Flowers

Flowers were an evolutionary development that allowed the plant kingdom to boom into the huge diversity of species that currently exist. They were developed as an alternative method of reproduction and proved to be very successful. Flowers are admired around the world for their beauty and fragrance but perform an important function that has enabled Angiosperms to become the dominant group of plants on Earth.

Flowers take advantage of the mobility of insects and other animals to serve as dispersers of pollen between plants. They are designed to lure insects and other animals in to feed on their nectar. In doing so, animals collect pollen on their head and body. If the animal then continues to feed on more flowers, it acts as a pollinator by carrying pollen from the flower to flower. If pollen is rubbed onto the correct part of a new flower, it may then be fertilized.

A flower is made up of a number of different parts that each play a role in the reproduction of plants. These include the petals, stamens, a carpel and an ovary.

Petals and sepals

The petals of the flower are modified leaves and serve as an advertisement of the plant to birds, insects and other animals to come and feed at the plant. They are often brightly colored to entice animals towards them.

Five petalled flowersThe number of petals on a flower varies largely across angiosperms and can be used to help identify a monocot plant from the eudicots and basal angiosperms. Monocots tend to have flowers with petals in multiples of three; whereas eudicots and basal angiosperms have flowers in fours or fives.

The amount of fusion between petals is useful in determining how evolutionarily advanced a plant species is. If the petals of a plant have a high level of fusion between them, they are likely to belong to a recently evolved lineage of plants. If, on the other hand, the petals show no level of fusion they are likely to belong to a more primitive group of plants. A lack of fusion between petals is common in basal angiosperms such as the magnolias.

Carpel

The carpel is the female reproductive part of the flower that receives pollen and facilitates the transport of plant sperm to the ovary. They carpel consists of the style and the stigma.

The style is an elongated structure that facilitates the transport of sperm to the ovary once pollen has landed on the stigma. The base of the style connects to the ovary and the tip of the style becomes the stigma. Along the length of the style runs tubes known as pollen tubes in which sperms are able to travel through.

The stigma is a widened head at the top of the style that provides a sticky surface for pollen to land on. After pollen has landed on the stigma, sperm is released and enters the pollen tubes before travelling down into the ovary.

Ovary

The ovary is the structure that houses the ovules and eggs of a plant. The eggs are located within the ovules and once they are fertilised they begin developing into seeds. As the eggs develop into seeds, the ovary becomes a fruit. In many plants the ovary develops into a fleshy, edible fruit. The ovaries of other plants develop into dry shells such as the shells of walnuts or acorns.

Stamen

StamenThe stamen is the male part of a flower. It includes the anther and the filament. The filament is the elongated structure that supports the anther on its tip. The anther is where pollen is produced and displayed for animals to collect while they are feeding at flowers. A single flower can have many stamens each with an anther that will be covered in pollen.

Pollen

Pollen is the substance that most plants use to reproduce. It contains the sperm of a plant and is built to withstand travelling long distances between flowers, often many hundreds of metres apart.

Pollen is generally lightweight and sticky. It easily rubs onto insects and other animals as they feed and again rubs off onto the stigma of another flower. Most flowers will produce millions of pollen grains but only a handful might need to reach another flower in order for reproduction to be successful.

Last edited: 21 May 2015

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