Flower
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Flowers, also known as blossoms and blooms, are the reproductive structures of flowering plants. Typically, they are structured in four circular levels around the end of a stalk. These include: sepals, which are modified leaves that support the flower; petals, often designed to attract pollinators; male stamens, where pollen is presented; and female gynoecia, where pollen is received and its movement is facilitated to the egg. When flowers are arranged in a group, they are known collectively as an inflorescence.
The development of flowers is a complex and important part in the life cycles of flowering plants. In most plants, flowers are able to produce sex cells of both sexes. Pollen, which can produce the male sex cells, is transported between the male and female parts of flowers in pollination. Pollination can occur between different plants, as in cross-pollination, or between flowers on the same plant or even the same flower, as in self-pollination. Pollen movement may be caused by animals, such as birds and insects, or non-living things like wind and water. The colour and structure of flowers assist in the pollination process.
After pollination, the sex cells are fused together in the process of fertilisation, which is a key step in sexual reproduction. Through cellular and nuclear divisions, the resulting cell grows into a seed, which contains structures to assist in the future plant's survival and growth. At the same time, the female part of the flower forms into a fruit, and the other floral structures die. The function of fruit is to protect the seed and aid in its dispersal away from the mother plant. Seeds can be dispersed by living things, such as birds who eat the fruit and distribute the seeds when they defecate. Non-living things like wind and water can also help to disperse the seeds.
Flowers first evolved between 150 and 190 million years ago, in the Jurassic. Plants with flowers replaced non-flowering plants in many ecosystems, as a result of flowers' superior reproductive effectiveness. In the study of plant classification, flowers are a key feature used to differentiate plants. For thousands of years humans have used flowers for a variety of other purposes, including: decoration, medicine, food, and perfumes. In human cultures, flowers are used symbolically and feature in art, literature, religious practices, ritual, and festivals. All aspects of flowers, including size, shape, colour, and smell, show immense diversity across flowering plants. They range in size from Script error: No such module "convert". to Script error: No such module "convert"., and in this way range from highly reduced and understated, to dominating the structure of the plant. Plants with flowers dominate the majority of the world's ecosystems, and themselves range from tiny orchids and major crop plants to large trees.
Etymology
In botany, flowers are defined as the reproductive structures of angiosperms (flowering plants),Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". while cones are regarded as the gymnosperm equivalent.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Template:Notetag Bloom is similarly defined, but may also be used to describe the collective of flowers on a plant, as in the phrase: covered with bloom.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flower is also commonly used to describe the whole of a plant that produces flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Flower entered Middle English via Old French Script error: No such module "Lang". from earlier Latin Script error: No such module "Lang"., Script error: No such module "Lang". and before that Proto-Italic Script error: No such module "Lang"., all of which had the same meaning 'flower'.[1]Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The spelling flour was more common in English until the 17th century, when it became specialised to mean "ground grain" — originally an instance of figurative flower meaning "best part; finest".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The Old English word for flower was blossom,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". which is still used today, but refers especially to the flowers of edible fruit trees, and not to the whole flowering plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flower, bloom, and blossom are all cognates and are derived from the Proto-Indo-European word Script error: No such module "Lang". ('blossoming').Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Both bloom and blossom refer to flowers as well as the state of flowering; as in the phrases: in bloom or in blossom.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Function
The main purpose of a flower is reproduction of the individual,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". aiding in the survival of the species.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers not only produce spores, which become gametophytes that produce sex cells, leading to fertilised cells, but also develop and help disseminate seeds.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Sexual reproduction between plants results in evolutionary adaptation, which improves species survival. Plants favour cross-pollination because it promotes the joining of sex cells from genetically distinct plants of the same species, thereby increasing genetic diversity. Facilitating this process is a key function of flowers and is often reflected in their form and structure.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Features designed to attract pollinators are among the most common adaptations.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
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Structure
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The structure of a flower, termed its morphology,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". can be considered in two parts: the vegetative part, consisting of non-reproductive structures such as petals; and the reproductive or sexual parts. A stereotypical, or complete,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". flower is made up of four kinds of structures arranged in sets called whorls. They grow around the tip of a short stalk or axis, called a receptacle.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The four main whorls (starting from the base of the flower and working upwards) are the calyx, petals, androecium, and gynoecium.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Vegetative
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The non-reproductive or vegetative part of the flower, known collectively as the perianth, consists of calyx (the modified outer leaves), and the petals. The receptacle is the thickened part of the flower stalk, called the pedicel, which supports all of the other flower structures.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Calyx
The sepals, collectively called the calyx, are modified leaves that occur on the outermost whorl of the flower. They are leaf-like,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". in that they have a broad base, pores, green pigment, and may have analogous outgrowths from the stem. Sepals are often waxy, tough, and grow quickly to protect the flower as it develops.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Although they sometimes fall off at maturity, sepals more commonly persist to protect the fruit and aid in its dispersal.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The sepals in some flowers may be partially or completely fused together.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Petals
The petals, collectively called the corolla,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". are almost or completely fibreless leaf-like structures that form the innermost whorl of the perianth. They are often delicate and thin and are usually coloured, shaped, or scented, to encourage and facilitate pollination.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The petals may be fused together.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Petals often feature UV patterns invisible to humans but visible to pollinators.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In some flowers, petals and sepals are indistinguishable from one another.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Reproductive
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All flowering plants are heterosporous, that is, every individual plant produces two types of spores. Spores are formed from mature plants, which contain two sets of chromosomes, and are divided into microspores and megaspores—the precursors to pollen and embryo sacs respectively. Pollen and embryo sacs are the male and female gametophytes, sex cell-producing structures, and contain just one set of chromosomes. Microspores are produced by meiosis inside anthers, the male part of flowers,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and megaspores are produced inside ovules contained within the ovary.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". As with all heterosporous plants, the gametophytes also develop inside the spores.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
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Diagram of anther in cross section. 1: Filament; 2: Theca; 3: Connective (conducting vessels in red); 4: Pollen sac
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Diagram of angiosperm ovule
Male
The androecium is the whorl of male parts called stamens, which produce pollen. Stamens consist typically of an anther, made up of four pollen sacs arranged in two sheaths called thecae, connected to a filament, or stalk.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The anther contains microspores which become pollen, the male gametophyte, after undergoing meiosis.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Although they exhibit the widest variation among floral organs,Template:Notetag the androecium is usually confined just to one whorl and to two whorls only in rare cases.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Female
The gynoecium, consisting of one or more carpels, is the female part of the flower and found on the innermost whorl.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Each carpel consists of: a stigma, which receives pollen; a style, the stalk; and an ovary, which contains the ovules, and the female gametophytes by extension. Carpels may be fused together and are often described collectively as a pistil. Inside the ovary, the ovules are attached to the placenta by structures called funiculi.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Variation
Although most plants have flowers with four whorls—protective leaves, petals, male parts, and female parts—and their typical sub-structures, they vary greatly between flowering plants.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This variation encompasses all aspects of flowers, including size, shape, and colour.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers range in size from Script error: No such module "convert". (duckweed) to Script error: No such module "convert". in diameter (corpse flower).Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Additionally, the four main parts of a flower are generally defined by their positions and not by their function. Many flowers lack some parts, have parts that are modified for other functions, or contain parts that look like what is typically another part.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In some flowers, organs such as stamens, stigmas, and sepals are modified to resemble petals. This is most common in cultivation (such as of roses), where flowers with many additional "petals" are found to be more attractive.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Most flowers have symmetry.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". When the flower is bisected through the central axis from any point and symmetrical halves are produced,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". the flower is said to be regular (as in sedges). This is an example of radial symmetry. If there is only one plane of symmetry (as in orchids),Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". the flower is said to be irregular. If, in very rare cases, they have no symmetry at all they are called asymmetric.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Floral symmetry is a key driver of diversity in flower morphology, because it is one of the main features derived through flower-plant coevolution. Irregular flowers often coevolve with specific pollinators, while radially symmetric flowers tend to attract a wider range of pollinators.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Template:Notetag
In the majority of species, individual flowers have both female parts and male parts — such flowers are described as being perfect, bisexual, or hermaphrodite. In some species of plants, the flowers are imperfect or unisexual: having only either male or female parts. If unisexual male and female flowers appear on the same plant, the species is called monoecious. However, if an individual plant is either female or male, the species is called dioecious.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Many flowers have nectaries, which are glands that produce nectar: a sugary fluid used to attract pollinators. Their shape varies between different plants,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". are they not considered as an organ on their own.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Some flowers are lacking or have only a highly reduced stalk, and so are attached directly to the plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". There are several structures, found in some plants, that resemble flowers or floral organs. These include: coronas, crown-like outgrowths;Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and pseudonectaries, that look like nectaries but do not contain nectar.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In plants where disease has taken hold, phyllody—leafy flower parts—may occur.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
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Hermaphrodite flowers have both sexes, monoecious plants have sexes on different flowers, and dioecious plants have either just female or just male flowers.
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Healthy (left) and infected (right) Hydrangea flower. Phytoplasma has caused the flower to develop leaves in place of petals.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Inflorescence
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In plants that have more than one flower on an axis, the collective cluster of flowers is called an inflorescence.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. These are known as pseudanthia.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". A single daisy or sunflower, for example, is not a flower but an inflorescence composed of numerous florets, or tiny flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". An inflorescence may include specialised stems and modified leaves known called bracts, as well as smaller bracteoles.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Floral diagrams and formulae
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A floral formula is a way to represent the structure of a flower using letters, numbers, and symbols in a compact way. It can represent both a group of species or a particular species, and usually gives ranges for the numbers of different organs. The format of floral formulae differs in different parts of the world, but the formulae all convey the same information.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Floral diagrams are schematic diagrams that can be used to show important features of flowers, including the relative positions of the various organs, the presence of organ fusion and symmetry, and structural details.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Colour
In contrast to the mostly green vegetative parts of plants, flowers are often colourful. This includes the petals and, in some plants, the stamens, anthers, stigmas, ovaries, pollen, styles, and even nectar.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". These colours are produced mainly by biological pigments, which are molecules that can absorb and retain energy from light.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Specific pigments, and so colours, provide different benefits to the plant. These benefits include protecting the plant against degradation and guiding pollinators—both general and specific—to the plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Colour, or colour effects, may also be produced by structural coloration, in which colour is produced by tiny surface structures interfering with waves of light.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This includes iridescence (as in some tulips) and photonic crystals (as in edelweiss), which diffract light using tiny grooves.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The colour of flowers can also change; sometimes this acts as a signal to pollinators (as in Viola cornuta). Change may also occur as a result of temperature; pH, as in the anthoxanthins found in Hydrangea; metals; sugars; and cell shape.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Development
Floral development begins with the transformation of vegetative growth into floral growth.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This is regulated by both genetic and environmental factors.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The eventual formation of a flower starts with a shoot apical meristem (SAM): a group of dividing cells responsible for leaves and buds. The organs which make up a flower—in most cases the sepals, petals, male parts, and female parts—grow out of a growth-limited floral meristem, which a SAM creates.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The ABC model of flower development can be used, for many plants, to describe how groups of genes come together to induce each organ being produced.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In general, all aspects of floral development are controlled by a gene regulatory network of specialised MADS-box genes—which includes the ABC genes—and associated proteins.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". For plants, the transition into flowering is a major change and must occur at the right time so as to ensure reproductive success. Plants determine this time by interpreting both internal and environmental cues, such as day length.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
The ABC model was the first unifying principle in the development of flowers, and its major tenets have been found to hold in most flowering plants.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". It describes how three groups of genes—A, B, and C—are responsible for the development of flowers. These three gene groups' activities interact together to determine the developmental identities of the primordia organ within the floral apical meristem. Alone, A genes produce sepals in the first whorl. Together, A and B produce the petals in the second whorl. C genes alone produce carpels in the centre of the flower. C and B together produce the stamens in the third whorl.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This can also be extended to the more complex ABCDE model, which adds an additional two gene groups to explain the development of structures like ovules.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
The transition to flowering is one of the major phase changes that a plant makes during its life cycle.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The transition must take place at a time that is favourable for fertilisation and the formation of seeds, hence ensuring maximal reproductive success. To meet these needs a plant can interpret important internal and environmental cues such as: changes in levels of plant hormones (such as gibberellins),Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". seasonable temperature, and day length changes.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Many plants, including many of those that have more than two-year lifespans and just two-year lifespans, require cold exposure to flower.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". These cues are interpreted molecularly through a complex signal called florigen, which involves a variety of genes. Florigen is produced in the leaves in reproductively favourable conditions and acts in stem tips to force switching from developing leaves to flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Once developed, flowers may selectively open and close their flowers at different times of day; usually around dusk and dawn.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". They may also track the path of the sun to remain warm—potentially both for their own benefit and to attract pollinators. Both of these mechanisms are controlled by a plant's circadian rhythm and in response to environmental changes.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
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Diagram showing the floral organs within a developing rose flower, or rose bud
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Diagram of the ABC model of development
Pollination
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Since the flowers are the reproductive organs of the plant, they mediate the joining of the sperm, contained within pollen, to the eggs in the ovules—contained in the ovary.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Pollination is this movement of pollen from the male parts to the female parts.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". It occurs either between flowers (or from one part of a flower to another) of the same plant, as in self-pollination, or between flowers of different plants, as in cross-pollination. Cross-pollination is more common in flowering plants as it increases genetic variation.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Pollination typically only takes place when the flower is fully expanded and functional.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Flowering plants usually face evolutionary pressure to optimise the transfer of their pollen, and this is typically reflected in the morphology of their flowers and their reproductive strategies.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Agents that transport pollen between plants are called vectors. Around 80% of flowering plants make use of biotic or living vectors. Others use abiotic or non-living vectors, or some combination of the two.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Biotic pollination
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Flowers that use biotic vectors attract and use animals to transfer pollen from one flower to the next. Often they are shaped and designed to both attract pollinators and ensure pollen is transferred effectively.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers most commonly employ insects,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". but also: birds, bats, lizards,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". other mammals,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". snails and slugs,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and, in rare cases, crustaceans and worms.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Rewards given to pollinators by flowers to encourage pollination include: food (such as pollen, starch, or nectar), mates, shelter, a place to raise their young, and pseudocopulation (sexual deception).Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In the latter, the flower is scented or shaped so as to encourage sexual arousal and pollination from the subsequent intercourse.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". They may also be attracted by various stimuli such as size and scent (as in carrion flowers). Colour is also a factor, and includes nectar guides, which show pollinators where to look for nectar; they may be visible only under ultraviolet light.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Many flowers have close relationships with just one or a few specific pollinators. They may be structured to allow or encourage pollination from these organisms. This increases efficiency, because there is a higher chance pollination comes from pollen of the same species of plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This close relationship is an example of coevolution, as the plant and pollinator have developed together over a long period to match each other's needs.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Abiotic pollination
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Flowers that use abiotic, or non-living, vectors use the wind or, much less commonly, water, to move pollen from one flower to the next.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Wind-dispersed species do not need to attract pollinators and therefore tend not to grow large, showy, or colourful flowers, and do not have nectaries, nor a noticeable scent.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Whereas the pollen of insect-pollinated flowers is usually large, sticky, and rich in protein to act as a "reward", wind-pollinated flowers' pollen is typically small, very light, smooth, and of little nutritional value.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Script error: No such module "string".
Fertilisation and seed development
Fertilisation is the fusion of the male and female sex cells to produce a zygote, from which a new organism develops.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In humans, sexual intercourse results in the depositing of sperm cells into the vagina. Although not all survive, they travel until one reaches the egg in the fallopian tube, where the male and female sex cells fuse in the process of fertilisation.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
In flowering plants, fertilisation is preceded by pollination, which is the movement of pollen from the stamen to the carpel. It encompasses both plasmogamy, the fusion of the protoplasts (cell without cell wall), and karyogamy, the fusion of the nuclei. When pollen lands on the stigma of the flower it begins creating a pollen tube, which runs down through the style and into the ovary. After penetrating the centre-most part of the ovary it enters the egg apparatus and is guided by a specialised cell.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Next, the end of the pollen tube bursts and releases the two sperm cells, one of which makes its way to an egg, while also losing its cell membrane and much of the jelly-like substance that fills its cells. The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote; a diploid cell, containing two copies of each chromosome.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowering plants undergo double fertilisation, which involves both karyogamy and plasmogamy. In double fertilisation the second sperm cell subsequently also fuses with the two polar nuclei of the central cell. Since all three nuclei are haploid, they result in a large nutrient tissue nucleus which is triploid.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Seed and fruit development
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Following its formation, the zygote begins to grow through nuclear and cellular divisions, called mitosis, eventually becoming a small group of cells. One section of it becomes the embryo,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". while the other becomes the suspensor; a structure which forces the embryo into the endosperm and is later undetectable. Two small groups of cells also form at this time, which later become the cotyledon, or initial leaf, which is used as an energy store. The next stage involves the growth of several key structures, including: the embryotic root, the embryotic stem, and the root or shoot junction itself. In the final step, vascular tissue develops around the seed.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
The ovary, inside which the seed is forming from the ovule, grows into a fruit. All the other main floral parts wither and die during this development, including: the style, stigma, stamens, petals, and sepals. This process is called floral senescence; it is often accelerated or initiated by the completion of pollination. Death is preferred because flowers are costly to the plant; nevertheless, flowers can last for between a few hours and several months.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The fruit contains three main structures: the outer layer of peel; the fleshy part; and the stone, or innermost layer. The pericarp, which may include one or more of these structures, represents collectively the fruit wall—everything but the seed. The size, shape, toughness, and thickness of the pericarp varies among different dry and fleshy fruits. These traits are directly connected to the plant's method of seed dispersal, since the purpose of fruit is to encourage or enable the seed's dispersal and protect the seed while doing so.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Seed dispersal
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Following the pollination of a flower, fertilisation, and finally the development of a seed and fruit, a mechanism, or vector, is typically used to disperse the fruit away from the plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In flowering plants, seeds are dispersed away from the plant so as to not force competition between the mother and daughter plants,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". as well as to enable the colonisation of new areas. Vectors can generally be divided into two categories: external vectors and internal vectors.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". External vectors include living things like birds or bats, or non-living things such as water and wind.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Internal vectors, which are derived from the plant itself,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". include, for example, the fruit exploding to release the seeds, as in dwarf mistletoes.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Evolution
Flowers originated between 150 and 190 million years ago, during the Jurassic.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Although molecular analyses indicate this early appearance of angiosperms—flowering plants, the earliest definitive evidence from the fossil record comes from between 125 and 130 million years ago, during the Early Cretaceous.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Template:Notetag The exact time at which angiosperms diverged from other seed plants is a classic open question in evolutionary biology.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Prior to the advent of flowers, plants reproduced using cones (as in gymnosperms),Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and spores (as in pteridophytes).Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The transformation of spore-producing leaves into structures like stamens and carpels, is the most clear milestone in the complex evolution of flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". There is debate both over whether these and other changes happened gradually or as sudden shifts like homeotic mutations, and which aspect of flower morphology came first.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
The flower was the angiosperms' most significant evolutionary innovation,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". granting the ability to effectively take advantage of animal pollinators.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Other evolutionary advantages included: being able to have both male and female parts on the same axis; and on this axis have carpels, to protect the ovules; stamens, to present the pollen; and the perianth, to provide protection. In addition, they pioneered double fertilisation, which allows energy investment (into endosperm) to be prolonged until after pollination. The gametophytes, which lead to sex cells, were very reduced, which allowed for greater protection of this critical process.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". The net effect of these features was greater reproductive security and efficiency.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This allowed the angiosperms to replace many other seed plants—such as Pinales, cycads, Gnetophyta and Ginkgoales—in the majority of ecosystems.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
A key driving force in the evolution of flowers is coevolution, where pollinator and flower evolve with one another,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". often to their mutual benefit. This is particularly prominent in insect species such as bees, but is also found in flower-pollinator relationships with birds and bats. Many flowers have evolved in such a way so as to make pollination by specific species easier, thus providing greater efficiency and also ensuring higher rates of pollination. This is because they receive less pollen from other plant species.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". However, this close interdependence increases the risk of extinction, since the extinction of either member almost certainly means the extinction of the other member as well.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Modern-day flowers exhibit a variety of features derived through coevolution including: shape, size, symmetry, timing of flower opening, colour, scent, and pollinator rewards (including pollen, nectar, and oils).Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". For example, Japanese honeysuckle flowers strategically open during the night to attract nocturnal moths, which are more efficient pollinators than diurnal bees.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". With the innovation of the flower—and other adaptations—angiosperms rapidly diversified.Template:Notetag Approximately 90% of all living land plant species are angiosperms.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". This is attributed, in part, to coevolution, which caused specialisation and so speciation; where populations diverge into separate species.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Both the strength of close pollinator-flower relationships and the survival of either species are effected by climate change. Reducing numbers of pollinators have led to the extinction of many flowering plants.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Taxonomy
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In plant taxonomy, which is the study of plant classification and identification, the morphology of plants' flowers is used extensively—and has been since at least classical Greece.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Despite earlier works, Carl Linnaeus's 1753 book Species Plantarum, in which he laid out his system of classification, is regarded as the first taxonomic work to recognise the significance of flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". He identified 24 classes of flowering plants, based mainly on the number, length, and union of the stamens.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Subsequent systems in the 18th and 19th centuries focused more on natural characteristics. This included taking into account the rest of the plant, so that diverse plants weren't put into the same groups, as often happened in Linnaeus's system.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
In 1963, the biologists Robert Sokal and Peter Sneath created the method of numerical taxonomy, which differentiates taxa based on their tabulated morphological characteristics; such as their flowers. This was an effort to make plant taxonomy more objective, but it remained inconsiderate of evolution, and so not useful in that context.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". While this and earlier methods, such as Linnaeus's, used morphological features, many botanists today employ genetic sequencing, the study of cells, and the study of pollen. These come as a result of advancements in DNA-related science.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Despite this, morphological characteristics such as the nature of the flower and inflorescence still make up the bedrock of plant taxonomy.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Uses
Over millennia, humans have come to use flowers for a variety of purposes around the world, including decoration, medicine, drugs,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". food, spices,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". perfumes,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and essential oils. Many flowers are edible and are often used in drinks and dishes, such as salads, for taste, scent, and decoration.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Inflorescences and the bracts or stems of some flowers are commonly described as vegetables. These include: broccoli, cauliflower, and artichoke. Flowers may be eaten freshly after being picked, or dried and eaten later.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Floristry is the production and sale of flowers, and involves preparing freshly cut flowers and arranging them—in a bouquet, for example—to the client's liking.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Most crop plants have flowers,Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". and they produce much of the most common crop products—such as seeds and fruits;Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". around half of all cropland is used to grow three flowering plants: rice, wheat, and corn.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers are steeped to make teas, either alone, as in herbal teas, or in combination with the tea plant.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Essential oils and other flower extracts are widely used in herbal medicines and decoctions because they contain phytochemicals and may have anti-microbial effects.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers from many plants are also used in the production of drugs, such as cannabis, bush lily, and Madagascar periwinkle.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Some flowers are used in cooking as spices, these include saffron and cloves; derived from Crocus and Syzygium aromaticum respectively.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
In culture
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Flowers are the subject of much symbolism, and feature often in art, ritual, religious practices, and festivals. Plants have been cultivated in gardens for their flowers for around ten thousand years.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Flowers are associated with burial in many cultures, and are often placed by headstones to pay respect.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". They are also placed by statues or temples of religious or other figures—sometimes formed into floral wreaths.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In some places, the dead are buried covered in flowers or on a bed of flowers.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". They are also associated with love and celebration, and given to others in many places for this reason.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". Economic demand has led to the cultivation of flowers that are longer-lasting, more colourful, and visually appealing.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
Flowers feature extensively in art across a variety of mediums, and different flowers are ascribed symbolic meanings.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". For example, violets may represent modesty, virtue, or affection.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In addition to hidden meanings, flowers are used in flags, emblems, and seals. In this way, they represent countries or places. Some countries have national flowers; for example, Hibiscus × rosa-sinensis is the national flower of Malaysia.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters". In literature, flowers feature in imagery of places and as metaphors for pleasure, beauty, and life.Script error: No such module "Footnotes".Script error: No such module "Check for unknown parameters".
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Still life of flowers by Ambrosius Bosschaert, 1614
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A woman spreading flowers over a lingam
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Princess Désirée of Sweden carrying flowers at her wedding
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Flowers placed on a grave
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Floral photography
Notes
References
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Bibliography
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Further reading
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External links
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