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(Redirected from Flowering transition)

For other uses, see Flower (disambiguation).
"Floral" redirects here. For other uses, see Floral (disambiguation).

White flower with around nine large petals and yellow stamens
Symmetrically-shaped white and pink orchid
Circular sunflower inflorescence with yellow petals and many stamens
Very complexly-shaped white, purple, and green flower
Inflorescence of brown male corn flowers
Flower with pink petals at centre and many long red stamens.
Clockwise from top left: Magnolia grandiflora, Phalaenopsis bellina, Passiflora caerulea, Lycoris radiata, Zea mays, and Helianthus annuus.

Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants (angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, modified leaves; corolla, the petals; androecium, the male reproductive unit consisting of stamens and pollen; and gynoecium, the female part, containing style and stigma, which receives the pollen, and ovary, which contains the ovules. When flowers are arranged in groups, they are known collectively as inflorescences.

Floral growth originates at stem tips and is controlled by MADS-box genes. In most plant species flowers are heterosporous, and so can produce sex cells of both sexes. Pollination mediates the transport of pollen to the ovules in the ovaries, to facilitate sexual reproduction. It 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. Vectors transport the pollen between stamen and stigma. They may be living animals, such as birds and insects, or non-living factors such as wind and water. The colour and structure of flowers—such as nectaries and nectar guides—assist in pollination.

After pollination, both sex cells (excluding their cell walls) and their nuclei are fused together in the process of fertilisation. The result is a cell called a zygote, which has two copies of each chromosome. Through cellular and nuclear division, the zygote grows into a seed, which contains structures to assist in the future plant's survival and success. At the same time, the ovary forms into a fruit, and the other floral structures die. The function of fruit is to protect the seed and aid in dispersal. This dispersal is divided into vectors originating either from external sources, or from the plant itself. External vectors include both living things, such as animals and insects, and non-living things, such as wind and water.

Flowers evolved between 150 and 190 million years ago, during the later part of the Jurassic era and Early Cretaceous. Angiosperms replaced non-flowering seed plants in many ecosystems, as a result of flowers' greater reproductive effectiveness. In plant taxonomy, which is 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.

Etymology

Although flowers are defined as the reproductive structures of angiosperms,[1] there are many gymnosperm cones which resemble flowers. The cones of Ginkgo biloba, for example, are mostly considered to be simple strobili, and not flowers.[2] 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.[3] Flower is also commonly used to describe the whole of a plant that produces flowers.[3]

Flower is from the Middle English flour, which referred to both the ground grain and the reproductive structure in plants, before diverging in the 17th century.[4] It comes originally from the Proto-Italic *flōs ('flower'; cf. Latin flōs, flōris).[5] The Old English word for flower was blossom,[4] which is still in use, but refers especially to the flowers of edible fruit trees, and not to the whole flowering plant.[3] Flower, bloom, and blossom are all cognates and are derived from the Proto-Indo-European word *bʰleh₃ōs ('blossoming').[5] Both bloom and blossom refer to flowers as well as the state of flowering; as in the phrases: in bloom or in blossom.[3]

Function

The principal purpose of a flower is reproduction,[6] both of the individual and of the species.[7] Flowers not only develop and produce spores (reproductive units), gametes (sex cells), zygotes (fertilised cells), and seeds, but also aid in their effective dispersal.[8] Sexual reproduction between plants results in evolutionary adaptation, which improves species survival. For this reason, plants favour cross-pollination. Facilitating this process is a key function of flowers and is often reflected in their form and structure.[8] Specific structures to attract pollinators (animals that transport pollen), for example, are the most common adaptations.[9]

Structure

Main article: Floral morphology
Diagram of flower structure, with arrows pointing to major components
Diagram of flower structure

The structure of a flower, termed its morphology,[10] 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,[11] flower is made up of four kinds of structures arranged in sets (whorls) around the tip of a short stalk or axis, called a receptacle.[12] The four main whorls (starting from the base of the flower or lowest node and working upwards) are the calyx, corolla, androecium, and gynoecium.[13]

Vegetative

Main article: Perianth

The vegetative part of the flower, known collectively as the perianth, consists of calyx, the modified outer leaves, and corolla, the petals. The receptacle is the thickened part of the flower stalk, called the pedicel, which supports all of the other flower structures.[11][14]

Calyx

The sepals, collectively called the calyx, are modified leaves that occur on the outermost whorl of the flower. They are leaf-like,[15] in that they have a broad base, stomata (pores), chlorophyll (green pigment), and may have stipules (outgrowths from the leaf stem). Sepals are often waxy and tough, and grow quickly to protect the flower as it develops.[14][16] They may be deciduous (fall off at maturity), but will more commonly grow on to assist in fruit dispersal. If the calyx is partially or completely fused it is called gamosepalous.[16][17]

Corolla

The petals, collectively called the corolla,[18] 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.[19] If the corolla is fused together it is called sympetalous.[20] In some flowers, petals and sepals are indistinguishable and are known as tepals.[21] Petals also tend to have patterns only visible under ultraviolet light, which is visible to pollinators but not to humans.[19]

Reproductive

Diagram of an anther in cross section. 1: Filament; 2: Theca; 3: Connective (the conducting vessels in red); 4: Pollen sac (also called sporangium)
Diagram showing the positions of the major angiosperm ovule features
Diagram of angiosperm ovule
Main article: Plant reproductive morphology

All flowering plants are heterosporous, that is, every individual plant produces two types of spores. Meiosis is a type of cell division that occurs in angiosperms to produce microspores and megaspores; the precursors to pollen and embryo sacs (the gametophyes). Microspores are produced by meiosis inside anthers and megaspores are produced inside ovules contained within an ovary.

Anthers, the tips of the male part of the flower (containing the pollen sacs),[18] typically consist of four microsporangia (tissues that produce microspores) and an ovule in an integumented (protected by a layer of tissue) megasporangium (tissue that produces a megaspore). Both types of spores develop into gametophytes (organisms that lead to creation of sex cells) inside sporangia. As with all heterosporous plants, the gametophytes also develop inside the spores, i.e., they are endosporic.[22]

Male

The androecium, consisting of 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 (sheaths), connected to a filament, or stalk.[18] The anther contains microspores which become pollen, the male gametophyte, after undergoing meiosis (cell division). 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.[19][20] In general, plants have only one type of stamen, but there are plant species where the flowers have two types; a typical one, and one with anthers that produce sterile pollen meant to attract pollinators. These plants are called heterantherous.[23]

Female

The gynoecium, consisting of one or more carpels, is the female part of the flower and found on the innermost whorl.[18] Each carpel consists of: a stigma, which receives pollen; a style, the stalk; and an ovary, which contains the ovules (containing the female gametophytes). Carpels may occur in one or more whorls, and when fused are often described as a pistil. Inside the ovary, the ovules are attached to the placenta by structures called funiculi.[24][25]

Variation

Diagram of flower sex variation in plants
Diagram showing that: hermaphrodite flowers have both sexes, monoecious plants have sexes on different flowers, and dioecious plants have either just female or just male flowers.
Two Hydrangea flowers, the left one is a normal blue colour, but the right one has green petals, an example of phyllody.
A healthy (left) and infected (right) Hydrangea flower. Phytoplasma has caused the flower to develop leaves in place of petals, an example of phyllody.[26]

Although most plants have flowers with four whorls—calyx, corolla, androecium, and gynoecium—and their typical sub-structures, angiosperms exhibit wide variation in floral structure.[11][27] This variation encompasses all aspects of the flower, including size, shape, and colour.[11] Additionally, 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—known as incomplete—or parts may be modified into other functions or look like what is typically another part.[11][28][29] In some families, such as the grasses, the petals are greatly reduced; in many species, the sepals are colourful and petal-like. Other flowers have modified petal-like stamens; the double flowers of peonies and roses are mostly petaloid stamens, for example.[30]

Many flowers have symmetry. 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.[31][32]

Flowers may be directly attached to the plant at their base (sessile—the supporting stalk or stem is highly reduced or absent).[33] The stem or stalk subtending a flower is called a pedicel. The main axis or stalk of an inflorescence (a cluster of flowers)[11] is called a peduncle.[34] There are several structures, found in some plants, that resemble flowers or floral organs, but often only in an ambiguous way. These include: coronas, crown-like outgrowths;[35] phyllody, leafy flower parts;[36] and pseudonectaries.[37]

In the majority of species, individual flowers have both carpels and stamens. These flowers are synonymously 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.[38] Many flowers have floral nectaries, which are glands that produce a sugary fluid (nectar) used to attract pollinators. They are not considered as an organ on their own.[39]

Inflorescence

Cluster of purple flowers, collectively called an inflorescence
Inflorescence of Eryngium flowers
Floral diagram and formula for a Convolvulus flower, showing the number and orientation of the floral organs.
Floral diagram and formula for a Convolvulus flower
Main article: Inflorescence

In those species that have more than one flower on an axis, the collective cluster of flowers is called an inflorescence.[11] Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. These are known as pseudanthia.[40] Most members of the very large composite Asteraceae group have this morphology. A single daisy or sunflower, for example, is not a flower but a flower head—an inflorescence composed of numerous flowers or florets (small reduced flowers).[41] An inflorescence may include specialised stems and modified leaves known as bracts and smaller bracteoles.[12]

Floral diagrams and formulae

Main articles: Floral formula and Floral diagram

A floral formula is a way to represent the structure of a flower using letters, numbers, and symbols, presenting substantial information about the flower in a compact form. It can represent a taxon 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 they convey the same information.[42][43]

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 fusion and symmetry, and structural details.[44]

Development

A flower develops on a modified shoot or axis from a determinate (grows to a set size) apical meristem (stem tip). It has compressed internodes (gaps between attachment points), bearing structures that in classical plant morphology are interpreted as highly modified leaves.[45] Developmental studies have shown that floral organs can originate from modified stems (caulomes), leaves (phyllomes), and shoots. This suggests a continuum in floral evolution, in which intermediate structures blur the lines between organs.[46][47] All aspects of flower morphology and function are controlled by a gene regulatory network of MADS-box genes and associated proteins.[48][49]

Transition

The transition to flowering is one of the major phase changes that a plant makes during its life cycle.[11] 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 endogenous (internal) and environmental cues such as: changes in levels of plant hormones (such as gibberellins),[50] seasonable temperature, and photoperiod (daylight) changes.[51] Many perennial (more than two-year lifespan) and biennial (two-year lifespan) plants require vernalisation (cold exposure) to flower.[50][52][53] The molecular interpretation of these signals is through the transmission of a complex signal known as 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.[54]

The first step of the transition is the transformation of the vegetative stem primordia (groups of cells) into floral primordia. This occurs as biochemical changes take place to change the cellular differentiation of leaf, bud and stem tissues into tissue that will grow into the reproductive organs. The sides of the growing stem tip develop bulges, which then grow into the sepals, petals, stamens, and carpels.[55] Once this process begins, in most plants, it cannot be reversed and the stems develop flowers—even if the initial event was dependent on some environmental cue, which is no longer present.[56]

Diagram that shows that the C gene results in carpels, C + B genes results in stamens, A + B genes results in petals, and the A gene results in sepals.
Diagram of the ABC model of development

Organ development

Main article: ABC model of flower development

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.[57] It describes how three groups of genes—A, B, and C—are responsible for the development of flowers. These three gene groups' activities interact in a combinatorial manner 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.[58]

Pollination

Main article: Pollination
A fly pollinating a yellow flower with yellow stamens
A hoverfly pollinating Oxalis pes-caprae
A golden-coloured bat using its tongue to feed on the nectar of a yellow flower
A grey-headed flying fox feeding on nectar
A black and yellow flower shaped like a female bee
Ophrys apifera, which has evolved to mimic a female bee[59]
A hummingbird pollinating a small red flower
Mexican violetear, Colibri thalassinus, pollinating a flower
Various examples of biotic pollination

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.[14] Pollination is this movement of pollen from the male parts (anthers) to the female parts (at the stigma).[60] 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.[8][61] The period during which pollination can take place (when the flower is fully expanded and functional) is called anthesis.[62]

Flowering plants usually face evolutionary pressure to optimise the transfer of their pollen, and this is typically reflected in their floral morphology and reproductive strategies.[63][64] The mechanisms by which pollen is transferred between plants are called vectors. Around 80% of flowering plants make use of biotic or living vectors. Others use abiotic (non-living) vectors, or some combination of the two.[65][66]

Biotic pollination

Flowers that use biotic vectors attract and use animals to transfer pollen from one flower to the next. Often they are specialised in shape and have an arrangement of 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).[9] Flowers most commonly employ insects (entomophily),[67] but also: birds (ornithophily), bats (chiropterophily), lizards (saurophily),[68] other mammals,[69] snails and slugs (malacophily),[67] and in rare cases crustaceans and worms.[69]

Most commonly, flowers are insect-pollinated, known as entomophilous; literally "insect-loving" in Greek.[70] Flowers commonly have glands called nectaries on various parts that attract animals, such as insects, looking for nutritious nectar.[71] Some flowers have glands called elaiophores, which produce oils rather than nectar.[72] Birds and bees have colour vision, enabling them to seek out colourful flowers.[73] Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar; they may be visible only under ultraviolet light, which can be seen by bees and some other insects.[74]

Pollinator relationships

Further information: Pollination syndrome

Many flowers have close relationships with one or a few specific pollinating organisms. They may, for example, attract only one specific species of insect and therefore rely on that insect for successful reproduction. This close relationship is an example of coevolution, as the flower and pollinator have developed together over a long period to match each other's needs.[75] 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.[76]

A catkin in which the pollen has yet to be released from the red sections
A male catkin of Populus tremula, which uses the wind to transport pollen to female flowers
A white "open-banana" shaped flower, floating on the surface of the water
The female flower of Enhalus acoroides, which is pollinated by the flow of water

Abiotic pollination

Main articles: Anemophily and Hydrophily

Flowers that use abiotic (non-living) vectors use the wind or, much less commonly, water, to move pollen from one flower to the next.[66] Wind-dispersed (anemophilous) 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.[77] 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.[78][79]

Fertilisation and seed development

Diagram illustrating the process of fertilisation, where the ovules are fused with the sperm cells within pollen grains
A flower's ovules are fertilised by sperm cells from pollen grains.

Fertilisation

Fertilisation, also called syngamy, is the fusion of the male and female sex cells, or gametes, to produce a zygote.[7] It 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 into one synergid (specialised guiding cell).[80]

After pollen enters the synergid, 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 (jelly-like substance that fills cells). The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote; a diploid (two copies of each chromosome) cell.[7][80] In angiosperms, a process known as double fertilisation, which involves both karyogamy and plasmogamy, occurs. In double fertilisation 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, they result in a large endosperm (nutrient tissue) nucleus which is triploid.[80]

Seed and fruit development

Main articles: Seed development and Fruit § Development
Diagram showing the processes of fruit and seed development, as well as seed dispersal, of a pea plant
Development of seeds (peas) and fruit (pod) from pea flower

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,[81] while the other becomes the suspensor; a structure which forces the embryo into the endosperm and is later undetectable. Two small primordia (groups of cells) also form at this time, that later become the cotyledon (initial leaf), which is used as an energy store. The next stage is called the torpedo stage and involves the growth of several key structures, including:radicle, the embryotic root; epicotyl, the embryotic stem; and hypocotyl, the root or shoot junction. In the final step vascular tissue develops around the seed.[82]

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, sepals, stamens, and petals. The fruit contains three main structures: the exocarp, or outer layer; the mesocarp, or the fleshy part; the endocarp, or innermost layer; and the pericarp, the fruit wall. The size, shape, toughness, and thickness varies among different dry and fleshy fruits. This is because it is directly connected to the method of seed dispersal, which is the purpose of fruit; to encourage or enable the seed's dispersal and protect the seed while doing so.[82][83]

Seed dispersal

Main articles: Biological dispersal and Seed dispersal

Following the pollination of a flower, fertilisation, and finally the development of a seed and fruit, a mechanism (termed a vector) is typically used to disperse the fruit away from the plant.[84] In angiosperms, seeds are dispersed away from the plant so as to not force competition between the mother and the daughter plants,[85] as well as to enable the colonisation of new areas. Vectors can generally be divided into two categories: allochory (an external vector) or autochory (an internal vector); usually the plant itself.[86][87] Allochory can be undergone either by living (biotic) vectors such as birds or bats, or by non-living (abiotic) vectors such as water and wind.[86][88]

Evolution

Further information: Evolutionary history of plants § Flowers, and Floral biology
Fossil of an early flowering plant
Archaefructus liaoningensis, one of the earliest known flowering plants
A plant with small white flowers
Amborella trichopoda may have characteristic features of the earliest flowering plants.[89]

Flowers originated between 150 and 190 million years ago, during the later part of the Jurassic era and Early Cretaceous. Prior to the advent of flowers, plants reproduced using cones (as in gymnosperms),[90] spores, or sporangia.[91] The development of flowers allowed angiosperms to replace many other seed plants—such as Pinales, Cycads, Gnetophyta and Ginkgoales,[92] as a result of their greater seed security and reproductive speed.[93] There is debate over whether the evolutionary process of forming the components which eventually became the first flower, can be entirely described as gradualistic (occurring step by step). Evidence suggests, however, that at least some of the process can be attributed to sudden, random changes; these are called saltations. These include homeotic mutations, which change the position of an appendage.[94]

One example of hard evidence for early flowers is Archaefructus liaoningensis from China; dated to around 125 million years old.[95] Even earlier from China is the 125–130 million years old Archaefructus sinensis. In 2015 Montsechia vidalii, discovered in Spain, was claimed to be 130 million years old.[96]

Angiosperms are a sub-group of spermatophytes (seed plants), and of these, the living species are regarded as a more recent ancestor of the older angiophytes.[97] Aspects of flower morphology can be split into three evolutionary groups based on when they first occurred: pre-angiophyte, angiophyte, and angiosperm. Pre-angiophyte features include the ovules, seeds, microsporangia, and the outer male and inner female organs. The first three of these are shared by all seed plants, while the latter two must be considered pre-angiophyte because they exist in Gnetophyta (division of non-flowering gymnosperms).[98]

The angiophytes' most significant evolutionary developments were the carpel (female flower parts) and structure of the thecae (sheaths covering pollen sacs). The integument, a part of the carpel, covers the ovule or ovules and protects them through either secretion or postgenital fusion; the combining of different organs. The latter aspect is unique to them and is effective at sealing the carpel shut. Thecal structure refers to the structure of angiosperm stamens, with their four microsporangia that are almost always divided into two thecae. The evolutionary reason for this is uncertain, but may be because it is more efficient at presenting pollen than a single sporangium.[99] Within the angiosperms, some plants have flowers with features not found in other angiosperms. These include: petals; syncarpy; sympetaly and floral tubes; floral spurs; tenuinucellar (tissue surrounding embryo sac is thin); and unitegmic (only one integument) ovules.[100]

Coevolution

Main article: Coevolution
Two small beetle-like insects in a pink and yellow flower, feeding on the pollen and thereby indirectly pollinating it.
Hypothetical life restoration of Angimordella burmitina, an early (99 Mya) insect pollinator[101]

A key driving evolutionary force in many flowers is coevolution, where pollinator and flower evolve with one-another,[102] 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. Flowers may evolve in such a way so as to make pollination by specific species easier, thus providing greater efficiency and also ensuring higher rates of pollination. The latter is a result of receiving less pollen from other species.[75][77] Fossils of the beetle Angimordella burmitina, which is at least 99 million years old, show evidence of adaptions for pollination, likely specific to just one species. These include hairs spaced and shaped to efficiently collect pollen and hind legs capable of moving from one flower to the next.[101] There is significantly more evidence of insect pollination in gymnosperms than in angiosperms during this (Cretaceous) period.[103]

Colour

Diagram showing how buttercups produce their colour by using pigments and structural colouration
Buttercup petals exploit both yellow pigment and structural colouration.
Diagram showing how photonic crystals diffract light waves to produce an effect
The diffraction mechanism of a photonic crystal composed of nanospheres

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.[104] These colours are produced principally by biological pigments, which are molecules that can absorb and retain energy from light, for just a few microseconds (one millionth of a second) at maximum.[105] That is, they reflect only specific wavelengths of light.[106]

Specific pigments, and so colours, provide different benefits to the plant. Tetrapyrroles (green, blue-green, red) assist in both flower detection and photosynthesis; carotenoids (yellow, orange, red) assist in both signalling and detection, as well as storage and preventing degradation by photo-oxidation (degradation by oxygen and light); flavonoids (colourless, white, pale yellow, red, purple, blue) provide detection and defence against ultraviolet (UV) damage; and betalains (red, purple, blue) provide benefits similar to some flavonoids.[107]

Colour helps pollinators to detect not only flowers in general, increasing the overall rates of pollination,[107] but also specific flowers with which they have coevolved. These specific flowers may be adapted to provide maximum efficiency to the pollinator and so are preferred.[75] The largest contributors to flower pollination come from bees, of which are there more than 20,000 species. Bees do not see like humans, and are capable of seeing the ultraviolet range of light. As a result, many petals contain carotenoids and flavonoids, because of their ultraviolet reflective and absorptive properties, respectively. This means they stand out against green colours, which bees perceive as a wash of greys.[108]

Another mechanism that flowers use to produce colour, or colour-effects, is structural colour. Some tulips, for example, exhibit iridescence (shimmering effect) by producing ridged cuticles (protective layers of leaves) that split light into their constituent wavelengths by using diffraction grating.[109] Also present in some flowers are photonic crystals. For example, edelweiss flowers have small hairs shaped like hollow tubes which diffract light and protect against UV radiation.[110] The colour of flowers can also change; sometimes this is 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.[111]

Taxonomy

Further information: Plant taxonomy and Linnaean taxonomy
Diagram of 24 different flowers
Linnaeus's diagram of 24 classes of sexual systems, from Systema Naturae
Diagram with species at the end of branches on a phylogenetic tree
Maximum likelihood diagram of a phylogenetic tree of orchids in the genus Vanilla
Classical and modern approaches to angiosperm taxonomy

In plant taxonomy, which is the study of plant classification and identification, the morphology of plants' 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,[112] the foundation of the modern science is based on works in the 18th and 19th centuries.[113]

Carl Linnaeus's 1753 book Species Plantarum laid out his (artificial) system of classification as well as the concept of binomial nomenclature, the latter of which is still used around the world today.[113][114][note 1] He identified 24 classes, based mainly on the number, length, and union of the stamens. The first ten classes follow the number of stamens directly (Octandria have 8 stamens etc.),[114][115] 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).[115][116]

The French botanist Antoine Laurent de Jussieu's 1789 work Genera plantarum 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.[116][117] The next most major system of classification came in the late 19th century from the botanists Joseph Hooker and George Bentham. They built on the earlier works of de Jussieu and Augustin Pyramus de Candolle, and devised a system in which plants were divided at the highest level by the number of cotyledons and the nature of the flowers, before falling into orders (families), genera, and species. This system of classification was published in their Genera plantarum in three volumes between 1862 and 1883.[118]

In 1963, the biologists Robert Sokal and Peter Sneath created the method of numerical taxonomy, which differentiates taxa based on their tabulated morphological characteristics.[119] While earlier methods, such as Linnaeus's, used morphological features, many botanists today use more phylogenetic methods through the use of genetic sequencing, cytology (study of cells), and palynology (study of pollen). This comes as a result of advancement in DNA-related science.[120] Despite this, morphological characteristics such as the nature of the flower and inflorescence still make up the bedrock of plant taxonomy.[121][122]

Uses

Further information: Flowering plant § Human uses, and Human uses of plants

Flowers have been used by humans all over the world for thousands of years for a variety of purposes, including: decoration, medicine, food, perfumes,[123] and essential oils. Many flowers are edible and are often used in drinks and dishes, such as salads, for taste, scent, and decoration.[124] Some flowers are commonly described as vegetables, when in fact they are actually inflorescences, bracts, or stems of flowers. These include: broccoli, cauliflower, and artichoke. Flowers may be eaten freshly after being picked, termed floriphagia, or dried and eaten later.[125] 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.[126]

Between 3 and 8% (around 1500) of all crops are pollinated by insects. In this way, flowers contribute a total economic value of around $361 bn (2015 estimate) to the world economy.[127] In addition, most crop plants are angiosperms,[128] and they produce much of the most common crop products—such as seeds and fruits;[7] around half of all cropland is used to grow three angiosperms; rice, wheat, and corn.[129] Some flowers are steeped with or without Camellia sinensis (tea plant) to produce flower tea.[130] Essential oils and other flower extracts are widely used in herbal medicines and decoctions because they contain phytochemicals and may have anti-microbial effects.[131]

In culture

"I know a bank where the wild thyme blows,
Where oxlips and the nodding violet grows,
Quite over-canopied with luscious woodbine,
With sweet musk-roses and with eglantine:
There sleeps Titania sometime of the night,
Lull’d in these flowers with dances and delight;"

Poets often use flowers as imagery, as in this excerpt from Shakespeare's A Midsummer Night’s Dream
Further information: Human uses of plants § Symbolic uses

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.[132][133] Flowers are associated with burial in many cultures, and are often placed by headstones to pay respect.[134][135] They are also placed by statues or temples of religious or other figures—sometimes formed into floral wreaths.[136][137] In some places, the dead are buried covered in flowers or on a bed of flowers.[138] They are also associated with love, and given to others in many places for this reason.[139] As a result of economic forces, plants are bred for longer lasting, more beautiful, or colourful flowers.[140]

Flowers feature extensively in art across a variety of mediums, and different flowers are ascribed symbolic meanings.[141][142] For example, violets may represent modesty, virtue, or affection.[143] 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.[144] In literature, flowers feature in imagery of places and as metaphors for pleasure, beauty, and life.[145]

Notes

  1. ^ His earlier works: Systema Naturae (1735) and Genera plantarum (1737) were also influential in the field.[114]

References

  1. ^ Sinclair 1998, p. 589.
  2. ^ Rudall et al. 2011, pp. 151–152.
  3. ^ a b c d Sinclair 1998, p. 169.
  4. ^ a b Cresswell 2010, p. 172.
  5. ^ a b de Vaan 2008, pp. 227–228.
  6. ^ Beekman et al. 2016, p. 5.
  7. ^ a b c d Pandey 2023, p. 7.
  8. ^ a b c Mauseth 2016, p. 238.
  9. ^ a b Mauseth 2016, pp. 239–240.
  10. ^ Sinclair 1998, p. 1012.
  11. ^ a b c d e f g h Pandey 2023, p. 15.
  12. ^ a b De Craene 2010, p. 4.
  13. ^ De Craene 2010, p. 3.
  14. ^ a b c Mauseth 2016, p. 225.
  15. ^ Pandey 2023, p. 16.
  16. ^ a b De Craene 2010, p. 7.
  17. ^ Sinclair 1998, p. 630.
  18. ^ a b c d Pandey 2023, p. 17.
  19. ^ a b c Mauseth 2016, p. 226.
  20. ^ a b De Craene 2010, p. 8.
  21. ^ Mauseth 2016, p. 786.
  22. ^ Leins 2010, pp. 1–6.
  23. ^ Peach & Mazer 2019, p. 598.
  24. ^ Mauseth 2016, p. 229.
  25. ^ De Craene 2010, p. 14.
  26. ^ Namba 2019, p. 403.
  27. ^ Sattler 1973, p. xiv.
  28. ^ Eames 1961, pp. 12–13.
  29. ^ Endress 1996, p. 11.
  30. ^ Reynolds & Tampion 1983, p. 41.
  31. ^ De Craene 2010, p. 25.
  32. ^ Weberling 1992, pp. 17–19.
  33. ^ Mauseth 2016, p. 243.
  34. ^ De Craene 2010, p. 410.
  35. ^ Kostyun, Robertson & Preston 2019, p. 1.
  36. ^ Namba 2019, pp. 403 & 408.
  37. ^ Delpeuch et al. 2022, p. 10.
  38. ^ Mauseth 2016, p. 239.
  39. ^ De Craene 2010, p. 21.
  40. ^ Baczyński & Claßen-Bockhoff 2023, p. 179.
  41. ^ Mauseth 2016, p. 228.
  42. ^ De Craene 2010, p. 38.
  43. ^ Sharma 2009, pp. 165–166.
  44. ^ De Craene 2010, p. 36.
  45. ^ Eames 1961, p. 88.
  46. ^ Sattler & Jeune 1992, p. 249.
  47. ^ Rutishauser 1989, pp. 60–63.
  48. ^ Pandey 2023, pp. 18–19.
  49. ^ Ng & Yanofsky 2001, p. 186.
  50. ^ a b Pandey 2023, p. 21.
  51. ^ Ausín et al. 2005, pp. 689–705.
  52. ^ Xu & Chong 2018, p. 997.
  53. ^ Li et al. 2022, p. 62.
  54. ^ Turck, Fornara & Coupland 2008, p. 573.
  55. ^ Kwiatkowska 2006, pp. 571–572.
  56. ^ Adrian, Torti & Turck 2009, p. 628.
  57. ^ Pandey 2023, p. 19.
  58. ^ Mauseth 2016, pp. 392–395.
  59. ^ Osiadacz & Kręciała 2014, p. 12.
  60. ^ Walker 2020, p. 9.
  61. ^ Pandey 2023, p. 136.
  62. ^ Walker 2020, p. 120.
  63. ^ Pandey 2023, p. 140.
  64. ^ Friedman 2011, pp. 911–913.
  65. ^ Walker 2020, p. 55.
  66. ^ a b Ackerman 2000, pp. 167–185.
  67. ^ a b Sarma et al. 2007, p. 826.
  68. ^ Walker 2020, pp. 69–83.
  69. ^ a b Ollerton 2017, p. 356.
  70. ^ Walker 2020, p. 81.
  71. ^ Walker 2020, pp. 112–113.
  72. ^ Schäffler & Dötterl 2011, pp. 409–424.
  73. ^ Walker 2020, pp. 107–108.
  74. ^ Walker 2020, p. 121.
  75. ^ a b c Mauseth 2016, p. 240.
  76. ^ Bawa 1990, p. 415.
  77. ^ a b Mauseth 2016, p. 241.
  78. ^ Knuth, Müller & Ainsworth Davis 1906, pp. 68–72.
  79. ^ Höcherl et al. 2012, pp. 278–285.
  80. ^ a b c Mauseth 2016, p. 234.
  81. ^ Pandey 2023, p. 199.
  82. ^ a b Mauseth 2016, pp. 235–237.
  83. ^ Pandey 2023, p. 262.
  84. ^ Mauseth 2016, p. 248.
  85. ^ Bowler & Benton 2005, pp. 205–225.
  86. ^ a b Pijl 1972, p. 71.
  87. ^ Howe & Smallwood 1982, pp. 201–228.
  88. ^ Forget 2005, p. 21.
  89. ^ Goremykin et al. 2003, p. 1499.
  90. ^ Chanderbali et al. 2016, p. 1257.
  91. ^ Krishnamurthy 2015, p. 410.
  92. ^ Chanderbali et al. 2016, p. 1256.
  93. ^ Chanderbali et al. 2016, p. 1255.
  94. ^ Becker, Alix & Damerval 2011, p. 1427.
  95. ^ Friis et al. 2003, p. 369.
  96. ^ Gomez et al. 2020, pp. 1–2.
  97. ^ Endress 2001, p. 106.
  98. ^ Endress 2001, p. 107.
  99. ^ Endress 2001, pp. 107–108.
  100. ^ Endress 2001, pp. 108–111.
  101. ^ a b Bao et al. 2019, p. 24708.
  102. ^ Mauseth 2016, p. 765.
  103. ^ Bao et al. 2019, p. 24707.
  104. ^ Miller, Owens & Rørslett 2011, pp. 282–284.
  105. ^ Miller, Owens & Rørslett 2011, p. 284.
  106. ^ Sun, Bhushan & Tong 2013, p. 14864.
  107. ^ a b Miller, Owens & Rørslett 2011, p. 286.
  108. ^ Miller, Owens & Rørslett 2011, p. 287.
  109. ^ Sun, Bhushan & Tong 2013, p. 14873.
  110. ^ Sun, Bhushan & Tong 2013, p. 14876.
  111. ^ Miller, Owens & Rørslett 2011, pp. 290–293.
  112. ^ Sharma 2009, p. 8.
  113. ^ a b Sharma 2009, p. 10.
  114. ^ a b c Sharma 2009, p. 21.
  115. ^ a b Rouhan & Gaudeul 2021, p. 9.
  116. ^ a b Sharma 2009, p. 22.
  117. ^ Rouhan & Gaudeul 2021, p. 11.
  118. ^ Sharma 2009, pp. 24–27.
  119. ^ Rouhan & Gaudeul 2021, p. 12.
  120. ^ Rouhan & Gaudeul 2021, p. 14.
  121. ^ Sharma 2009, p. 11.
  122. ^ Sharma 2009, p. 96.
  123. ^ Buchmann 2016, p. 186.
  124. ^ Santos & Reis 2021, p. 438.
  125. ^ Santos & Reis 2021, p. 439.
  126. ^ Zinn 2019, p. 5.
  127. ^ Hanley et al. 2015, p. 1.
  128. ^ Castel et al. 2024, p. 92.
  129. ^ Delaney & von Wettberg 2023, p. 2.
  130. ^ Santos & Reis 2021, p. 441.
  131. ^ Voon, Bhat & Rusul 2012, p. 34.
  132. ^ Buchmann 2016, p. 84.
  133. ^ Goody 1993, p. 29.
  134. ^ Buchmann 2016, p. 105.
  135. ^ Goody 1993, p. 285.
  136. ^ Bhati, Dubey & Singh 2021, p. 479.
  137. ^ Buchmann 2016, p. 113.
  138. ^ Buchmann 2016, p. 106.
  139. ^ Buchmann 2016, p. 111.
  140. ^ Buchmann 2016, p. 136.
  141. ^ Buchmann 2016, p. 210.
  142. ^ Goody 1993, p. 232.
  143. ^ Buchmann 2016, p. 209.
  144. ^ Buchmann 2016, p. 218.
  145. ^ Buchmann 2016, p. 221.

Bibliography

  • The dictionary definition of flower at Wiktionary
  • Media related to Flowers at Wikimedia Commons
  • Quotations related to Flowers at Wikiquote
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