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Flower

2007 Schools Wikipedia Selection. Related subjects: Plants

   Clivia miniata A cluster of flowers (Clivia miniata)
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   Clivia miniata A cluster of flowers (Clivia miniata)
   A Blue Summer Flower.
   Enlarge
   A Blue Summer Flower.

   A flower, (< Old French flo(u)r<Latin florem<flos), also known as a
   bloom or blossom, is the reproductive structure found in flowering
   plants (plants of the division Magnoliophyta, also called angiosperms).
   The flower structure contains the plant's reproductive organs, and its
   function is to produce seeds through reproduction. 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.
   After fertilization, portions of the flower develop into a fruit
   containing the seeds.

Flower function

   The function of a flower is to mediate the union of male and female
   gametes in order to produce seeds. The process begins with pollination,
   is followed by fertilization, and continues with the formation and
   dispersal of the seed.

Flower anatomy

   Flowering plants heterosporangiate (producing two types of reproductive
   spores). The pollen (male spores) and ovules (female spores) are
   produced in different organs, but the typical flower is a bisporangiate
   strobilus in that it contains both organs.

   A flower is regarded as a modified stem (Eames, 1961) with shortened
   internodes and bearing, at its nodes, structures that may be highly
   modified leaves. 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
   whorls 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:
     * Calyx – the outer whorl of sepals; typically these are green, but
       are petal-like in some species.
     * Corolla – the whorl of petals, 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 stamens, each a filament topped by an anther where pollen
       is produced. Pollen contains the male gametes.
     * Gynoecium (from Greek gynaikos oikia: woman's house) – one or more
       pistils. 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 tubes to grow from
       pollen grains adhering to the stigma, to the ovules, carrying the
       reproductive material.

   The androecium and gynoecium of a tulip.
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   The androecium and gynoecium of a tulip.

   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 plants may be distinguished by the number of
   floral organs in each whorl: dicotyledons typically having 4 or 5
   organs (or a multiple of 4 or 5) in each whorl and monocotyledons
   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.

   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
   dioecious. However, where unisexual male and female flowers appear on
   the same plant, the species is considered monoecious.
   Close-up of a lily, showing six stamens and the stigma and style of a
   pistil.
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   Close-up of a lily, showing six stamens and the stigma and style of a
   pistil.

   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—an
   inflorescence composed of numerous tiny flowers (sometimes called
   florets). Each of these flowers may be anatomically as described above.

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 rather
   than a particular species. The following representations are used:

   Ca = calyx (sepal whorl; e.g. Ca^5 = 5 sepals)
   Co = corolla (petal whorl; e.g., Co^3(x) = petals some multiple of
   three )
       Z = add if zygomorphic (e.g., CoZ^6 = zygomorphic with 6 petals)
   A = androecium (whorl of stamens; e.g., A^∞ = many stamens)
   G = gynoecium (carpel or carpels; e.g., G^1 = monocarpous)

   x - to represent a "variable number"
   ∞ - to represent "many"

   A floral formula would appear something like this:

          Ca^5Co^5A^10 - ∞G^1

   Several other symbols are used that will have to await drawings to
   illustrate here (see ).

Pollination

   Grains of pollen sticking to this bee will be transfered to the next
   flower it visits
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   Grains of pollen sticking to this bee will be transfered to the next
   flower it visits

   Also see the main article on 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 insects) to accomplish this feat. 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.

Attraction methods

   This bee orchid mimics a female bee in order to attract a male bee
   pollinator
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   This 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. Birds and
   bees are common pollinators: both having colour vision, thus opting for
   "colorful" flowers. Some flowers have patterns, called nectar guides,
   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 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 flies, so produce a scent
   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 colour: 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 colour,
   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 or lady-slipper orchids, have elaborate designs to
   ensure pollination while preventing self-pollination.

   The flowers of other species are pollinated by the wind (for example,
   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 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.

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 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.

Fertilization

   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.
   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).

Seed production

Seed dispersal

Flower evolution

   While land plants have existed for about 425 million years, the first
   ones reproduced by a simple adaptation of their aquatic counterparts;
   spores. 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,
   conifers (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.

   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 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 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 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 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
   (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 .

Uses by humans

Edible flowers

   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. Marigold flowers are fed to chickens to give their
   skin a golden yellow colour, 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 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 colour and flavor to salads. Squash
   flowers are dipped in breadcrumbs and fried. Edible flowers include
   nasturtium, chrysanthemum, carnation, cattail, honeysuckle, chicory,
   cornflower and sunflower. Certain edible flowers are sometimes candied
   such as pansy, daisy and rose.

Horticulture and floristry

   Under Construction
   Main and related articles at: Floristry, Flower garden, Gardening,
   Horticulture, and List of flowers

Flowers in the arts

   Flowers are common subjects of still lifes, such as this one by
   Ambrosius_Bosschaert the Elder
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   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 many poets, especially from the Romantic era. Famous examples
   include and 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
   Van Gogh's sunflowers series or Monet's water lilies.

   The Roman goddess of flowers, gardens, and the season of Spring is
   Flora. The Greek goddess of spring, flowers and nature is Chloris.

Flowers in everyday life

   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 Christenings
     * 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 gardens, pick wildflowers, or buy
   flowers from florists who depend on an entire network of commercial
   growers and shippers to support their trade.

Flowers as symbols

   Lilies are often used to denote life or resurrection.
   Enlarge
   Lilies are often used to denote life or resurrection.

   Many flowers have important symbolic meanings in Western culture. The
   practice of assigning meanings to flowers is known as floriography.
   Some of the more common examples include:
     * Red roses are given as a symbol of love, beauty, and passion.
     * Poppies are a symbol of consolation in time of death. In the UK,
       Australia and Canada, red poppies are worn to commemorate soldiers
       who have died in times of war.
     * 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.
     * 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.

   Retrieved from " http://en.wikipedia.org/wiki/Flower"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
