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A flower, sometimes known as a bloom or
blossom In botany, blossoms are the flowers of stone fruit trees (genus ''Prunus'') and of some other plants with a similar appearance that flower profusely for a period of time in spring. Colloquially, flowers of orange are referred to as such as wel ...
, is the
reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
structure found in flowering plants (plants of the division
Angiospermae Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism for the union of
sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
with
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s. Flowers may facilitate outcrossing (fusion of sperm and eggs from different individuals in a population) resulting from cross-pollination or allow selfing (fusion of sperm and egg from the same flower) when self-pollination occurs. There are two types of pollination: self-pollination and cross-pollination. Self-pollination occurs when the
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
from the
anther The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
is deposited on the stigma of the same flower, or another flower on the same plant. Cross-pollination is when pollen is transferred from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination happens in flowers where the
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
and carpel mature at the same time, and are positioned so that the pollen can land on the flower's stigma. This pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators. Some flowers produce
diaspores In botany, a diaspore is a plant dispersal unit consisting of a seed or spore plus any additional tissues that assist dispersal. In some seed plants, the diaspore is a seed and fruit together, or a seed and elaiosome. In a few seed plants, the di ...
without fertilization (
parthenocarpy In botany and horticulture, parthenocarpy is the natural or artificially induced production of fruit without fertilisation of ovules, which makes the fruit seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds are ac ...
). Flowers contain sporangia and are the site where gametophytes develop. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer of
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
. After fertilization, the
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
of the flower develops into fruit containing seeds. In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to bring beauty to the environment, and also as objects of romance, ritual, esotericism, witchcraft, religion, holistic medicine, and as a source of
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...
.


Etymology

Flower is from the Middle English enm, flour, label=none, which referred to both the ground grain and the reproductive structure in plants, before splitting off in the 17th century. It comes originally from the Latin name of the Italian goddess of flowers, Flora. The early word for flower in English was ''blossom'', though it now refers to flowers only of fruit trees.


Morphology

The morphology of a flower, or its form and structure, can be considered in two parts: the vegetative part, consisting of non-reproductive structures such as
petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...
s; and the reproductive or sexual parts. A stereotypical flower is made up of four kinds of structures attached to the tip of a short stalk or axis, called a
receptacle Receptacle may refer to: Biology * Receptacle (botany), a plant anatomical part * Seminal receptacle, a sperm storage site in some insects Electrical engineering * Automobile auxiliary power outlet, formerly known as ''cigarette lighter recep ...
. Each of these parts or floral organs is arranged in a spiral called a
whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...
. The four main whorls (starting from the base of the flower or lowest node and working upwards) are the
calyx Calyx or calyce (plural "calyces"), from the Latin ''calix'' which itself comes from the Ancient Greek ''κάλυξ'' (''kálux'') meaning "husk" or "pod", may refer to: Biology * Calyx (anatomy), collective name for several cup-like structures ...
,
corolla Corolla may refer to: *Corolla (botany), the petals of a flower, considered as a unit *Toyota Corolla, an automobile model name * Corolla (headgear), an ancient headdress in the form of a circlet or crown * ''Corolla'' (gastropod), a genus of moll ...
,
androecium The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
, and gynoecium. Together the calyx and corolla make up the non-reproductive part of the flower called the perianth, and in some cases may not be differentiated. If this is the case, then they are described as tepals.


Perianth


Calyx

The sepals, collectively called the calyx, are modified
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
that occur on the outermost whorl of the flower. They are leaf-like, in that they have a broad base,
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta, stipules, and
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...
. Sepals are often waxy and tough, and grow quickly to protect the flower as it develops. They may be deciduous, but will more commonly grow on to assist in fruit dispersal. If the calyx is fused together it is called gamosepalous.


Corolla

The
petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...
s, together the corolla, are almost or completely fiberless 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 pollination. Although similar to leaves in shape, they are more comparable to stamens in that they form almost simultaneously with one another, but their subsequent growth is delayed. If the corolla is fused together it is called sympetalous.


Reproductive


Androecium

The
androecium The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
, or stamens, is the whorl of pollen producing male parts. Stamens consist typically of an anther, made up of four pollen sacs arranged in two thecae, connected to a filament, or stalk. The anther contains microsporocytes which become
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, the male gametophyte, after undergoing meiosis. Although they exhibit the widest variation among floral organs, the androecium is usually confined just to one whorl and to two whorls only in rare cases. Stamens range in number, size, shape, orientation, and in their point of connection to the flower.


Gynoecium

The gynoecium, or the carpels, is the female part of the flower found on the innermost whorl. Each carpel consists of a stigma, which receives pollen, a style, which acts as a stalk, and an
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
, which contains the ovules. Carpels may occur in one to several whorls, and when fused together are often described as a pistil. Inside the ovary, the ovules are suspended off of pieces of tissue called placenta.


Variation

Although this arrangement is considered "typical", plant species show a wide variation in floral structure. The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions or look like what is typically another part. In some families, like Ranunculaceae, the petals are greatly reduced and in many species the sepals are colorful and petal-like. Other flowers have modified stamens that are petal-like; the double flowers of
Peonie The peony or paeony is a flowering plant in the genus ''Paeonia'' , the only genus in the family Paeoniaceae . Peonies are native to Asia, Europe and Western North America. Scientists differ on the number of species that can be distinguished ...
s and Roses are mostly petaloid stamens. Many flowers have a
symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...
. When the perianth is bisected through the central axis from any point and symmetrical halves are produced, the flower is said to be actinomorphic or regular. This is an example of radial symmetry. When flowers are bisected and produce only one line that produces symmetrical halves, the flower is said to be irregular or zygomorphic. If, in rare cases, they have no symmetry at all they are called asymmetric. Flowers may be directly attached to the plant at their base ( sessile—the supporting stalk or stem is highly reduced or absent). The stem or stalk subtending a flower, or an inflorescence of flowers, is called a
peduncle Peduncle may refer to: *Peduncle (botany), a stalk supporting an inflorescence, which is the part of the shoot of seed plants where flowers are formed *Peduncle (anatomy), a stem, through which a mass of tissue is attached to a body **Peduncle (art ...
. If a peduncle supports more than one flower, the stems connecting each flower to the main axis are called
pedicels In botany, a pedicel is a stem that attaches a single flower to the inflorescence. Such inflorescences are described as ''pedicellate''. Description Pedicel refers to a structure connecting a single flower to its inflorescence. In the absenc ...
. The apex of a flowering stem forms a terminal swelling which is called the torus or receptacle. In the majority of species individual flowers have both
pistil Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...
s and stamens. These flowers are described by botanists as being perfect, bisexual, or
hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...
. 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 female or male the species is regarded as
dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
. However, where unisexual male and female flowers appear on the same plant, the species is called
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...
. Many flowers have nectaries, which are glands that produce a sugary fluid used to attract pollinators. They are not considered as an organ on their own.


Inflorescence

In those species that have more than one flower on an axis, the collective cluster of flowers is called an inflorescence. Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. The common example of this is most members of the very large composite ( Asteraceae) group. A single daisy or
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
, for example, is not a flower but a flower
head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...
—an inflorescence composed of numerous flowers (or florets). An inflorescence may include specialized stems and modified leaves known as
bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...
s.


Floral diagrams and formulae

A ''floral formula'' is a way to represent the structure of a flower using specific letters, numbers and symbols, presenting substantial information about the flower in a compact form. It can represent a taxon, usually giving ranges of the numbers of different organs, or particular species. Floral formulae have been developed in the early 19th century and their use has declined since. Prenner ''et al.'' (2010) devised an extension of the existing model to broaden the descriptive capability of the formula. The format of floral formulae differs in different parts of the world, yet they convey the same information. The structure of a flower can also be expressed by the means of
floral diagram Floral diagram is a graphic representation of flower structure. It shows the number of floral organs, their arrangement and fusion. Different parts of the flower are represented by their respective symbols. Floral diagrams are useful for flower i ...
s. The use of schematic diagrams can replace long descriptions or complicated drawings as a tool for understanding both floral structure and evolution. Such diagrams may show important features of flowers, including the relative positions of the various organs, including the presence of fusion and symmetry, as well as structural details.


Development

A flower develops on a modified shoot or ''axis'' from a determinate apical meristem (''determinate'' meaning the axis grows to a set size). It has compressed internodes, bearing structures that in classical plant morphology are interpreted as highly modified
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
. Detailed developmental studies, however, have shown that stamens are often initiated more or less like modified stems (caulomes) that in some cases may even resemble branchlets. Taking into account the whole diversity in the development of the androecium of flowering plants, we find a continuum between modified leaves (phyllomes), modified stems (caulomes), and modified branchlets (shoots).


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 is favorable for fertilization and the formation of
seeds A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm pl ...
, hence ensuring maximal
reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
success. To meet these needs a plant is able to interpret important endogenous and environmental cues such as changes in levels of
plant hormones Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...
and seasonable temperature and
photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
changes. Many perennial and most biennial plants require
vernalization Vernalization (from Latin ''vernus'', "of the spring") is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, ...
to flower. The molecular interpretation of these signals is through the transmission of a complex signal known as florigen, which involves a variety of genes, including Constans, Flowering Locus C and Flowering Locus T. Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes.The first step of the transition 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.


Organ development

The ABC model is a simple model that describes the genes responsible for the development of flowers. Three gene activities interact in a combinatorial manner to determine the developmental identities of the
primordia A primordium (; plural: primordia; synonym: anlage) in embryology, is an Organ (anatomy), organ or tissue in its earliest recognizable stage of development. Cell (biology), Cells of the primordium are called primordial cells. A primordium is the ...
organ within the floral apical meristem. These gene functions are called A, B, and C. A genes are expressed in only outer and lower most section of the apical meristem, which becomes a whorl 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 aberrant flowers and mutations in ''
Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...
'' and the snapdragon, ''
Antirrhinum majus ''Antirrhinum majus'', the common snapdragon (often - especially in horticulture - simply "snapdragon"), is a species of flowering plant belonging to the genus ''Antirrhinum''. The plant was placed in the family Plantaginaceae following a revis ...
''. For example, when there is a loss of B gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. 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.


Function

The principal purpose of a flower is the reproduction of the individual and the species. All flowering plants are '' heterosporous'', that is, every individual plant produces two types of
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
s. Microspores are produced by meiosis inside anthers and megaspores are produced inside ovules that are within an ovary. Anthers typically consist of four microsporangia and an ovule is an integumented megasporangium. Both types of spores develop into gametophytes inside sporangia. As with all heterosporous plants, the gametophytes also develop inside the spores, i. e., they are endosporic. In the majority of plant species, individual flowers have both functional carpels and stamens. Botanists describe these flowers as perfect or bisexual, and the species as hermaphroditic. In a minority of plant species, their flowers lack one or the other reproductive organ and are described as imperfect or unisexual. If the individual plants of a species each have unisexual flowers of both sexes then the species is
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...
. Alternatively, if each individual plant has only unisexual flowers of the same sex then the species is
dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...
.


Pollination

The primary purpose of the flower is
reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...
. Since the flowers are the reproductive organs of the plant, they mediate the joining of the sperm, contained within pollen, to the ovules — contained in the ovary. Pollination is the movement of pollen from the anthers to the stigma. Normally pollen is moved from one plant to another, known as cross-pollination, but many plants are able to self-pollinate. Cross-pollination is preferred because it allows for
genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, ...
, which contributes to the survival of the species. Many flowers are dependent, then, upon external factors for pollination, such as: the wind, water, animals, and especially insects. Larger animals such as birds, bats, and even some
pygmy possum The pygmy possums are a family of small possums that together form the marsupial family Burramyidae. The five extant species of pygmy possum are grouped into two genera. Four of the species are endemic to Australia, with one species also co-occu ...
s, however, can also be employed. To accomplish this, flowers have specific designs which encourage the transfer of pollen from one plant to another of the same species. The period of time during which this process can take place (when the flower is fully expanded and functional) is called ''
anthesis Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period. The onset of anthesis is spectacular in some species. In ''Banksia'' species, for example, anthesis involves the extension ...
'', hence the study of pollination biology is called ''
anthecology Anthecology, or pollination biology, is the study of pollination as well as the relationships between flowers and their pollinators. Floral biology is a bigger field that includes these studies. Most flowering plants, or angiosperms, are pollinat ...
''. Flowering plants usually face evolutionary pressure to optimize the transfer of their
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, and this is typically reflected in the morphology of the flowers and the behaviour of the plants. Pollen may be transferred between plants via a number of 'vectors,' or methods. Around 80% of flowering plants make use of biotic, or living vectors. Others use abiotic, or non-living, vectors and some plants make use of multiple vectors, but most are highly specialised. Though some fit between or outside of these groups, most flowers can be divided between the following two broad groups of pollination methods:


Biotic pollination

Flowers that use biotic vectors attract and use insects, bats, birds, or other animals to transfer pollen from one flower to the next. Often they are specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or a mate). 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 flowers rely on simple proximity between flower parts to ensure pollination, while others have elaborate designs to ensure pollination and prevent self-pollination. Flowers use animals including: insects ('' entomophily''), birds ('' ornithophily''), bats ('' chiropterophily''), lizards, and even snails and slugs (''malacophilae'').


Attraction methods

Plants cannot move from one location to another, thus many flowers have evolved to attract animals to transfer pollen between individuals in dispersed populations. Most commonly, flowers are insect-pollinated, known as '' entomophilous''; literally "insect-loving" in Greek. To attract these insects flowers commonly have glands called ''nectaries'' on various parts that attract animals looking for nutritious
nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...
. Birds and bees have
color vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...
, enabling them to seek out "colorful" flowers. Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar; they may be visible only under ultraviolet light, which is visible to bees and some other insects. Flowers also attract pollinators by scent, though not all flower scents are appealing to humans; a number of flowers are pollinated by insects that are attracted to rotten flesh and have flowers that smell like dead animals. These are often called Carrion flowers, including plants in the genus '' Rafflesia'', and the titan arum. Flowers pollinated by night visitors, including bats and moths, are likely to concentrate on scent to attract pollinators and so most such flowers are white. Flowers are also specialized in shape and have an arrangement of the
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
s that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant. Other flowers use mimicry or pseudocopulation to attract pollinators. Many orchids for example, produce flowers resembling female bees or wasps in colour, shape, and scent. Males move from one flower to the next in search of a mate, pollinating the flowers.


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 an example of
coevolution In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...
, as the flower and pollinator have developed together over a long period of time to match each other's needs. This close relationship compounds the negative effects of extinction, however, since the extinction of either member in such a relationship would almost certainly mean the extinction of the other member as well.


Abiotic pollination

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. In wind-dispersed ( anemophilous) species, the tiny pollen grains are carried, sometimes many thousands of kilometres, by the wind to other flowers. Common examples include the grasses,
birch trees A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech-oak family Fagaceae. The genus ''Betula'' contains 3 ...
, along with many other species in the order '' fagales'', ragweeds, and many sedges. They have no need to attract pollinators and therefore tend not to grow large, showy, or colorful flowers, and do not have nectaries, nor a noticeable scent. Because of this, plants typically have many thousands of tiny flowers which have comparatively large, feathery stigmas; to increase the chance of pollen being received. Whereas the pollen of entomophilous flowers is usually large, sticky, and rich in protein (to act as a "reward" for pollinators), anemophilous flower pollen is typically small-grained, very light, smooth, and of little nutritional value to insects. In order for the wind to effectively pick up and transport the pollen, the flowers typically have anthers loosely attached to the end of long thin filaments, or pollen forms around a
catkin A catkin or ament is a slim, cylindrical flower cluster (a spike), with inconspicuous or no petals, usually wind-pollinated (anemophilous) but sometimes insect-pollinated (as in ''Salix''). They contain many, usually unisexual flowers, arranged cl ...
which moves in the wind. Rarer forms of this involve individual flowers being moveable by the wind (
Pendulous This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...
), or even less commonly; the anthers exploding to release the pollen into the wind. Pollination through water ( hydrophily) is a much rarer method, occurring in only around 2% of abiotically pollinated flowers. Common examples of this include ''Calitriche autumnalis'', '' Vallisneria spiralis'' and some sea-grasses. One characteristic which most species in this group share is a lack of an
exine Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, or protective layer, around the pollen grain. Paul Knuth identified two types of hydrophilous pollination in 1906 and Ernst Schwarzenbach added a third in 1944. Knuth named his two groups ''Hyphydrogamy'' and the more common ''Ephydrogamy.'' In ''Hyphydrogamy'' pollination occurs below the surface of the water and so the pollen grains are typically negatively buoyant. For marine plants that exhibit this method the stigmas are usually stiff, while freshwater species have small and feathery stigmas. In ''Ephydrogamy'' pollination occurs on the surface of the water and so the pollen has a low density to enable floating, though many also use rafts, and are hydrophobic. Marine flowers have floating thread-like stigmas and may have adaptations for the tide, while freshwater species create indentations in the water. The third category, set out by Schwarzenbach, is those flowers which transport pollen above the water through conveyance. This ranges from floating plants, ('' Lemnoideae''), to staminate flowers ('' Vallisneria''). Most species in this group have dry, spherical pollen which sometimes forms into larger masses, and female flowers which form depressions in the water; the method of transport varies.


Mechanisms

Flowers can be pollinated by two mechanisms; cross-pollination and self-pollination. No mechanism is indisputably better than the other as they each have their advantages and disadvantages. Plants use one or both of these mechanisms depending on their habitat and ecological niche.


Cross-pollination

Cross-pollination is the pollination of the carpel by pollen from a different plant of the same species. Because the genetic make-up of the sperm contained within the pollen from the other plant is different, their combination will result in a new, genetically distinct, plant, through the process of sexual reproduction. Since each new plant is genetically distinct, the different plants show
variation Variation or Variations may refer to: Science and mathematics * Variation (astronomy), any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon * Genetic variation, the difference in DNA among individual ...
in their physiological and structural adaptations and so the population as a whole is better prepared for an adverse occurrence in the environment. Cross-pollination, therefore, increases the survival of the species and is usually preferred by flowers for this reason.


Self-pollination

Self-pollination is the pollination of the carpel of a flower by pollen from either the same flower or another flower on the same plant, leading to the creation of a genetic clone through
asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
. This increases the reliability of producing seeds, the rate at which they can be produced, and lowers the amount energy needed. But, most importantly, it limits
genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, ...
. In addition, self-pollination causes inbreeding depression, due largely to the expression of recessive deleterious mutations. The extreme case of self-fertilization, when the ovule is fertilized by pollen from the same flower or plant, occurs in flowers that always self-fertilize, such as many dandelions. Some flowers are self-pollinated and have flowers that never open or are self-pollinated before the flowers open; these flowers are called cleistogamous; many species in the genus ''Viola'' exhibit this, for example. Conversely, many species of plants have ways of preventing self-pollination and hence, 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-incompatible. In ''
Clianthus puniceus ''Clianthus puniceus'', common name kaka beak (''Kōwhai Ngutu-kākā'' in Māori language, Māori), is a species of flowering plant in the genus ''Clianthus'' of the legume family (biology), family Fabaceae, native plant, native to New Zealand' ...
'', (pictured), self-pollination is used strategically as an "insurance policy." When a pollinator, in this case a bird, visits ''C. puniceus'' it rubs off the stigmatic covering and allows for pollen from the bird to enter the stigma. If no pollinators visit, however, then the stigmatic covering falls off naturally to allow for the flower's own anthers to pollinate the flower through self-pollination.


Allergies

Pollen is a large contributor to asthma and other respiratory allergies which combined affect between 10 and 50% of people worldwide. This number appears to be growing, as the temperature increases due to climate change mean that plants are producing more pollen, which is also more allergenic. Pollen is difficult to avoid, however, because of its small size and prevalence in the natural environment. Most of the pollen which causes allergies is that produced by wind-dispersed pollinators such as the grasses,
birch trees A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech-oak family Fagaceae. The genus ''Betula'' contains 3 ...
, oak trees, and ragweeds; the allergens in pollen are proteins which are thought to be necessary in the process of pollination.


Fertilization

Fertilization, also called ''Synagmy,'' occurs following pollination, which is the movement of pollen from the stamen to the carpel. It encompasses both plasmogamy, the fusion of the
protoplast Protoplast (), is a biological term coined by Hanstein in 1880 to refer to the entire cell, excluding the cell wall. Protoplasts can be generated by stripping the cell wall from plant, bacterial, or fungal cells by mechanical, chemical or enzy ...
s, and
karyogamy Karyogamy is the final step in the process of fusing together two haploid eukaryotic cells, and refers specifically to the fusion of the two nuclei. Before karyogamy, each haploid cell has one complete copy of the organism's genome. In order for ...
, the fusion of the nuclei. When pollen lands on the stigma of the flower it begins creating a
pollen tube A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells fro ...
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 into one
synergid In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...
. At this point 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 its
protoplasm Protoplasm (; ) is the living part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acid, and macromolecules such as proteins, polysaccharides, lipids, etc. In some defini ...
. The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote, a
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
(two copies of each chromosome) cell. Whereas in fertilization only plasmogamy, or the fusion of the whole sex cells, results, in Angiosperms (flowering plants) a process known as double fertilization, which involves both karyogamy and plasmogamy, occurs. In double fertilization the second sperm cell subsequently also enters the synergid and fuses with the two polar nuclei of the central cell. Since all three nuclei are
haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
, they result in a large
endosperm The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the embryo and ...
nucleus which is triploid.


Seed development

Following the formation of zygote it begins to grow through nuclear and cellular divisions, called
mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
, eventually becoming a small group of cells. One section of it becomes the
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
, while the other becomes the suspensor; a structure which forces the embryo into the
endosperm The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the embryo and ...
and is later undetectable. Two small
primordia A primordium (; plural: primordia; synonym: anlage) in embryology, is an Organ (anatomy), organ or tissue in its earliest recognizable stage of development. Cell (biology), Cells of the primordium are called primordial cells. A primordium is the ...
also form at this time, that later become the cotyledon, which is used as an energy store. Plants which grow out one of these primordia are called monocotyledons, while those that grow out two are
dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, t ...
s. The next stage is called the Torpedo stage and involves the growth of several key structures, including: the radicle (embryotic root), the epicotyl (embryotic stem), and the hypocotyl, (the root/shoot junction). In the final step vascular tissue develops around the seed.


Fruit development

The ovary, inside which the seed is forming from the ovule, grows into a fruit. All the other main floral parts die during this development, including: the style, stigma, sepals, stamens, and petals. The fruit contains three structures: the exocarp, or outer layer, the mesocarp, or the fleshy part, and the endocarp, or innermost layer, while the fruit wall is called the pericarp. The size, shape, toughness, and thickness varies among different fruit. This is because it is directly connected to the method of seed dispersal; that being the purpose of fruit - to encourage or enable the seed's dispersal and protect the seed while doing so.


Seed dispersal

Following the pollination of a flower, fertilization, and finally the development of a seed and fruit, a mechanism is typically used to disperse the fruit away from the plant. In Angiosperms (flowering plants) seeds are dispersed away from the plant so as to not force competition between the mother and the daughter plants, as well as to enable the colonisation of new areas. They are often divided into two categories, though many plants fall in between or in one or more of these:


Allochory

In allochory, plants use an external vector, or carrier, to transport their seeds away from them. These can be either
biotic Biotics describe living or once living components of a community; for example organisms, such as animals and plants. Biotic may refer to: *Life, the condition of living organisms *Biology, the study of life * Biotic material, which is derived from ...
(living), such as by birds and ants, or abiotic (non-living), such as by the wind or water.''''


Biotic vectors

Many plants use biotic vectors to disperse their seeds away from them. This method falls under the umbrella term ''Zoochory,'' while ''
Endozoochory In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
,'' also known as ''fruigivory,'' refers specifically to plants adapted to grow fruit in order to attract animals to eat them. Once eaten they go through typically go through animal's digestive system and are dispersed away from the plant. Some seeds are specially adapted either to last in the gizzard of animals or even to germinate better after passing through them. They can be eaten by birds (''ornithochory)'', bats (''chiropterochory)'', rodents, primates, ants (''
myrmecochory Myrmecochory ( (sometimes myrmechory); from grc, μύρμηξ, mýrmēks ("ant") and ''khoreíā'' ("circular dance") is seed dispersal by ants, an ecologically significant ant–plant interaction with worldwide distribution. Most myrmeco ...
''), non-bird sauropsids (''saurochory)'', mammals in general ''(mammaliochory)'', and even fish. Typically their fruit are fleshy, have a high nutritional value, and may have chemical attractants as an additional "reward" for dispersers. This is reflected morphologically in the presence of more pulp, an
aril An aril (pronounced ), also called an arillus, is a specialized outgrowth from a seed that partly or completely covers the seed. An arillode or false aril is sometimes distinguished: whereas an aril grows from the attachment point of the see ...
, and sometimes an
elaiosome Elaiosomes ( grc, ἔλαιον ''élaion'' "oil" + ''sóma'' "body") are fleshy structures that are attached to the seeds of many plant species. The elaiosome is rich in lipids and proteins, and may be variously shaped. Many plants have elaio ...
(primarily for ants), which are other fleshy structures.'''' ''
Epizoochory In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
'' occurs in plants whose seeds are adapted to cling on to animals and be dispersed that way, such as many species in the genus '' Acaena.'' Typically these plants seed's have hooks or a viscous surface to easier grip to animals, which include birds and animals with fur. Some plants use
mimesis Mimesis (; grc, μίμησις, ''mīmēsis'') is a term used in literary criticism and philosophy that carries a wide range of meanings, including ''imitatio'', imitation, nonsensuous similarity, receptivity, representation, mimicry, the act ...
, or imitation, to trick animals into dispersing the seeds and these often have specially adapted colors.'''' The final type of ''Zoochory'' is called '' Synzoochory,'' which involves neither the digestion of the seeds, nor the unintentional carrying of the seed on the body, but the deliberate carrying of the seeds by the animals. This is usually in the mouth or beak of the animal (called ''Stomatochory''), which is what is used for many birds and all ants.


Abiotic vectors

In abiotic dispersal plants use the vectors of the wind, water, or a mechanism of their own to transport their seeds away from them.'''' '' Anemochory'' involves using the wind as a vector to disperse plant's seeds. Because these seeds have to travel in the wind they are almost always small - sometimes even dust-like, have a high surface-area-to-volume ratio, and are produced in a large number - sometimes up to a million. Plants such as tumbleweeds detach the entire shoot to let the seeds roll away with the wind. Another common adaptation are wings, plumes or balloon like structures that let the seeds stay in the air for longer and hence travel farther. In ''
Hydrochory In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
'' plants are adapted to disperse their seeds through bodies of water and so typically are buoyant and have a low
relative density Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...
with regards to the water. Commonly seeds are adapted morphologically with hydrophobic surfaces, small size, hairs, slime, oil, and sometimes air spaces within the seeds.'''' These plants fall into three categories: ones where seeds are dispersed on the surface of water currents, under the surface of water currents, and by rain landing on a plant.


Autochory

In
autochory In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
, plants create their own vectors to transport the seeds away from them. Adaptations for this usually involve the fruits exploding and forcing the seeds away
ballistically Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing an ...
, such as in '' Hura crepitans,'' or sometimes in the creation of creeping
diaspores In botany, a diaspore is a plant dispersal unit consisting of a seed or spore plus any additional tissues that assist dispersal. In some seed plants, the diaspore is a seed and fruit together, or a seed and elaiosome. In a few seed plants, the di ...
.'''' Because of the relatively small distances that these methods can disperse their seeds, they are often paired with an external vector.''''


Evolution

While land plants have existed for about 425 million years, the first ones reproduced by a simple adaptation of their aquatic counterparts:
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
s. In the sea, plants—and some animals—can simply scatter out genetic clones of themselves to float away and grow elsewhere. This is how early plants reproduced. But plants soon evolved methods of protecting these copies to deal with drying out and other damage which is even more likely on land than in the sea. The protection became the seed, though it had not yet evolved the flower. Early seed-bearing plants include the ginkgo and
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s. Several groups of extinct gymnosperms, particularly seed ferns, have been proposed as the ancestors of flowering plants but there is no continuous fossil evidence showing exactly how flowers evolved. The apparently sudden appearance of relatively modern flowers in the fossil record posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. Recently discovered angiosperm fossils such as ''Archaefructus'', along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. An early fossil of a flowering plant, '' Archaefructus liaoningensis'' from China, is dated about 125 million years old. Even earlier from China is the 125–130 million years old '' Archaefructus sinensis''. In 2015 a plant (130 million-year-old '' Montsechia vidalii'', discovered in Spain) was claimed to be 130 million years old. In 2018, scientists reported that the earliest flowers began about 180 million years ago. Recent DNA analysis ( molecular systematics) shows that ''Amborella trichopoda'', found on the Pacific island of New Caledonia, is the only species in the
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
to the rest of the flowering plants, and morphological studies suggest that it has features which may have been characteristic of the earliest flowering plants. Besides the hard proof of flowers in or shortly before the Cretaceous, there is some circumstantial evidence of flowers as much as 250 million years ago. A chemical used by plants to defend their flowers, oleanane, has been detected in fossil plants that old, including
gigantopterid Gigantopterids (Gigantopteridales) is an extinct, possibly polyphyletic group of plants known from the Permian period. Gigantopterids were among the most advanced land plants of the Paleozoic Era and disappeared around the Permian–Triassic exti ...
s, 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 Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...
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 Bisexuality is a romantic or sexual attraction or behavior toward both males and females, or to more than one gender. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, whi ...
(in plants, this means both male and female parts on the same flower), and to be dominated by the
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
(female part). As flowers grew more advanced, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant, or at least "ovary inferior". The general assumption is that the function of flowers, from the start, was to involve animals in the reproduction process. Pollen can be scattered without bright colors and obvious shapes, which would therefore be a liability, using the plant's resources, unless they provide some other benefit. One proposed reason for the sudden, fully developed appearance of flowers is that they evolved in an isolated setting like an island, or chain of islands, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example), the way many island species develop today. This symbiotic relationship, with a hypothetical wasp bearing pollen from one plant to another much the way fig wasps do today, could have eventually resulted in both the plant(s) and their partners developing a high degree of specialization. Island genetics is believed to be a common source of
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
, especially when it comes to radical adaptations which seem to have required inferior transitional forms. Note that the wasp example is not incidental; bees, apparently evolved specifically for symbiotic plant relationships, are descended from wasps. Likewise, most fruit used in plant reproduction comes from the enlargement of parts of the flower. This fruit is frequently a tool which depends upon animals wishing to eat it, and thus scattering the seeds it contains. While many such symbiotic relationships remain too fragile to survive competition with mainland organisms, flowers proved to be an unusually effective means of production, spreading (whatever their actual origin) to become the dominant form of land plant life. Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that many of them cannot be pollinated in nature. Many modern, domesticated flowers used to be simple weeds, which only sprouted when the ground was disturbed. Some of them tended to grow with human crops, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.


Colour

Many flowering plants reflect as much light as possible within the range of visible wavelengths of the pollinator the plant intends to attract. Flowers that reflect the full range of visible light are generally perceived as '' white'' by a human observer. An important feature of white flowers is that they reflect equally across the visible spectrum. While many flowering plants use white to attract pollinators, the use of color is also widespread (even within the same species). Color allows a flowering plant to be more specific about the pollinator it seeks to attract. The color model used by human color reproduction technology ( CMYK) relies on the modulation of pigments that divide the spectrum into broad areas of absorption. Flowering plants by contrast are able to shift the transition point wavelength between absorption and reflection. If it is assumed that the visual systems of most pollinators view the visible spectrum as circular then it may be said that flowering plants produce color by absorbing the light in one region of the spectrum and reflecting the light in the other region. With CMYK, color is produced as a function of the amplitude of the broad regions of absorption. Flowering plants by contrast produce color by modifying the frequency (or rather wavelength) of the light reflected. Most flowers absorb light in the blue to yellow region of the spectrum and reflect light from the green to red region of the spectrum. For many species of flowering plant, it is the transition point that characterizes the color that they produce. Color may be modulated by shifting the transition point between absorption and reflection and in this way a flowering plant may specify which pollinator it seeks to attract. Some flowering plants also have a limited ability to modulate areas of absorption. This is typically not as precise as control over wavelength. Humans observers will perceive this as degrees of saturation (the amount of ''white'' in the color).


Classical taxonomy

In plant taxonomy, which is the study of the classification and identification of plants, the morphology of plant's flowers are used extensively – and have been for thousands of years. Although the history of plant taxonomy extends back to at least around 300 B.C. with the writings of Theophrastus, the foundation of the modern science is based on works in the 18th and 19th centuries. Carl Linnaeus (1707–1778), was a Swedish botanist who spent most of his working life as a professor of natural history. His landmark 1757 book ''
Species Plantarum ' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genera. It is the first work to consistently apply binomial names and was the ...
'' lays out his system of classification as well as the concept of binomial nomenclature, the latter of which is still used around the world today. He identified 24 classes, based mainly on the number, length and union of the
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
s. The first ten classes follow the number of stamens directly (''Octandria'' have 8 stamens etc.), while class eleven has 11-20 stamens and classes twelve and thirteen have 20 stamens; differing only in their point of attachment. The next five classes deal with the length of the stamens and the final five with the nature of the reproductive capability of the plant; where the stamen grows; and if the flower is concealed or exists at all (such as in ferns). This method of classification, despite being artificial, was used extensively for the following seven decades, before being replaced by the system of another botanist.
Antoine Laurent de Jussieu Antoine Laurent de Jussieu (; 12 April 1748 – 17 September 1836) was a French botanist, notable as the first to publish a natural classification of flowering plants; much of his system remains in use today. His classification was based on an e ...
(1748–1836) was a French botanist whose 1787 work ''Genera plantarum: secundum ordines naturales disposita'' set out a new method for classifying plants; based instead on natural characteristics. Plants were divided by the number, if any, of cotyledons, and the location of the stamens. The next most major system of classification came in the late 19th century from the botanists Joseph Dalton Hooker (1817–1911) and George Bentham (1800–1884). They built on the earlier works of de Jussieu and Augustin Pyramus de Candolle and devised a system which is still used in many of the world's herbaria. Plants were divided at the highest level by the number of cotyledons and the nature of the flowers, before falling into orders ( families),
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
, and species. This system of classification was published in their '' Genera plantarum'' in three volumes between 1862 and 1883. It is the most highly regarded and deemed the "best system of classification," in some settings. Following the development in scientific thought after Darwin's '' On the Origin of Species'', many botanists have used more phylogenetic methods and the use of
genetic sequencing Genetic Sequencing may refer to: * DNA sequencing * Whole genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entiret ...
, cytology, and palynology has become increasingly common. Despite this, morphological characteristics such as the nature of the flower and inflorescence still make up the bedrock of plant taxonomy.


Symbolism

Many flowers have important
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
ic 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 United Kingdom, New Zealand, Australia and Canada,
red poppies ''Red Poppies'' () is a 1998 Chinese-language novel by the Tibetan Chinese writer Alai, whose theme is based on the Tibetan custom and traditions. The novel consists of 12 chapters with a total of 481,000 Chinese characters. It won the Mao Dun Li ...
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. Because of their varied and colorful appearance, flowers have long been a favorite subject of visual artists as well. Some of the most celebrated paintings from well-known painters are of flowers, such as Van Gogh's sunflowers series or Monet's water lilies. Flowers are also dried, freeze dried and pressed in order to create permanent, three-dimensional pieces of floral art. Flowers within art are also representative of the
female genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
, as seen in the works of artists such as Georgia O'Keeffe, Imogen Cunningham,
Veronica Ruiz de Velasco Veronica, Veronika, etc., may refer to: People * Veronica (name) * Saint Veronica * Saint Veronica of Syria Arts and media Comics and literature * ''Veronica'', an 1870 novel by Frances Eleanor Trollope * ''Veronica'', a 2005 novel by Mary Gaits ...
, and Judy Chicago, and in fact in Asian and western classical art. Many cultures around the world have a marked tendency to associate flowers with femininity. The great variety of delicate and beautiful flowers has inspired the works of numerous poets, especially from the 18th–19th century
Romantic Romantic may refer to: Genres and eras * The Romantic era, an artistic, literary, musical and intellectual movement of the 18th and 19th centuries ** Romantic music, of that era ** Romantic poetry, of that era ** Romanticism in science, of that e ...
era. Famous examples include William Wordsworth's ''
I Wandered Lonely as a Cloud "I Wandered Lonely as a Cloud" (also commonly known as "Daffodils") is a lyric poem by William Wordsworth. It is one of his most popular, and was inspired by a forest encounter on 15 April 1802 between he, his younger sister Dorothy and a "lon ...
'' and William Blake's ''
Ah! Sun-Flower "Ah! Sun-flower" is an illustrated poem written by the English poet, painter and printmaker William Blake. It was published as part of his collection ''Songs of Experience'' in 1794 (no.43 in the sequence of the combined book, ''Songs of Innocence ...
''. Their symbolism in dreams has also been discussed, with possible interpretations including "blossoming potential". The Roman goddess of flowers, gardens, and the season of Spring is Flora. The Greek goddess of spring, flowers and nature is
Chloris In Greek mythology, the name Chloris (; Greek Χλωρίς ''Chlōrís'', from χλωρός ''chlōrós'', meaning "greenish-yellow", "pale green", "pale", "pallid", or "fresh") appears in a variety of contexts. Some clearly refer to different char ...
. In
Hindu Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
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. Apart from the association with Vishnu, the Hindu tradition also considers the lotus to have spiritual significance. For example, it figures in the Hindu stories of creation.


Human use

History shows that flowers have been used by humans for thousands of years, to serve a variety of purposes. An early example of this is from about 4,500 years ago in Ancient Egypt, where flowers would be used to decorate women's hair. Flowers have also inspired art time and time again, such as in Monet's ''Water Lilies'' or William Wordsworth's poem about
daffodils ''Narcissus'' is a genus of predominantly spring flowering perennial plant, perennial plants of the amaryllis family, Amaryllidaceae. Various common names including daffodil,The word "daffodil" is also applied to related genera such as ''Ste ...
entitled: "
I Wandered Lonely as a Cloud "I Wandered Lonely as a Cloud" (also commonly known as "Daffodils") is a lyric poem by William Wordsworth. It is one of his most popular, and was inspired by a forest encounter on 15 April 1802 between he, his younger sister Dorothy and a "lon ...
". In modern times, people have sought ways to cultivate, buy, wear, or otherwise be around flowers and blooming plants, partly because of their agreeable appearance and
smell Smell may refer to; * Odor, airborne molecules perceived as a scent or aroma * Sense of smell, the scent also known scientifically as olfaction * "Smells" (''Bottom''), an episode of ''Bottom'' * The Smell, a music venue in Los Angeles, Californ ...
. Around the world, people use flowers to mark important events in their lives: * For new births or christenings * As a corsage or boutonniere worn at social functions or for holidays * As tokens of love or esteem * For wedding flowers for the bridal party, and for 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 A funeral is a ceremony connected with the final disposition of a corpse, such as a burial or cremation, with the attendant observances. Funerary customs comprise the complex of beliefs and practices used by a culture to remember and respect th ...
flowers and expressions of sympathy for the grieving * For worship. In Christianity,
chancel flowers Chancel flowers (also known as altar flowers) are flowers that are placed in the chancel of a Christian church. These chancel flowers are often paid for by members of a congregation as an offering of thanksgiving to God. Chancel flowers are often ...
often adorn churches. In
Hindu Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
culture, adherents commonly bring flowers as a gift to temples Flowers like
jasmine Jasmine ( taxonomic name: ''Jasminum''; , ) is a genus of shrubs and vines in the olive family (Oleaceae). It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are widely cultiva ...
have been used as a replacement for traditional tea in China for centuries. Most recently many other herbs and flowers used traditionally across the world are gaining importance to preapare a range of
floral tea A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...
. People therefore grow flowers around their homes, dedicate parts of their living space to flower gardens, pick wildflowers, or buy commercially-grown flowers from florists. Flowers provide less food than other major plant parts ( seeds, fruits, roots, stems and
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
), but still provide several important vegetables and spices. Flower vegetables include broccoli,
cauliflower Cauliflower is one of several vegetables in the species ''Brassica oleracea'' in the genus ''Brassica'', which is in the Brassicaceae (or mustard) family. It is an annual plant that reproduces by seed. Typically, only the head is eaten – the ...
and artichoke. The most expensive spice, saffron, consists of dried stigmas of a crocus. Other flower spices are
clove Cloves are the aromatic flower buds of a tree in the family Myrtaceae, ''Syzygium aromaticum'' (). They are native to the Maluku Islands (or Moluccas) in Indonesia, and are commonly used as a spice, flavoring or fragrance in consumer products, ...
s and capers.
Hops Hops are the flowers (also called seed cones or strobiles) of the hop plant ''Humulus lupulus'', a member of the Cannabaceae family of flowering plants. They are used primarily as a bittering, flavouring, and stability agent in beer, to whi ...
flowers are used to flavor beer. Marigold flowers are fed to chickens to give their egg yolks a golden yellow color, which consumers find more desirable; dried and ground marigold flowers are also used as a spice and colouring agent in Georgian cuisine. Flowers of the dandelion and
elder An elder is someone with a degree of seniority or authority. Elder or elders may refer to: Positions Administrative * Elder (administrative title), a position of authority Cultural * North American Indigenous elder, a person who has and tr ...
are often made into wine. Bee
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, pollen collected from bees, is considered a health food by some people.
Honey Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
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 only few are widely marketed as food. They are often added to salads as garnishes. Squash blossoms are dipped in breadcrumbs and fried. Some
edible flower Edible flowers are flowers that can be consumed safely. Flowers may be eaten as vegetables as a main part of a meal, or may be used as herbs. Flowers are part of many regional cuisines, including Asian, European, and Middle Eastern cuisines.La ...
s include nasturtium,
chrysanthemum Chrysanthemums (), sometimes called mums or chrysanths, are flowering plants of the genus ''Chrysanthemum'' in the family Asteraceae. They are native to East Asia and northeastern Europe. Most species originate from East Asia and the center ...
, carnation, cattail, Japanese honeysuckle, chicory, cornflower, canna, and
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
. Edible flowers such as daisy, rose, and
violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Viol ...
are sometimes candied. Flowers such as chrysanthemum, rose, jasmine, Japanese honeysuckle, and chamomile, chosen for their fragrance and medicinal properties, are used as tisanes, either mixed with tea or on their own. Flowers have been used since prehistoric times in funeral rituals: traces of pollen have been found on a woman's tomb in the
El Miron Cave EL, El or el may refer to: Religion * El (deity), a Semitic word for "God" People * EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer * El DeBarge, music artist * El Franco Lee (1949–2016), American po ...
in Spain. Many cultures draw a connection between flowers and life and death, and because of their seasonal return flowers also suggest rebirth, which may explain why many people place flowers upon graves. The ancient Greeks, as recorded in Euripides's play '' The Phoenician Women'', placed a crown of flowers on the head of the deceased; they also covered tombs with wreaths and flower petals. Flowers were widely used in ancient Egyptian burials, and the
Mexicans Mexicans ( es, mexicanos) are the citizens of the United Mexican States. The most spoken language by Mexicans is Spanish language, Spanish, but some may also speak languages from 68 different Languages of Mexico, Indigenous linguistic groups ...
to this day use flowers prominently in their Day of the Dead celebrations in the same way that their Aztec ancestors did.


Giving

The flower-giving tradition goes back to prehistoric times when flowers often had a medicinal and herbal attributes. Archaeologists found in several grave sites remnants of flower petals. Flowers were first used as sacrificial and burial objects. Ancient Egyptians and later Greeks and Romans used flowers. In Egypt, burial objects from the time around 1540 BC were found, which depicted red poppy,
yellow Araun Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In th ...
, cornflower and lilies. Records of flower giving appear in Chinese writings and Egyptian hieroglyphics, as well as in Greek and Roman mythology. The practice of giving a flower flourished in the Middle Ages when couples showed affection through flowers. The tradition of flower-giving exists in many forms. It is an important part of Russian culture and folklore. It is common for students to give flowers to their teachers. To give yellow flowers in a romantic relationship means break-up in Russia. Nowadays, flowers are often given away in the form of a flower bouquet.


See also

*
Floral color change Floral color change occurs in flowers in a wide range of angiosperm taxa that undergo a color change associated with their age, or after successful pollination. History The first written record of the term ''floral color change'' was in 1877 wh ...
*
Flower preservation Flower preservation has existed since early Human history, history, although deliberate flower preservation is a more recent phenomenon. In the Middle East, the bones of pre-historic man were discovered with delicate wild flowers probably as a ...
* Garden *
List of garden plants This is a partial list of garden plants, plants that can be cultivated in gardens in North America, listed alphabetically by genus. A * ''Abelia'' * '' Abeliophyllum'' (white forsythia) * ''Abelmoschus'' (okra) * ''Abies'' (fir) * ''Abroma ...
* Plant evolutionary developmental biology * Plant reproductive morphology *
Sowing Sowing is the process of planting seeds. An area or object that has had seeds planted in it will be described as a sowed or sown area. Plants which are usually sown Among the major field crops, oats, wheat, and rye are sown, grasses and leg ...


Notes


References


Citations


Sources

* * * * * * *


Further reading

* * * * *


External links

*
Native Plant Information Network
{{Authority control + Plant morphology Plant reproductive system Plant sexuality Periodic phenomena Yonic symbols Pollination