Botany

Anatomy of a Flower



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Many flowering plants produce showy, flamboyant blooms; even more so when the plant is created by a horticulturist rather than by Mother Nature. The feature typically accentuated in showy flowers is the number of petals.

But flowers are much more than a collection of petals. A flower is the reproductive structure of a flowering plant, and, if fertilized, will become the fruit and seeds for the next generation. The following is a list of terms and definitions describing the parts of a mature flower.

*The Flower Stalk*

The flower is attached to the plant atop a part of the plant commonly called the stem. The scientific terms associated with the stem are:

~ Pedicel: The flower stalk.

~ Receptacle: The point of attachment between the flower and the pedicel.

The different parts of a flower are arranged in whorls of modified leaves attached to the receptacle.There are typically four whorls on a flower. From the outermost to the innermost are the sepals, petals, androecium (male parts) and, at the center, the gynoecium (female parts).

*Outer Whorls - Flower Petals and Sepals*

~ Calyx (Sepals): The calyx is the outermost whorl. It is composed of many sepals. Sepals look like something between a petal and a leaf, and function as the green covering that protects the flower while it is developing, before it blooms.

~ Corolla (Petals): Moving inward, the next whorl is composed of petals which, all together, are considered the corolla. Petals are leaves that have been modified to attract insects into the flower. They may have guidelines on them (like little runways, leading to the nectar) and may be scented.

~ Floral Bracts: Like petals and sepals, bracts are modified leaves. Bracts simulate petals. The red bracts on poinsettias and the white or pink bracts on dogwoods are two examples.

~ Tepals: When sepals and petals look alike (such as in wind pollinated flowers), they are individually considered tepals, which collectively are referred to as the perianth.

*Inner Whorls - The Male and Female Floral Parts*

~ Male Parts of a Flower: Stamens are the individual male parts of a flower. A stamen is composed of a filament (the stalk) and anther. The anthers contain pollen grains (microsporangium, a.k.a. flower sperm). The androecium is the entire male floral reproductive structure, and may consist of many stamen. The male floral parts comprise the third whorl of a flower.

~ Female Parts of a Flower: Female parts occur at the flower's center, the fourth whorl, and are surrounded by the male floral parts.

* Gynoecium: General term for the female reproductive structure on a flower; which consists of one or more pistils.

* Pistil: The female organ of a flower, composed of one or more carpels.

* Carpel: In flowers with only one carpel, the term pistil is synonymous with the term carpel. However, some flowers have several (compound) carpels. An individual carpel consists of three parts, the stigma, style and ovary.

Confused? Lets put it all together. A carpel is made up of a stigma, style and ovary. If there is one carpel, it can also be called a pistil. However, a pistil, the basic floral female reproductive structure may be composed of many carpels together. A flower can have many pistils as well. All the female parts of a flower together are called the gynoecium. So, from simplest to most complex: carpel > pistil > gynoecium.

Parts of the carpel:

* Stigma: This is outermost area of the female reproductive structure, located at the end of the stalk-like style. The stigma is the place where the pollen grains must first come in contact with the female part of the plant in order to pollinate and fertilize the flower. This structure is covered in a sticky substance that the pollen grains can adhere to.

* Style: The stalk between the stigma and the ovary.

* Ovary: This is the innermost female reproductive structure; a protective chamber housing the ovules. After fertilization takes place, the ovary develops into the fruit.

* Fruits: The fruit that we buy in the grocery store (and some of the things that we consider vegetables, but which are actually fruits, such as tomatoes) were once a flower's ovary. After fertilization, the ovary developed into a fruit and the tiny ovules into seeds. Fruits are expensive for a plant to produce, but their purpose is to entice animals to disperse the plant's seeds. The animal eats the fruit, moves along, and then drops the seeds in a new location when it poops.

*Nectar: The Sweet Stuff*

The nectary is where the sugary nectar is produced and held. Nectar is made to entice pollinators into the flower. Look carefully at a showy blossom and you will see how a would-be pollinator would need to brush by the reproductive parts in order to access this sweet treat inside the flower.

*Sources*

Campbell, Neil A. and Reece Jane B (2001). Biology, 6th edition. Benjamin Cummings.

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