Introduction to Flower
Flower, the part of an angiosperm (flowering plant) that contains the plant's reproductive organs. Flowers occur in many different shapes, sizes, and colors.
The cardinal flower is a tall plant with cardinal-red flowers.Interesting facts about flowersYucca flowers of the American Southwest are pollinated by female yucca moths, which lay their eggs in the flowers' seed-producing organs. The eggs hatch into caterpillars, which feed on the seeds.The night-blooming cereus is a climbing cactus with large, fragrant, white flowers that open only at night. The plant is grown in Hawaii, the West Indies, and other areas with a tropical climate.The rafflesia is the world's largest flower. It measures up to 3 feet (91 centimeters) across. Rafflesias grow in Southeast Asia. They have no stems or leaves and are parasites on other plants.Red-hot pokers have long, slender stems topped by spikes of small, brilliantly colored flowers. They belong to the lily family and may reach a height of 5 feet (1.5 meters). Red-hot pokers grow wild in Africa.Stone plants of South Africa have leaves that look like the stones among which the plants grow. Each plant has two fleshy leaves. A white or yellow flower grows in a slit between the tops of the leaves.The fly orchid of southern Ecuador has the shape and coloring of a female tachinid fly. This resemblance attracts male tachinid flies. The males pollinate fly orchids as they travel between blossoms.Gloriosa lilies have long, graceful stamens (male reproductive parts) that grow out from the petals. The stems may measure up to 6 feet (1.8 meters) tall. The flowers grow in Asia and Africa.Poinsettias have petallike leaves called bracts that surround the plants' tiny flowers. Most poinsettias have red bracts. The plants are native to Mexico and Central America.Parts of the Flower
A flower is essentially a cluster of modified leaves on a stalk known as a pedicel. The modified leaves occur in circular groups called whorls. Flowers can have up to four whorlsthe sepals, petals, carpels, and stamens. The whorls are attached to the pedicel at the receptacle, the base of the flower.
A flower with all four whorls is said to be perfect and complete. If any of the four whorls is absent, the flower is called incomplete. Flowers that lack either carpels or stamens are called imperfect, or unisexual.
The Sepalsform the outermost part of the flower. They protect the rest of the flower as it develops. In most flowers, the sepals are greenish, but in some plants they are brightly colored. The sepals of a flower may be separate or fused. The sepals are collectively called the calyx.
The Petalsin a typical flower are showy and fragrant. They attract birds and insects that help carry out the process of pollination. (This process is discussed later in this article, under the subtitle Pollination.) Flowers that are pollinated by night-flying insects are often pale in color and heavily scented. Flowers that are pollinated by the wind, such as those of grasses, may have no petals and no odor. Some flowers, such as lilies, have petals that are fused to form a tube. A flower's petals are collectively called the corolla.
In some plants, what appear to be petals are actually bracts. Bracts are not part of the flower, but are leaves positioned at its base. They may be white, as in the dogwood, or they may be brightly colored, as in the marigold.
The Carpelsmake up the female organs of the flower. A flower may lack carpels; it may have one or more separate carpels; or it may have fused carpels. Each separate carpel, or each group of fused carpels, is called a pistil. A pistil has three main parts: a stigma, a sticky structure at the top; an ovary, a bulb-shaped structure at the base; and a style, a stalklike structure connecting the two. The ovary contains one or more ovules. Within each ovule is a cell called a megaspore, which develops into an embryo sac. The embryo sac is the site of egg production and fertilization.
The Stamensare the male organs of the flower. A flower may lack stamens or it may have several stamens. Each stamen consists of a filament, or stalk, with a structure called an anther at its tip. The anther contains pollen sacs. Within each pollen sac are cells called microspores, which develop into pollen grains. When the pollen grains are fully developed, the anther breaks open to release them.
Official and unofficial flowers around the worldMany governments around the world have official or unofficial flowers. Some of these flowers are listed below.Argentina CeiboAustralia Golden wattleAustria EdelweissColombia OrchidCosta Rica Cattleya orchidEngland RoseGuatemala White nun orchidIndia LotusJapan ChrysanthemumMalaysia HibiscusMexico DahliaNetherlands TulipNew Zealand KowhaiNorthern Ireland ShamrockPhilippines Arabian jasminePortugal CarnationScotland ThistleSouth Africa Giant proteaTurkey TulipUnited States RoseWales Daffodil; LeekHow Flowers Grow
Flowers, like twigs and leaves, grow from buds. Several conditions may cause a plant to develop and maturetemperature, food supply, and length and intensity of daylight. Growth and development begin when favorable conditions cause growth-regulating substances, called hormones, to be produced.
As a flower bud swells, its floral organs tend to crowd toward the tip of the bud. The bud opens in basipetal form (from tip to base), exposing the stamens, carpels, and petals; the sepals open last.
Flowers bloom under many conditions. Most flowers bloom during the warm spring and summer months. A few, such as the crocus, begin blooming while there are still patches of snow on the ground. Other kinds, such as the chrysanthemums and zinnias, bloom in late summer and early fall.
The period of bloom varies. Many perennial plants, such as the iris and peony, bloom a few weeks only. Hybrid roses continue to bloom for a month or more, while such annual plants as the petunia and marigold bloom for several months.
The life of cut flowers varies with the species, method of cutting, and treatment. Flower stems should be cut with shears, rather than torn off, and should be placed in cold water immediately. The stems should be recut daily to permit water to reach the flowers. Most cut flowers last from a few hours to a few days. Some, such as chrysanthemums, may retain their fresh appearance for a week or more.
Pollination
Pollination is the transfer of pollen from an anther to a stigma. When a pollen grain sticks to a stigma of the same flower or of another flower of the same plant, the process is called self-pollination. For various reasons, many flowers cannot reproduce using self-pollination; for example, the anthers and stigmas may mature at different times or harmful chemical reactions may occur between pollen and stigmas of the same plant. Usually, pollen grains are carried away from the plant by wind, insects, birds, or bats. When a pollen grain sticks to a stigma of a different plant of the same species, the process is called cross-pollination.
Self-pollination produces a plant with the same genetic makeup as its parent plant. Cross-pollination, by contrast, produces a plant with a new combination of genes, some of which may give the plant a better chance of survival than it would otherwise have.
Fertilization
Fertilization is the union of sperm cells with egg cells. It occurs following pollination. When a pollen grain adheres to a receptive stigma, a pollen tube starts to grow from the grain. The pollen tube grows downward through the style into an ovule. The pollen tube carries two sperm cells from the pollen grain to the embryo sac. One sperm cell fertilizes the egg nucleus, forming the zygote. The zygote develops into the embryo, which will eventually become the plant. The other sperm cell unites with two small structures, called polar nuclei, present in the embryo sac. The polar nuclei develop into endospermtissue that nourishes the zygote and, later, the embryo.
Seed and Fruit Development
Following fertilization, the ovule develops into a seed, which contains the embryo and the endosperm. As the embryo develops inside the seed, the ovary matures into a fruit, which serves as a protective structure. After fertilization, the flower parts that were needed for pollination (sepals, petals, and stamens) wither away.
Flowers of the United States and CanadaApple (blossom) Arkansas; MichiganArbutus (Trailing)Massachusetts (Mayflower); Nova Scotia (Mayflower)Bitter rootMontanaBlack-eyed SusanMarylandBluebonnetTexasCamelliaAlabamaCarnation (Red)OhioClover (Red)VermontColumbine (White and lavender)ColoradoDogwoodBritish Columbia (Pacific); North Carolina; Virginia (American)FireweedYukonForget-me-notAlaskaGoldenrodKentucky; NebraskaHawthornMissouriHibiscusHawaii (Yellow)Indian paintbrushWyomingIrisTennessee; Quebec (Blue flag)Lady's-slipperMinnesota (Pink and white); Prince Edward IslandLilac (Purple)New HampshireLilySaskatchewan (Western red lily, also called prairie lily); Utah (Sego lily)MagnoliaLouisiana; MississippiMistletoeOklahomaMountain avensNorthwest TerritoriesMountain laurelConnecticut; PennsylvaniaOrange (blossom)FloridaOregon grapeOregonPasqueflower (Wild crocus or prairie crocus)Manitoba; South DakotaPeach (blossom)DelawarePeonyIndianaPineMaine (White pine cone and tassel)Pitcher plantNewfoundland and LabradorPoppyCalifornia (Golden)RhododendronWashington (Coast rhododendron); West VirginiaRoseAlberta (Wild rose); District of Columbia (American beauty rose); Georgia (Cherokee rose); Iowa (Wild rose); New York; North Dakota (Wild prairie rose)SagebrushNevadaSaguaro (Cactus blossom)ArizonaSaxifrageNunavut (Purple)SunflowerKansas (Native)Syringa IdahoTrilliumOntario (White)VioletIllinois; New Brunswick (Purple violet); New Jersey (Common meadow); Rhode Island; Wisconsin (Wood violet)Yellow jessamine (Carolina jessamine) South CarolinaYucca (Flower)New MexicoFlower Forms
In some plants, such as the tulip, each flower grows on its own separate stalk. In many other plants, however, flowers grow in various kinds of clusters. These clusters are called inflorescences. There are two basic kinds of inflorescences: indeterminate and determinate.
Indeterminate InflorescencesThere is no flower at the tip of the flower stalk, which continues to grow and form new flowers along its sides. The oldest flowers are at the bottom. Several kinds of indeterminate inflorescences are shown in the illustration Some Types of Inflorescences (facing page). In head inflorescences, each head appears to be a single flower but is actually many flowers. They are arranged on a horizontal, rather than vertical, axis (stalk). The corollas of the outermost flowers are often enlarged (as in the illustration) to form rays. These rays are commonly (but incorrectly) called petals.
Determinate InflorescencesThe tip of the stalk bears a flower, and other flowers develop, at a later time, below it. The cyme inflorescence shown in the illustration is typical of determinate inflorescence, which is less common than indeterminate.
Representative families of flowersSubclass DicotyledonaeBalsam family (Balsaminaceae)About 450 species of annual or perennial herbs. The flowers are bilaterally symmetrical and have 3 to 5 sepals, 5 petals, and 5 stamens. One of the sepals forms a long, spur-shaped nectary at the back of the flower. Garden balsams, touch-me-nots.Begonia family (Begoniaceae)About 900 species. Mostly perennial herbs and shrubs, with staminate and pistillate flowers on the same plant. The staminate flowers have 2 petallike sepals, 2 petals, and many stamens. The pistillate flowers have 2 or more petallike structures called tepals and a compound pistil. Begonias.Bellflower family (Campanulaceae)About 1,800 species of annual or perennial herbs. The flowers of most species have 5 sepals, 5 petals, and 5 stamens. In most species, the petals are fused along most of their length, forming a bell-shaped corolla. Bellflowers.Borage family (Boraginaceae)About 2,000 species. Mostly annual or perennial herbs; some shrubs and small trees. The flowers of most species have 5 sepals fused at the base, 5 petals fused into a tubular shape at the base, and 5 stamens. Forget-me-nots, heliotropes, lungworts.Cactus family (Cactaceae)About 2,000 species. Perennial herbs, shrubs, and trees. Most species have numerous petals, petallike sepals, and many stamens. The petals and sepals are fused at the base. Cactuses.Composite family (Asteraceae or Compositae)About 20,000 species. Mostly annual, biennial, or perennial herbs and shrubs. The flowers consist of several to many florets arranged on a head. Ageratums, arnicas, asters, black-eyed Susans, blazing stars, bonesets, calendulas, chicories, chrysanthemums, compass plants, coneflowers, cosmos, dahlias, daisies, dandelions, fleabanes, gaillardias, goldenrods, marigolds, sunflowers, thistles, tickseeds, zinnias.Crowfoot or buttercup family (Ranunculaceae)About 1,800 species. Mostly annual or perennial herbs. The majority have 5 petals--or 5 showy sepals in place of petals--and many stamens and pistils. Anemones, bugbanes, buttercups, columbines, delphiniums, hepaticas, larkspurs, marsh marigold, peonies.Evening primrose family (Onagraceae)About 650 species. Mostly annual or perennial herbs. The majority have 4 sepals, 4 petals, and 4 or 8 stamens. The sepals are fused, in many cases forming a long tube at the base of the flower. Evening primroses, fireweeds, fuchsias, godetias.Figwort or snapdragon family (Scrophulariaceae)About 3,000 species. Mostly annual, biennial, or perennial herbs. Most species have 4 or 5 fused sepals, 4 or 5 petals fused at the base, and 4 stamens. Beardtongues, foxgloves, Indian paintbrushes, monkey flowers, mulleins, slipperworts, snapdragons, toadflaxes.Gentian family (Gentianaceae)About 800 species of annual, biennial, or perennial herbs. Most species have 4 or 5 sepals, 4 or 5 petals, and as many stamens as petals. The sepals are fused at the base, forming a cup-shaped calyx. The petals are fused into a tubular shape. Gentians.Geranium family (Geraniaceae)About 750 species of annual, biennial, or perennial herbs. Most species have 5 sepals, 5 petals, and 5 or 10 stamens. Crane's-bills, geraniums, pelargoniums, stork's-bills.Mallow family (Malvaceae)About 1,500 species. Annual, biennial, or perennial herbs; some shrubs and trees. The flowers have 5 sepals, 5 petals, and many stamens. The filaments of the stamens are fused, forming a tube around the pistil. Hibiscuses, hollyhocks, mallows, rose of Sharon.Morning-glory family (Convolvulaceae)About 1,800 species. Mostly annual or perennial herbaceous vines. The flowers have 5 sepals, 5 petals, and 5 stamens. In most species, the petals are fused into a bell- or funnel-shaped corolla. Bindweeds, dodders, moonflowers, morning-glories.Mustard or cabbage family (Brassicaceae of Cruciferae)About 3,000 species. Annual, biennial, or perennial herbs. The flowers have 4 sepals and 4 petals in the shape of a cross. Most species have 6 stamens. Candytuft, cresses, mustards, rockets, stocks, sweet alyssum, wallflowers.Nasturtium family (Tropaeolaceae)About 50 species of annual or perennial herbs. The flowers of most species have 5 sepals, 5 petals, and 8 stamens. One or more of the sepals form a spur at the back of the flower. Canary creeper, nasturtiums.Nightshade family (Solanaceae)About 2,200 species. Mostly annual or perennial herbs; some shrubs and trees. The flowers have 5 fused sepals, 5 petals fused into the shape of a star or funnel; and 5 stamens. Belladonna, flowering tobacco, ground cherries, henbane, jimsonweed, petunias.Parsley or carrot family (Apiaceae or Umbelliferae)About 2,900 species. Mostly biennial or perennial herbs. In most species, the flowers are small and arranged in umbrella-shaped clusters. The florets have 5 sepals, 5 petals, and 5 stamens. Queen Anne's lace, rattlesnake masters, sweet cicely, water pennyworts.Pea family (Fabaceae or Leguminosae)About 17,000 species. Annual or perennial herbs; many shrubs and trees. The flowers of most species have 5 fused sepals, 5 petals, and 10 or many more stamens. Acacias, brooms, clovers, locoweeds, lupines, mimosas, redbuds, sweet pea, wild indigos, wisterias.Phlox family (Polemoniaceae)About 300 species. Mostly annual or perennial herbs. The flowers have 5 fused sepals, 5 petals, and 5 stamens. The petals are fused at the base. Phloxes, polemoniums.Pink family (Caryophyllaceae)About 2,100 species. Mostly annual, biennial, or perennial herbs. The flowers of most species have 5 sepals, 5 petals, and 5 or 10 stamens. Baby's-breath, campions, carnations, pinks, sweet Williams.Poppy family (Papaveraceae)About 250 species. Mostly annual or perennial herbs. The majority have 4 petals, 2 or 3 sepals, and many stamens. Bloodroot, poppies.Primrose family (Primulaceae)About 800 species of annual or perennial herbs. Most species have 5 sepals, 5 petals, and 5 stamens. The petals are fused into a tubular shape at the base. The sepals are fused into a cuplike shape. Cyclamens, loosestrifes, pimpernels, primroses.Rose family (Rosaceae)About 3,200 species of perennial herbs, shrubs, and trees. The flowers of most species have 5 sepals, 5 petals, and numerous stamens. Agrimonies, cherry laurel, cinquefoils, cotoneasters, hawthorns, mountain avens, pyracanthas, roses, spiraeas.Saxifrage family (Saxifragaceae)About 1,200 species. Mostly perennial herbs and shrubs; some small trees. The flowers of most species have 5 sepals, 5 petals, and 5 or 10 stamens. Coralbells, deutzias, hydrangeas, mock oranges, saxifrages.Violet family (Violaceae)About 850 species. Mostly perennial herbs and shrubs. The flowers have 5 sepals, 5 petals, and 5 stamens. In many species, the petal nearest the stem is larger than the others and has a hollow sac or spur at the back. Pansies, violas, violets.Subclass MonocotyledonaeAmaryllis family (Amaryllidaceae)About 1,300 species. Mostly perennial herbs. The flowers have 6 tepals and 6 stamens. All the floral parts, including the pistil, are fused at the base of the flower. Amaryllises, daffodils, jonquils, narcissuses, snowdrops.Iris family (Iridaceae)About 1,500 species of perennial herbs. The flowers have 3 petallike sepals, 3 petals, and 3 stamens. All the floral parts are fused at the base, forming a tube. Crocuses, freesias, gladioli, irises.Lily family (Liliaceae)About 650 species. Mostly perennial herbs. The flowers of most species have 6 tepals and 6 stamens. In some species, the tepals are fused at the base. Dogtooth violets, fritillaries, lilies, tulips.Orchid family (Orchidaceae)More than 20,000 species of perennial herbs with bilaterally symmetrical flowers. The flowers of most species have 3 petallike sepals; 3 petals; and 1 or 2 stamens, which are fused with the style. Fairy-slippers, lady's-slippers, orchids, pogonias.