The Parts Of A Flower

You may not put any thought into a flower’s function past its visual appeal, and what it might look like in your garden.

The vast majority of flowers are not there to look pretty to us, however.

Their main design is to attract pollinators, to transfer pollen from the flower to another, ensuring that the plant’s genetic code is carried on well after the plant dies.

Attractive shapes, bright colors and markings all help the flower to be seen amongst the rest.

Patterns and forms of the bloom can act as a signpost to insects and birds, telling them exactly where the nectar is.

Some flowers have very specific pollinators, and have evolved to stop others from taking their precious nectar.

Interested in learning more? Here’s what you need to know.

What Is A Pollen Vector?

In terms of plants, a vector is something that picks up pollen from a flower and transfers it to another.

While your first thought might be a bee, yes, that’s true, but it’s by far only scratching the surface of what a vector can be.

Vectors can be any insects that transfer pollen, or birds, for example, such as hummingbirds, humans (either by accident or on purpose), or even things that aren’t living, such as the wind or the rain.

But their job doesn’t stop there. Once plants have formed seeds, these vectors also help scatter them through the environment, to form new plants.

You may notice that some seed pods only open when they are blown by the wind, and these tiny seeds are then dispersed away from the parent plant.

Maybe you’ve noticed birds or other animals eating seed heads or seed pods. Even that plays a role, as their droppings also carry the seeds into a new home, each one potentially a new plant.

Vectors can be divided further into two categories: Biotic Vectors, which are living things, and Abiotic Vectors, which are not.

The next time you’re in your garden or in a park when things are in bloom, have a look at the flowers which are being visited by pollinators.

You may notice that they’re fancier, more brightly colored than those which are pollinated by the wind or water.

The Anatomy Of A Flower

Four Key Parts You Should Know

Sepal

Sepals are the part of the flower that emerges first, where the flower is going to open, acting as the bud to begin with.

These outer parts protect the softer sections such as the petals and the organs as the flower starts to open out, and they also stop the flower from drying out before it manages to open and be pollinated.

Sepals are technically leaves, and usually appear green as a result, but they can come in nearly any color you can think of.

Not all plants form sepals, but some flowers feature modified sepals which are colorful bracts, surrounding a much smaller, true flower.

Petals

Petals are the part which help draw the pollinators to the plant, which is why they are typically the brightest, most dramatic part of the flower.

They are often shaped like a cup, or an umbrella, and are made up of many layers of tissue. In the case of flowers that open when the sun is out, closing when it goes in, the petals help the plant to retain moisture (see also Why Do Flowers Close Up At Night?).

Stamens

The stamen is the male reproductive organ within the flower, and it’s made up of two parts, the filament, and the anther.

The filament is a long tendril, sometimes curving inward or outward. It acts as a support for the anther, allowing pollinators easy reach.

The anther is a sac, which is where the pollen comes from. An anther is capable of holding large amounts of pollen.

When a pollinator touches the anther, the pollen attaches itself to them, and when the pollinator visits another flower, this pollen transfers with the help of a carpel.

Carpel

The carpel, otherwise known as the pistil, is the female reproductive organ.

Carpels tend to look a bit like a bowling pin, and sit in the center of the flower. In the middle, the carpel contains the ovary, forming unfertilized seeds inside this sac.

When they have fertilized, the ovary then turns into fruit.

Other Parts Worth Mentioning

Only two of the above, the carpel, and the stamen, are involved in reproduction, as the section above is the most basic form of the flower.

Let’s look at other parts you should know.

Bracts

Bracts are modified leaves, similar to sepals. They form before the flowers, usually a completely different color and shape from the leaves.

These tend to form on plants which don’t have any sepals, and protect the flowers.

Passionflowers, for instance, have bracts which smell rather bad, which stops any grazing animals from wanting to nibble on the flowers.

Corolla

The corolla is the part of the flower which makes up the petals, whether they are fused together or separate, often forming a ring.

Stigma

The stigma is the tip of a carpel, typically found in the middle of the flower, and it’s designed to receive pollen from other plants. It might be very long, curved, or feathery.

Style

The style of the flower is the long part of the carpel. This serves to transport pollen into the ovary from the stigma.

Receptacle

This part is the bit between the stalk and the flower, helping to support the weight of the bloom, or even fruit.

Perianth

The perianth collectively refers to the parts of the bloom which surround the organs.

You have an inner perianth, which is the corolla.

The outer perianth of the flower is the calyx, the group of sepals which form before the bud begins to open, protecting it from pests and moisture loss.

Tepal

A tepal is part of a perianth, and you can’t tell whether it’s a sepal or a petal, as each looks the same on the plant. You’ll most likely hear this term when looking at Irises.

Something To Keep In Mind

It’s worth knowing that some flowers are not limited to one type of each organ per plant. The Nigella flower, or Love-In-A-Mist, is the perfect example.

This enigmatic flower shows off a number of stamens as well as stigmas, only adding to the unusual shape and appearance of the flower.

Different Ways Of Classing Flowers By Their Reproductive Parts

As you probably know, there are many ways of classifying plants, from their appearance, their genetics, to their species.

Another thing that can set flowers apart is their reproductive parts. Not all flowers have the same parts, depending on the species, the flower’s function and what pollinates it.

Broadly speaking, there are two types of flowers. Complete flowers, and incomplete flowers.

But what are those?

What’s The Difference Between A Complete Flower And An Incomplete Flower?

While flowers widely vary in appearance, most of them are made up of the same parts.

There are four parts, typically: the petals, the sepals, the stamen, and the carpel (or pistil).

If a single bloom has all of these, it’s called a complete flower. If not, it’s called incomplete.

Complete flowers include roses, tulips, and lilies, as they have all four parts. Incomplete flowers include most types of grass flowers, squash, corn, and holly flowers.

Perfect vs Imperfect

In order to produce seed, flowers need a carpel, which is the female organ, and a stamen, which is the male organ.

If a single flower has both, this is called a perfect flower, regardless of whether it lacks any other parts, which would make it an incomplete flower.

If a single flower has only one of these two organs, it’s called an imperfect flower.

Perfect flowers include cherry blossom, carrot flowers, apple blossom, and orchids. Imperfect flowers include begonias, squash, and walnut blossoms.

Monoecious vs Dioecious: What’s The Difference?

Plants which produce imperfect flowers can be divided further into two types.

While the terms monoecious and dioecious look difficult, they couldn’t be simpler.

Monoecious plants produce male and female flowers on the same plant, as a single flower doesn’t have both organs needed for reproduction.

Some flowers will have carpel, and not stamen, and others will feature stamen and not carpel.

Because the flowers are on the same plant and in such proximity to each other, this allows the plant to self-pollinate, able to produce both fruit and seeds.

These plants are also called bisexual plants, as they have both male and female parts, even if they feature on opposite sides of the plant.

Dioecious plants don’t have this luxury. Dioecious plants produce only one gender per plant, either male flowers, or only female flowers.

These are called unisexual plants.

You’ll see them sold with very clear labels, either male or female plant, depending on which they produce, and you need to have both a male and a female plant near each other for pollination to happen.

Maize, squash, banana, and pumpkin plants are examples of monoecious plants, which produce both male and female flowers on the same plant.

Dioecious plants include junipers, spinach, mulberry, holly, and the ginkgo tree.

How Does Pollination In Flowers Work When They Have Male And Female Organs?

While we know that pollinators can visit one flower, and then another to pollinate the second flower, what happens when a flower has both organs it needs already, and there aren’t any other flowers around of the same type?

A rose is both perfect and complete. This means that it has all four main components to make it complete, and it also has both gendered organs, male and female, to make it perfect.

This means that it has everything it requires, apart from a vector. A pollinator must visit this flower in order for anything to happen.

An insect such as a bee or a butterfly, maybe even a bird lands on the flower, attracted to its appearance, which is essentially a sign saying “Find nectar here!”

Once they land, they will make contact with the anther to get at the nectar.

This transfers the tiniest of pollen from the male organs to the female organs, and the flower is pollinated.

While this isn’t a difficult method of pollination, it means that the seeds produced won’t have any diversity – they will look and act very similar to the parent plant.

This can be both a blessing and a curse. For one thing, the new plant will carry on the traits that have worked in the past to ensure the survival of the species, but it leaves it vulnerable to disease in the future, if diseases it is susceptible to evolve, and the plant (in new generations) does not.

Flowers And Nectar

Nectar comes from nectaries, which are tiny glands.

It’s important to note that the nectaries don’t actually produce the nectar themselves; instead, they secrete enzymes that break down the sugars into simple sugars, before releasing them into the nectar.

When the sun hits the flowers, it heats up the nectary, causing it to release nectar.

So, how do bees and other pollinators know where to go when they want to find nectar?

You may notice different colored markings in the middle of flowers, which help point the way to the nectar within the flowers, so pollinators know where to find the nectar.

Surprisingly (!), these are called nectar guides, acting as a landing strip as well as an inviting sign to these tasty treats.

Some flowers will produce nectar guides that we cannot see just with our eyes. After all, they’re not designed for us!

We can see them, however, under UV light, where they are incredibly clear.

They work by reflecting light back towards the insects’ eyes, making it easier for them to locate the source of the nectar.

In some cases, the nectar guide has other uses, too. The guide can be used as camouflage, helping to protect the plant from predators.

In fact, some plants use their nectar guides to attract beneficial insects, such as ants, who will eat aphids and other pests, ensuring that the plant survives long enough to reproduce.

Asexual Reproduction

You might know that sexual reproduction is not the only way a plant can reproduce itself. It can also reproduce through its roots, rhizomes, tubers, bulbs, and corms, or runners.

These parts of the plant are known as asexual reproduction because they don’t involve the reproductive organs stored in the flowers. 

Asexual reproduction results in plants that are essentially clones of the plant that has produced them. This can happen naturally, or you can make it happen by propagating, usually through grafting or taking cuttings.

Depending on the plant, cuttings can be taken as part of the stem, or the leaves. Cuttings are not a method that will work 100% of the time, so always take several cuttings at once to maximize your chances of some of the cuttings rooting into new plants. 

What About Wind Pollination?

Wind pollination, sometimes known as anemophily, is an interesting one. In this case, the wind is the pollinator instead of bees, butterflies, other insects or birds.

Wind pollination, as mentioned earlier, is an abiotic vector. The wind knocks the pollen out of one flower, and carries it to another.

The pollen is stored in the anther, the same as it is in normal pollination. In flowers that need wind to pollinate them, you’ll notice that the filaments are long and move easily with the wind.

The anthers tend to be much bigger and thinner than those in flowers which reproduce sexually. 

These anthers dangle delicately from the filaments, allowing the pollen to be carried away easily.

The stigma is also wider, allowing for a bigger surface area in which to catch incoming pollen.

There are also other differences in wind pollinated flowers, when compared to those which reproduce sexually. For one, they have no nectar, as they don’t need pollinators to visit the flowers.

Another distinct trait is that they don’t have a scent, which also acts as a beacon for pollinators.

For the same reason, the plant won’t produce showy or dramatic flowers, as they don’t need to compete with other flowers for insects to visit them.

Wind pollinated flowers need to produce significantly larger amounts of pollen than flowers which are pollinated normally.

This is to improve chances of the pollen flying into the right plant, and you’ll also notice that pollen from these flowers is so much smaller.

Final Thoughts

Flowers are beautiful no matter which ones you prefer, but the closer you look, the more you’ll realize that they’re an integral part of a very sophisticated ecosystem.

The flowers you choose to introduce into your garden can have a huge impact on your garden’s health.

If you decide right, by selecting a good amount of flower species which are native to your area, as well as the more ornamental plants, you’ll help support your local wildlife, which also bolsters the health of your garden, and the plants that live within it.

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