Functions of Flower Parts

Flowers and their parts function to achieve sexual reproduction, including pollination and seed formation. After pollination is finished, the flower begins the process of seed and finally fruit formation. During pollination, pollen grains are released from the anther and carried to the stigma, either by animals (such as insects, birds, and bats) or by wind. Animals, attracted by the flower's colors or aromas, visit flowers to obtain food—either the pollen itself or the nectar, a sugary liquid produced by small glands called nectaries at the base of the flower. The animal brushes up against the anthers, which deposit pollen on the animal's body. The animal transfers the pollen to the stigma of either the same flower (self-pollination) or a second flower (cross-pollination). During wind pollination, the anthers release their pollen, which is then borne by air currents. Some of the grains are deposited on a stigma of the same or another flower.

Each pollen grain germinates and produces a slender thread of protoplasm that grows downward through the style and into the ovary. This thread, the pollen tube, contains the sperm and grows toward an ovule, where it deposits its sperm. The sperm then fuses with the egg, achieving fertilization as the first cell of the new generation is produced. The ovule matures to form a seed. At the same time, the surrounding ovary enlarges greatly, becoming a fruit as other parts of the flower recede and die off.

Because the stamens and pistils are intimately involved in reproduction, botanists refer to these as essential parts. The sepals and petals are termed nonessential parts, though in fact they remain important. The sepals and petals are sometimes called the perianth because they are found on the periphery of the anthers. A complete flower is one that has all four sets of parts. A perfect flower is one that has both androecium and gynoe-cium and is thus bisexual.

that intergrade from a sepal-like form toward the outside to a petal-like form toward the inside.

Many flowers have evolved to become simpler and are called incomplete flowers; they may lack one or more sets of parts. Apetalous flowers have only sepals, although some, such as those of the liverleaf and anemone, may be petal-like. Elms, mulberries, oaks, plantains, pigweeds, and goosefeet have sepals that remain green and are usually tiny. Naked flowers, including those of birches and willows, develop neither sepals nor petals. Grass flowers are associated with tiny green parts called bracts, which are neither sepals nor petals. The nature of the perianth is related to the way a plant undergoes

Structural Variations

Many plant species produce flowers that deviate from the idealized format. Certain lilies, for example, do not have sepals and petals that are clearly distinguishable from each other. In magnolias and some water lilies, each flower produces perianth parts

Flower Parts

In the idealized flower, the parts are free down to the receptacle. Many flowers, however, exhibit connation, in which similar parts are fused above the receptacle: for example, the petals of the morning glory, fused to form a corolla, or the sepals of carnations, which form a calyx tube. Many plants have pistils composed of individual fused segments, called carpels, while others, such as the mallow, have connate stamens, forming a stamen tube.

Variations in Flower Structure

Flowerhead (composite)

Iris flower

Ray floret (outer flower)

Flowerhead (composite)

Ray floret (outer flower)

Water Lily Pictures Parts And Functions

Disk florets (inner flowers)

Bract

Bract

Involucral bract

Glory Morning Stamen

Involucral bract

Fall (outer tepal)

Disk florets (inner flowers)

Iris flower

Fall (outer tepal)

Tepal Flower Parts

Standard (inner tepal)

Beard

Standard (inner tepal)

Beard

Spathe

Spadix

Spathe

Spadix

Spathe (modified bract)

Spurred flower

Spurred flower

Flowers take on many different forms, which have evolved to facilitate pollination by animals, wind, or water. Smaller, less showy flowers tend to be pollinated by wind (which can easily lift and carry their pollen), whereas animal-pollinated flowers have evolved colors, odors, and even structures that mimic insects or store nectar—all designed to attract the pollinators.

pollination. Flowers with a well-developed corolla or a calyx made up of petal-like sepals are attractive to animals and insects, which function to pollinate them. Apetalous and naked flowers are windpollinated; they do not need to waste their energy making showy flower parts.

Some incomplete flowers lack either the androe-cium or the gynoecium. These imperfect flowers are unisexual and fall into two categories: staminate flowers are male flowers, having only stamens and no pistils; pistillate flowers are female, having only pistils and no stamens. Forced into cross-pollination, imperfect flowers benefit the plant by preventing some of the harm inherent in self-pollination.

In the idealized flower, the parts are free down to the receptacle. Many flowers, however, exhibit con-nation, in which similar parts are fused above the receptacle. The petals of the morning glory are fused to form a funnel-shaped corolla. Carnations have connate sepals, forming a calyx tube. Many plants have pistils composed of individual fused segments, called carpels, while others, such as the mallow, have connate stamens, forming a stamen tube.

Other flowers show adnation, which involves the fusion of different parts. The stamens of phlox flowers are fused to the petals. The sepals, petals, and stamens of roses are all fused, forming a cup-shaped structure called a hypanthium. The presence of a hypanthium can be best observed in plum and cherry blossoms, whose individual sepals, petals, and stamens are attached to the rim of the hypanthium. Finally, many flowers have a hypanthium that is fused to the wall of the ovary. The result is that the sepals, petals, and stamens emerge from the top of the ovary, a good example being the apple blossom. Flowers of the latter category are said to have an inferior ovary, whereas the others have superior ovaries.

Flowers' corollas also vary: In flowers with a regular corolla, such as buttercups, lilies, and roses, all the petals are equal in size and shape, giving the flower a star shape. In flowers with irregular corollas, such as the snapdragon, pea, and orchid, one or more of the petals are unequal. Some irregular flowers, such as the violet, touch-me-not, and columbine, have a rounded, cone-shaped, or pointed extension of the corolla called a spur, which serves to store nectar.

Although not technically floral structures, color, shape, and inflorescences (the loose or dense clusters in which flowers appear on a plant) are other ways in which flowers differ, important because they allow certain pollinators to enter but exclude others. Bowl-shaped flowers are visited by a variety of insects, such as beetles and bees. Irregular flowers are typically pollinated by honeybees and bumblebees, and in some cases the insects fit the flower like a key fits a lock. Flowers with long spurs are pollinated by long-tongued insects such as moths. Color, determined by special molecules called pigments that occur within the cells of the plant, attracts different pollinators as well: red flowers are pollinated by birds, specifically hummingbirds and butterflies. White flowers are often open at night and are visited by moths. One group of plants have brown or maroon flowers and an odor of rotting flesh. These "carrion flowers" are pollinated by an array of insects, particularly beetles and flies. Interestingly, the way that humans perceive color is often different from the way that other animals perceive color. For example, xantho-phylls reflect not only yellow but also a deep violet that bees can perceive but that humans cannot.

Kenneth M. Klemow

See also: Angiosperm cells and tissues; Angiosperm evolution; Angiosperm life cycle; Angiosperm plant formation; Angiosperms; Animal-plant interactions; Flower types; Flowering regulation; Fruit: structure and types; Garden plants: flowering; Hormones; Inflorescences; Pollination; Reproduction in plants; Seeds; Shoots; Stems.

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Responses

  • kadyn kerr
    Do lilies have sepals?
    7 years ago
  • Pupa
    What are the functions of flowers?
    7 years ago
  • SEAN MIGUES
    What are the parts of sampaguita flowers?
    7 years ago
  • amethyst bolger-baggins
    What are the parts of a morning glory plant?
    6 years ago

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