Flowering Principles

We will start our description of flower structure with perfect flowers. Perfect flowers are those that have special organs that, 1) make and distribute the male gametes, 2) make the female gamete, and 3) receive the male gamete.

The most visual component of the flower is the petal. From a human perspective, the motivation for growing a plant is often based on the attractiveness of the petals. Insects are also attracted to these flower petals and in nature, plants can benefit from visiting insects to move pollen within and between flowers. Sepals are the structure beneath the petals. Sepals can look like the petal but function as the protective layer around the unopened flower.

The petals. Image by UNL

The sepals. Image by UNL

Perfect flowers will have structures called stamens that produce the pollen (male gametes). A stamen consists of the anthers where the pollen is made and filaments which support the anther. Perfect flowers will also have the female reproductive structures called the pistil. The three main parts of the pistil are the stigma where pollen will land, the style where the pollen will grow and the ovary were eggs (female gametes) are made and the seed develops. An ovary may have several or many ovules. Each ovule has the female egg cell that combines with the pollen to form the seed embryo plus other cells that will develop into the seed endosperm and seed coat. The ovary is supported by the pedicel.

The stamen, anther and filament. Image by UNL

The pistil. Image by UNL

The ovule and the ovary. Image by UNL

View the Flower parts animation.
Complete the activity to see if you are learning the names of the flower parts, by clicking on the animation 'picture' link below.
(Flower Parts) Animation Link
Animation by UNL Why do we call flowers with functional male and female parts perfect? This is because the flower has everything needed to produce a seed by sexual reproduction. The anthers produce pollen and ovules develop in the ovary in the same flower. If ripe pollen lands on a receptive stigma, the pollen can grow a tube through the style and the pollen nucleus with all of the genetic information can travel through the tube and combine with the egg in the ovule. The ovary protects and nourishes the zygote and supports the development of the embryo, endosperm and seed coat of the seed.

Perfect flower with pollen on stigma. Image by Patricia Hain

Growing pollen tube. Image by UNL

Seed. Image by UNL

See how the flower parts work together to produce a seed.

Click on the animation 'picture' link below then click on 'Flower Structure'.
Animation Link
Animation by UNL
The parts of a perfect flower will stay the same but there are many versions of perfect flowers in the world. For example some perfect flowers have a structure that keeps the stamens separated from the pistil until an insect visits the flower. When a bee, for example, explores the flower for nector, specialized petals are tripped and out springs the stamen. This showers the insect with pollen, which it will carry to other flowers. So insects visiting these kinds of flowers promote cross pollination, the pollen from one plant landing on the stigma of another. Other perfect flowers promote self pollination where the anther efficiently sheds pollen onto the stamen as they mature at the same time. Some plants have perfect flowers but the pollen tube will not grow through the style from the same plant. These plants have self-incompatible flowers and must cross pollinate to produce seed.

Oat flowers self pollinate because of their perfect structure. Image by Don Lee	Can you spot the pollinator? Image by Don Lee	Lily flowers are perfect but insect visits can promote cross pollination. Image by Don Lee