have long been admired and used by [[human]]s, mainly to beautify their environment but also as a source of food.
==Function==
The biological function of a flower is to mediate the union of male and female [[gametes]] in order to produce [[seed]]s. The process begins with [[pollination]], is followed by [[fertilization]], and continues with the formation and [[Biological dispersal|dispersal]] of the seed.
==Morphology==
Flowering plants ''heterosporangiate'' (producing two types of reproductive [[spore]]s).
The [[pollen]] (male spores) and [[ovule]]s (female spores) are produced in different [[Organ (anatomy)|organs]], but the typical flower is a ''bisporangiate strobilus'' in that it contains both organs.
A flower is regarded as a modified [[Plant stem|stem]] with shortened internodes and bearing, at its [[node (botany)|nodes]], structures that may be highly modified [[leaf|leaves]].<ref>Eames, A. J. (1961) Morphology of the Angiosperms McGraw-Hill Book Co., New York.</ref> In essence, a flower structure forms on a modified shoot or ''axis'' with an apical [[meristem]] that does not grow continuously (growth is ''determinate''). The stem is called a [[pedicel]], the end of which is the ''torus'' or [[receptacle]]. The parts of a flower are arranged in [[whorl]]s on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:
[[Image:Sarracenia_flower_notitles.svg|thumb|300px|right|Anatomy of a ''[[Sarracenia]]'' flower. The umbrella shaped style is unique to this [[genus]], and will look different in most flowers]]
*''[[Calyx]]'' – the outer whorl of ''[[sepal]]s''; typically these are green, but are petal-like in some species.
*''[[Corolla]]'' – the whorl of ''[[petal]]s'', which are usually thin, soft and colored to attract insects that help the process of [[pollination]].
*''[[Androecium]]'' (from Greek ''andros oikia'': man's house) – one or two whorls of [[stamen]]s, each a [[filament]] topped by an [[anther]] where [[pollen]] is produced. Pollen contains the male [[gamete]]s.
*''[[Gynoecium]]'' (from Greek ''gynaikos oikia'': woman's house) – one or more [[pistil]]s. The female reproductive organ is the [[carpel]]: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called ''apocarpous''). The sticky tip of the pistil, the [[stigma]], is the receptor of pollen. The supportive stalk, the style becomes the pathway for [[pollen tube]]s to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.
Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. For example, the two subclasses of flowering pla
nts may be distinguished by the number of floral organs in each whorl: [[dicotyledon]]s typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and [[monocotyledon]]s having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.
[[Image:Crateva_religiosa.jpg|thumb|left|This ''[[Crateva religiosa]]'' flower is perfect: it has both stamens (outer ring) and a pistil (center)]]
In the majority of species individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being ''perfect'', ''bisexual'', or ''[[hermaphrodite]]''. However, in some species of plants the flowers are ''imperfect'' or ''unisexual'': having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female the species is regarded as ''[[Plant sexuality|dioecious]]''. However, where unisexual male and female flowers appear on the same plant, the species is considered ''[[Plant sexuality|monoecious]]''.
Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis—so-called ''composite flowers''— the collection of flowers is termed an ''[[inflorescence]]''; this term can also refer to the specific arrangements of flowers on a stem. In this regard, care must be exercised in considering what a ‘‘flower’’ is. In botanical terminology, a single [[daisy]] or [[sunflower]] for example, is not a flower but a flower ''[[head (botany)|head]]''—an inflorescence composed of numerous tiny flowers (sometimes called florets). Each of these flowers may be anatomically as described above. Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced - the flower is called regular or actinomorphic e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic. e.g. snapdragon or most orchids.
=== Floral formula ===
A ''floral formula'' is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant [[family (biology)|family]] rather than a particular species. The following representations are used:
'''Ca''' = calyx (sepal whorl; e.g. Ca<sup>5</sup> = 5 sepals)<br>
'''Co''' = corolla (petal whorl; e.g., Co<sup>3(x)</sup> = petals some multiple of three )<br>
'''Z''' = add if ''zygomorphic'' (e.g., CoZ<sup>6</sup> = zygomorphic with 6 petals)<br>
'''A''' = ''androecium'' (whorl of stamens; e.g., A<sup>∞</sup> = many stamens)<br>
'''G''' = ''gynoecium'' (carpel or carpels; e.g., G<sup>1</sup> = monocarpous)<br>
''x'' - to represent a "variable number"<br>
∞ - to represent "many"<br>
A floral formula would appear something like this:
:'''Ca<sup>5</sup>Co<sup>5</sup>A<sup>10 - ∞</sup>G<sup>1</sup>'''
Several additional symbols are sometimes used (see [http://botit.botany.wisc.edu/courses/systematics/key.html]).
==Pollination==
[[Image:Bees_Collecting_Pollen_cropped.jpg|right|thumb|200px|Grains of pollen sticking to this bee will be transfered to the next flower it visits]]
{{main|pollination}}
The primary purpose of a flower is to join the pollen of one plant with the ovules of another (or in some cases its own ovules) in order to form seed which is genetically unique, allowing for [[adaptation]] to occur. As such, each flower has a specific design which best encourages the transfer of this pollen. Many flowers are dependent upon the wind to move pollen between flowers of the same species. Others rely on animals (especially [[insect]]s) to accomplish this feat. Even large animals such as birds, bats, and [[pygmy possum]]s can be employed. The period of time during which this pr
ocess can take place (the flower is fully expanded and functional) is called ''anthesis''.
===Attraction methods===
[[Image:Ophrys_apifera_flower1.jpg|thumb|left|[[Ophrys apifera|Bee orchid]] mimics a female bee in order to attract a male bee pollinator]]
Many flowers in nature have evolved to attract animals to pollinate the flower, the movements of the pollinating agent contributing to the opportunity for genetic recombination within a dispersed plant population. Flowers that are insect-pollinated are called ''entomophilous'' (literally "insect-loving"). Flowers commonly have glands called ''nectaries'' on their various parts that attract these animals. [[Bird]]s and [[bee]]s are common [[pollinator]]s: both having color vision, thus opting for "colorful" flowers. Some flowers have patterns, called [[nectar guide]]s, that show pollinators where to look for nectar; they may be visible to us or only under [[ultraviolet]] light, which is visible to bees and some other insects. Flowers also attract pollinators by [[odor|scent]]. Many of their scents are pleasant to our sense of smell, but not all. Some plants, such as ''[[Rafflesia]]'', the [[titan arum]], and the North American [[pawpaw]] (''Asimina triloba''), are pollinated by [[fly|flies]], so produce a scent [[Carrion flower|imitating rotting meat]]. Flowers pollinated by night visitors such as bats or moths are especially likely to concentrate on scent - which can attract pollinators in the dark - rather than color: most such flowers are white.
Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Male bees move from one such flower to another in search of a mate.
===Pollination mechanism===
The pollination mechanism employed by a plant depends on what method of pollination is desired.
Entomophilous flowers (those which employ insects to transfer pollen) 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. Many flower rely on simple proximity between flower parts to ensure pollination. Others, such as the ''[[Sarracenia#Flowers|Sarracenia]]'' or [[Lady's Slipper|lady-slipper orchid]]s, have elaborate designs to ensure pollination while preventing [[self-pollination]].
The flowers of other species are pollinated by the wind (for example, [[Poaceae|grasses]]); they have no need to attract pollinators and therefore tend not to be "showy". Wind-pollinated flowers are referred to as ''anemophilous''. 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 [[insect]]s, 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.
<!--Not sure where to stick this info from the old article yet.
There is much confusion about the role of flowers in allergies. For example the showy and entomophilous [[goldenrod]] (''Solidago'') is frequently blamed for [[hay fever|respiratory allergies]], of which it is innocent, since its pollen cannot be airborne. Instead the [[allergen]] is usually the pollen of the contemporary bloom of anemophilous [[ragweed]] (''Ambrosia''), which can drift for many kilometers.-->
===Flower-pollinator relationships===
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 polli
nator 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 species|endangered plant species]] are so because of [[pollinator decline|shrinking pollinator populations]].
==Fertilization and dispersal==
{{main|biological dispersal}}
[[Image:Red Flower.JPG|thumb|200px|In this picture you can clearly see the stamens of the flower]]
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 [[dandelion]]s. 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 (see also: [[Plant sexuality]]).
==Evolution==
While land plants have existed for about 425 million years, the first ones [[plant sexuality|reproduced]] by a simple adaptation of their aquatic counterparts: [[spore]]s. In the sea, plants -- and some animals -- can simply scatter out little living copies of themselves to float away and grow elsewhere. This is how early plants, such as the modern fern, are thought to have reproduced. But plants soon began protecting these copies to deal with drying out and other abuse which is even more likely on land than in the sea. The protection became the [[seed]]...but not, yet, flowers. Early seed-bearing plants include the [[ginkgo]], [[conifer]]s (like pines), and [[fir]] trees. But the first fossil proof of actual flowers appears only 130 million years ago.
Unfortunately, there is no fossil evidence of exactly how flowers evolved; the evidence has them springing in advanced form into the fossil record. This was recognized almost immediately during the development of evolution theory, the strange appearance of flowers in the fossil record being called by [[Charles Darwin]] the Abominable Mystery.
[[Image:Flores.gif|200px|thumb|right|Various flower colors and shapes]]
[[Image:Syrphid fly on Virginia Bluebells.jpg|thumb|200px|A [[Syrphid fly]] on a [[Virginia Bluebell]]]]
The general assumption is that the function of flowers, from the start, was to involve other 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 wasp]]s 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 relationship]]s remain too fragile to survive competition with mainla
nd animals and spread, flowers proved to be an unusually effective means of production, spreading (whatever their actual origin) to become the dominant form of land plant life.
While there is only hard proof of such flowers existing about 130 million years ago, there is some circumstantial evidence that they did exist up to 250 million years ago. A chemical used by plants to defend their flowers, [[oleanane]], has been detected in fossil plants that old, including [[gigantopterid]]s[http://www.sciencedaily.com/releases/2001/04/010403071438.htm], 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 [[petrified wood|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[http://unisci.com/stories/20012/0615015.htm]. The most primitive flowers are thought to have had a variable number of flower parts, often separate from (but in contact with) each other. 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 (plants)|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".
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[http://www.livescience.com/othernews/050526_flower_power.html].
== Development ==
The molecular control of floral organ identity determination is fairly well understood. In a simple model, three gene activities interact in a combinatorial manner to determine the developmental identities of the organ primordia within the floral [[meristem]]. These gene functions are called A, B and C-gene functions. In the first floral whorl only A-genes are expressed, leading to the formation of sepals. In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. The model is based upon studies of [[homeotic]] mutants in Arabidopsis thaliana and snapdragon, Antirrhinum majus. For example, in a loss of B-gene function mutant flower we get sepals in the first whorl as usual, but also in the second whorl (the B-function lost that is needed for petal development). In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl. See also [[The ABC Model of Flower Development]].
Most genes central in this model belong to the [[MADS-box]] genes and are [[transcription factors]] that regulate the expression of the genes specific for each floral organ.
=== Flowering transition ===
The [[transition]] to flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that will ensure maximal [[reproductive]] success. To meet these needs a plant is able to interpret important endogenous and environmental cues such as changes in [[plant hormones]] levels and seasonable [[temperature]] and [[photoperiod]]changes. Many perennial and most biennial plants require [[vernalization]] to flower. The molecular interpretation of these signals throu
gh genes such as CONSTANS and FLC ensures that flowering occurs at a time that is favorable for [[fertilization]] and the formation of [[seeds]]<ref>Ausin et al (2005), Environmental regulation of flowering. Int J Dev Biol. 2005;49(5-6):689-705</ref>. Flower formation is initiated at the ends of stems, and involves a number of different physiological and morphological changes. The first step is the transformation of the vegetative stem primordia into floral primordia. This occurs as biochemical changes take place to change cellular differentiation of leaf, bud and stem tissues into tissue that will grow into the reproductive organs. Growth of the central part of the stem tip stops or flattens out and the sides develop protuberances in a whorled or spiral fashion around the outside of the stem end. These protuberances develop into the sepals, petals, stamens, and carpels. Once this process begins, in most plants, it cannot be reversed and the stems develop flowers, even if the initial start of the flower formation event was dependent of some environmental cue. Once the process begins, even if that cue is removed the stem will continue to develop a flower.
==Uses by humans==
===In everyday life===
[[Image:boysmellsflower.jpg|thumb|200px|Flowers are beloved for their various fragrances]]
In modern times, people have sought ways to cultivate, buy, wear, or just be around flowers and blooming plants, partly because of their agreeable [[smell]]. Around the world, people use flowers for a wide range of events and functions that, cumulatively, encompass one's lifetime:
* For new births or [[Christening]]s
* As a corsage or boutonniere to be worn at social functions or for holidays
* For [[wedding]] flowers for the bridal party, and decorations for the hall
* As brightening decorations within the home
* As a gift of remembrance for bon voyage parties, welcome home parties, and "thinking of you" gifts
* For [[funeral]] flowers and expressions of [[sympathy]] for the grieving
People therefore grow flowers around their homes, dedicate entire parts of their living space to [[flower garden]]s, pick wildflowers, or buy flowers from [[florist]]s who depend on an entire network of commercial growers and shippers to support their trade.
===Symbolism===
[[Image:Liliumbulbiferumflowertop.jpg|thumb|200px|right|Lilies are often used to denote life or resurrection]]
Many flowers have important [[symbol|symbolic]] meanings in Western culture. The practice of assigning meanings to flowers is known as [[floriography]]. Some of the more common examples include:
* Red [[rose]]s are given as a symbol of [[love]], beauty, and passion.
* [[Poppy|Poppies]] are a symbol of consolation in time of death. In the [[United Kingdom|UK]], [[Australia]] and [[Canada]], red poppies are worn to commemorate soldiers who have died in times of war.
* [[Iris (plant)|Irises]]/[[Lily]] are used in burials as a symbol referring to "resurrection/life". It is also associated with stars (sun) and its petals blooming/shining.
* [[Asteraceae|Daisies]] are a symbol of innocence.
Flowers within art are also representative of the female genitalia, as seen in the works of artists such as [[Georgia O'Keefe]], [[Imogen Cunningham]], [[Veronica Ruiz de Velasco]], and [[Judy Chicago]], and in fact in Asian and western classical art.
=== Edible flowers ===
Flowers provide less food than other major plants parts ([[seed]]s, [[fruit]]s, [[root]]s, [[plant stem|stem]]s and [[leaf|leaves]]) but they provide several important foods and [[spice]]s. Flower vegetables include [[broccoli]], [[cauliflower]] and [[artichoke]]. The most expensive spice, [[saffron]], consists of dried stigmas of a [[crocus]]. Other flower spices are [[clove]]s and [[caper]]s. [[Hops]] flowers are used to flavor [[beer]]. [[Marigold]] flowers are fed to [[chicken]]s to give their egg yolks a golden yellow color, which consumers find more desirable. [[Dandelion]] flowers are often made into wine. Bee [[Pollen]], pollen collected from bees, is considered a health food by some people. [[Honey]] consists of
bee-processed flower nectar and is often named for the type of flower, e.g. [[orange (fruit)|orange]] blossom honey, [[clover]] honey and [[tupelo]] honey.
Hundreds of fresh flowers are edible but few are widely marketed as food. They are often used to add color and flavor to salads. [[Squash (fruit)|Squash]] flowers are dipped in breadcrumbs and fried. Edible flowers include [[nasturtium]], [[chrysanthemum]], [[carnation]], [[cattail]], [[honeysuckle]], [[chicory]], [[cornflower]], [[Canna (plant)|Canna]], and [[sunflower]]. Some edible flowers are sometimes candied such as [[daisy]] and [[rose]] (you may also come across a candied [[pansy]]).
===Floristry===
''Under Construction'' <br>
''Main and related articles at'': [[Floristry]], [[Flower garden]], [[Gardening]], and [[List of flowers]]
Flowers can also be made into tea. Dried flowers such as chrysanthemum, rose, jasmine are infused into tea by the oriental people both for their fragrance and medical properties. Sometimes, they are also mixed with tea leaves for the added fragrance.
===In the arts===
[[Image:Ambrosius_Bosschaert,_the_Elder_04.jpg|thumb|200px|Flowers are common subjects of still lifes, such as this one by [[Ambrosius_Bosschaert the Elder]]]]
The great variety of delicate and beautiful flowers has inspired the works of numerous poets, especially from the 18<sup>th</sup>-19<sup>th</sup> century [[Romantic poetry|Romantic]] era. Famous examples include [[William Wordsworth]]'s ''[[I Wandered Lonely as a Cloud]]'' and [[William Blake]]'s ''Ah! Sun-Flower''.
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 [[Vincent van Gogh|Van Gogh]]'s [[sunflowers (series of paintings)|sunflowers]] series or [[Claude Monet|Monet]]'s water lilies.
===Mythology===
The Roman goddess of flowers, gardens, and the season of Spring is [[Flora (goddess)|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[http://www.bbc.co.uk/religion/religions/hinduism/deities/vishnu.shtml]. Apart from the association with [[Vishnu]], the Hindu tradition also considers the lotus to have spiritual significance[http://www.theflowerexpert.com/content/miscellaneous/flowers-and-religion]. For example, it figures in the Hindu stories of creation[http://www.theosociety.org/pasadena/sunrise/49-99-0/ge-mrook.htm].
==References==
<references />
* Eames, A. J. (1961) ''Morphology of the Angiosperms'' McGraw-Hill Book Co., New York.
* Esau, Katherine (1965) ''Plant Anatomy'' (2nd ed.) John Wiley & Sons, New York.
==See also==
{{commonscat|Flowers}}
{{Commons|Flower}}
{{wiktionary}}
* [[Plants]]
* [[Garden]]
* [[:Category:Gardening|Gardening]]
* [[Sowing]]
==External links==
{{SpamD|{{cleanup-spam}}}}
*[http://www.britannica.com/search?query=flower Britannica Online] Flower
{{SpamD|*[http://www.flowerpossibilities.com/encyclopedia.html Flower Encyclopedia]|}}
*[http://www.orchidean.com/videos Orchid Videos]
*[http://www.flowers-photos.eu flowers-photos.eu] Wild flowers photos
{{SpamD|*[http://www.conservatoryofflowers.org/ Conservatory of Flowers] |}}
* [http://wildflower.utexas.edu/ Native Plant Information Network]
[[Category:Flowers|*]]
[[Category:Gardening]]
[[Category:plant morphology]]
[[Category:Reproductive system]]
[[Category:Pollination]]
