A flower, (<Old French flo(u)r<Latin florem<flos), also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowering plants or angiosperms are plants of the division Magnoliophyta and one of the two major groups of seed plants, alongside the gymnosperms.
The flower structure contains the plant's reproductive organs, and its function is to produce seeds through sexual reproduction. For the higher plants, seeds are the next generation, and serve as the primary means by which individuals of a species are dispersed across the landscape. After fertilization, portions of the flower develop into a fruit containing the seeds.
Flowers are a primary example of mutualism in nature. By attracting insects and birds for pollination, flowering plants utilize them to spread their genetic material—contained in the pollen—over great distances. At the same time, the flower provides the primary source of nutrition to the pollinating organisms. As a result, whole classes of organisms—notably bees, butterflies and hummingbirds—have evolved to feed off of flowers. In their symbiotic relationship, flowers and their pollinators have evolved together, forming an inseparable bond.
Some flowers have developed intricate methods to assure that the pollen becomes attached to the insect as it seeks for nectar. This may involve color patterns, some only seen in the ultraviolet range, or a type of tunnel that the insect has to pass through to get to the nectar. Flowers emit scents that can attract the insect of choice, even aromas like decaying meat to attract flies. Both the plant and the pollinator receive benefit—-the plant is pollinated and the pollinator receives nourishment.
Some flowers, primarily those that attract birds and insects for pollination, exhibit exquisite beauty and variety in form, color, color patterns, and aroma. These flowers provide beauty and joy to humans. Flowers have been show to correlate with human well-being, including reduced stress, improved mood, enhanced self-esteem, better communication, and other benefits. (See flowers and human health below.) Thus another symbiotic relationship has formed—between flowers and humans. People have cultivated flowers to develop unique and beautiful varieties, with colors and patterns not found in nature. To better enjoy the beauty of their blooms, they have propagated flowering plants in their gardens and greenhouses, thus increasing the success of their species.
As they fulfill their reproductive purpose while providing such tangible benefits to other living things, flowers thus provide an easy-to-understand example of the principle that every entity in creation has both an individual purpose (survival and reproduction) and a whole purpose (providing value to a higher entity or cause). Contributing to the whole is the path to the flourishing of the individual. It is this principle that underlies the harmony and unity found throughout nature, and in human society as well.
Flowering plants are heterosporangiate; that is, producing two types of haploid reproductive spores. A spore is a normally haploid and unicellular reproductive mechanism produced by plants through meiosis. The pollen (male spores) and ovules (female spores) are produced in different organs, but these are together in a bisporangiate strobilus that is the typical flower.
A flower is regarded as a modified stem (Eames 1961) with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves. In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate). The stem is called a pedicel, the end of which is the torus or receptacle. The parts of a flower are arranged in whorls, cicles of similar parts radiating from approximately the same center, on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:
- calyx – the outer whorl of sepals ; typically these are green, but are petal-like in some species.
- corolla – the whorl of petals, which are usually thin, soft and colored to attract insects that help the process of pollination.
- androecium (from Greek andros oikia: man's house) – one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes.
- gynoecium (from Greek gynaikos oikia: woman's house) – one or more pistils. The female reproductive organ is the carpel: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called apocarpous). The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material. A single flower can have more than one carpel.
Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. For example, the two subclasses of flowering plants may be distinguished by the number of floral organs in each whorl: dicotyledons typically having four or five organs (or a multiple of four or five) in each whorl and monocotyledons having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.
In the majority of species, individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite—having both male and female parts.
However, in some species of plants the flowers are imperfect or unisexual—having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female, the species is regarded as dioecious. However, where unisexual male and female flowers appear on the same plant, the species is considered monoecious.
Plant species with both functional stamens and carpels on the same flower, but that mature at different times, are called dichogamous. Depending on the stage of maturity, the single flower can be either staminate or pistillate (Raven and Johnson 1996).
Some flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation. The extreme case of self-fertilization occurs in flowers that always self-fertilize, such as the common dandelion.
Conversely, many species of plants have ways of preventing self-fertilization. Unisexual male and female flowers on the same plant may not appear at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-sterile or self-incompatible. Another mechanism to prevent self-pollinization is by physically separating the anthers and stigmas. When these organs are arranged so that they do not come in contact with one anther, the pollen will be more likely to transfer to a stigma of another flower.
Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower.
In those species that have more than one flower on an axis, the collection of flowers is termed an inflorescence. In this sense, care must be exercised in considering what is a flower. In botanical terminology, a single daisy or sunflower for example, is not a flower but a flower head—an inflorescence comprised of numerous small flowers (sometimes called florets). Each small flower may be anatomically as described above (see plant sexuality section of plant article).
A floral formula is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant family rather than a particular species. The following representations are used:
Ca = calyx (sepal whorl; e.g. Ca5 = 5 sepals)
Co = corolla (petal whorl; e.g., Co3(x) = petals some multiple of three )
Z = add if zygomorphic (e.g., CoZ6 = zygomorphic with 6 petals)
A = androecium (whorl of stamens; e.g., A∞ = many stamens)
G = gynoecium (carpel or carpels; e.g., G1 = monocarpous)
x - to represent a "variable number"
∞ - to represent "many"
A floral formula would appear something like this:
- Ca5Co5A10 - ∞G1
Several other symbols are used as well. (See .)
Flower function: pollination
The function of a flower is to mediate the union of male and female gametes. The process is termed pollination. Many flowers are dependent upon the wind to move pollen between flowers of the same species. Others rely on animals (especially insects) to accomplish this feat. The period of time during which this process can take place (the flower is fully expanded and functional) is called anthesis.
Many flowers in nature have evolved to attract animals to pollinate the flower, the movements of the pollinating agent contributing to the opportunity for genetic recombinations within a dispersed plant population. Flowers that are insect-pollinated are called entomophilous (literally "insect-loving"). Flowers commonly have glands called nectaries on their various parts that attract these animals. Birds and bees are common pollinators: both having color vision, thus opting for "colorful" flowers. Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar; they may be visible to us or only under ultraviolet light, which is visible to bees and some other insects. Flowers also attract pollinators by scent. Many of their scents are pleasant to our sense of smell, but not all. Some plants, such as Rafflesia, the titan arum, and the North American pawpaw (Asimina triloba), are pollinated by flies, so produce a scent imitating rotting meat.
In any case, pollinators are attracted to the plant, perhaps in search of nectar, which they eat. The arrangement of the stamens ensures that pollen grains are transferred to the bodies of the pollinator. In gathering nectar from many flowers of the same species, the pollinator transfers pollen between all of the flowers it visits.
The flowers of other species are pollinated by the wind (for example, grasses); they have no need to attract pollinators and therefore tend not to be "showy." Wind-pollinated flowers are referred to as anemophilous. Whereas the pollen of entomophilous flowers tends to be large-grained, sticky, and rich in protein (another "reward" for pollinators), anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to insects, though it may still be gathered in times of dearth. Honeybees and bumblebees actively gather anemophilous corn (maize) pollen, though it is of seemingly little value to them.
Flowers and humans
Flowers and human health
Flowers are considered to have a number of benefits for human health (Content 2001). In addition to their use in teas and other nutritional offerings, they have been linked to human well-being in terms of reducing stress, decreasing blood pressure, enhancing self-esteem, improving ability to focus on tasks, and even reducing hospital stays. In a study by Relf, it was found that people communicate better in the presence of flowers and eat more slowly, as well as facilitate recovery from mental fatigue (Content 2001).
Haviland-Jones et al. (2005) found that flowers were powerful, positive, emotion "inducers," having a long-term positive effect on moods, social behaviors, and even memory for both males and females. Study participants reported feeling less depressed, anxious, or agitated after receiving flowers, and had a higher sense of enjoyment and life satisfaction.
There is much confusion about the role of flowers in allergies. For example, the showy and entomophilous goldenrod (Solidago) is frequently blamed for respiratory allergies, of which it is innocent, since its pollen cannot be airborne. Instead, the allergen is usually the pollen of the contemporary bloom of anemophilous ragweed (Ambrosia), which can drift for many kilometers.
In general, the brightly flowering varieties of plants, despite causing concern about allergies, are among the least likely to result in allergic symptoms. Generally, such pollens are not spread by wind, but by insects or bees.
Economic value of flowers
Flowering plants provide most of our food crops, and as a result are of enormous economic importance.
Horticulture is a field devoted to developing garden plants to provide the largest benefit to humans. On a more recreational level, gardening contributes to the growth of flowering plants on the smaller, residential scale. Floristry is the art of creating bouquets of flowers, herbs, and other botanical materials, and it includes the business and industry behind the art. Crops are grown primarily for flowers, which are then sold to retailers around the world.
The Latin words hortus (garden plant) and cultura (culture) together form horticulture, classically defined as the culture or growing of garden plants.
Horticulturists work in plant propagation, crop production, plant breeding and genetic engineering, plant biochemistry, plant physiology, and the storage, processing, and transportation of fruits, berries, nuts, vegetables, flowers, trees, shrubs, and turf. They improve crop yield, quality, nutritional value, and resistance to insects, diseases, and environmental stresses. Genetics is also used as a valuable tool in the development of plants that can synthesize chemicals for fighting disease (including cancers).
Horticulture involves five areas of study. These areas are floriculture (includes production and marketing of floral crops), landscape horticulture (includes production, marketing and maintenance of landscape plants), olericulture (includes production and marketing of vegetables), pomology (includes production and marketing of fruits), and postharvest physiology (involves maintaining quality and preventing spoilage of horticultural crops).
Horticulturists can work in industry, government, or educational institutions. They can be cropping systems engineers, wholesale or retail business managers, propagators and tissue culture specialists (fruits, vegetables, ornamentals, and turf), crop inspectors, crop production advisors, extension specialists, plant breeders, research scientists, and of course, teachers.
College courses that complement Horticulture are biology, botany, entomology, chemistry, mathematics, genetics, physiology, statistics, computer science, and communications, garden design, planting design. Plant science and horticulture courses include: plant materials, plant propagation, tissue culture, crop production, post-harvest handling, plant breeding, pollination management, crop nutrition, entomology, plant pathology, economics, and business. Some careers in horticultural science require a masters (MS) or doctoral (PhD) degree.
Gardening is the art of growing plants with the goal of crafting a purposeful landscape. Residential gardening most often takes place in or about a residence, in a space referred to as the garden. Although a garden typically is located on the land near a residence, it may also be located in a roof, in an atrium, on a balcony, in a windowbox, or on a patio or vivarium.
Gardening also takes place in non-residential green areas, such as parks, public or semi-public gardens (botanical gardens or zoological gardens), amusement and theme parks, along transportation corridors, and around tourist attractions and hotels. In these situations, a staff of gardeners or groundskeepers maintains the gardens.
In respect to its food producing purpose, gardening is distinguished from farming chiefly by scale and intent. Farming occurs on a larger scale, and with the production of saleable goods as a major motivation. Gardening is done on a smaller scale, primarily for pleasure and to produce goods for the gardener's own family or community. There is some overlap between the terms, particularly in that some moderate-sized vegetable growing concerns, often called market gardening, can fit in either category.
Flowers in the arts
The great variety of delicate and beautiful flowers has inspired the works of many poets, especially from the Romantic era. Famous examples include and William Wordsworth's I Wandered Lonely as a Cloud and William Blake's Ah! Sun-Flower:
Ah, Sun-flower weary of time,
Who countest the steps of the Sun,
Seeking after that sweet golden clime
Where the traveller's journey is done:
Where the Youth pined away with desire,
And the pale Virgin shrouded in snow
Arise from their graves, and aspire
Where my Sun-flower wishes to go.
- —William Blake, Ah! Sun-Flower
The Roman goddess of flowers, gardens, and the season of Spring is Flora. The Greek goddess of spring, flowers, and nature is Chloris.
Flowers in everyday life
In modern times, people have sought ways to cultivate, buy, wear, or just be around flowers and blooming plants, partly because of their agreeable smell. Around the world, florists sell flowers for a wide range of events and functions that, cumulatively, encompass one's lifetime:
- For new births or Christenings Lilium hybrid "Stargazer" is extremely fragrant.
- As a corsage or boutonniere to be worn at social functions or for holidays
- For wedding flowers for the bridal party, and decorations for the hall
- As brightening decorations within the home
- As a gift of remembrance for bon voyage parties, welcome home parties, and "thinking of you" gifts
- For funeral flowers and flowers for the grieving
Florists depend on an entire network of commercial growers and shippers to support this trade. To get flowers that are out of season in their country, florists contact wholesalers who have direct connections with growers in other countries to provide those flowers.
Flowers as symbols
Many flowers have important symbolic meanings in Western culture. The practice of assigning meanings to flowers is known as floriography. Some of the more common examples include:
- Red roses are given as a symbol of love, beauty, and passion.
- Poppies are a symbol of consolation in time of death. In the United Kingdom, the United States, Australia, and Canada, red poppies are worn to commemorate soldiers who have died in times of war.
- Irises/Lilies are used in burials as a symbol referring to "resurrection/life." It is also associated with stars (sun) and its petals blooming/shining.
- Daisies are a symbol of innocence.
Flowers within art are also representative of the female genitalia, as seen in the works of artists such as Georgia O'Keeffe, Imogen Cunningham, and Judy Chicago.
Flowers have been used by the well-known florist Imogen Stone to create beautiful arrangements and bouquets.
- Chowka, P. B. 2002. Sunflowers! Flowers and gardening are good for your health. Natural Healthline September 1, 2002. (Accessed August 9, 2006).
- Content, A. 2001. Studies Show Flowers can Enhance Well-Being. (Accessed August 9, 2006).
- Dickison, W. C. 2000. Integrative Plant Anatomy. San Diego, CA: Elsevier Press. ISBN 0122151704
- Eames, A. J. 1961. Morphology of the Angiosperms. New York: McGraw-Hill Book Co.
- Haviland-Jones, J., H. H. Rosario, P. Wilson, and T. R. McGuire. 2005. An environmental approach to positive emotion: Flowers. Evolutionary Psychology 3: 104-132.
- Pavord, Anna, Andrew Moor, and Christopher Garibaldi. Flower Power: The Meaning of Flowers in Art, 1500-2000. 2003. Philip Wilson Publishers. ISBN 0856675733
- Raven, P. H. and Johnson, G. B. 1996. Biology, 4th Edition. Wm. C. Brown Publishers.
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