Parts of a Flower and Their Functions

About ninety percent of all plants on the planet make flowers. Some are showy, colorful, and striking, while others are so subtle and miniscule that people don’t even notice them. They’re a botanical feature that is over 120 million years old and has been of great benefit to the plants that make them.

And, while they’re extremely diverse in appearance, flowers all throughout the plant kingdom are composed of the same basic physiology. They all have the same basic parts, albeit some have developed them in extremely unique ways. In this text, we will dive into all the basic parts of a flower and the functions they play in plant biology.

What Is A Flower and What Are Its Parts?

Flowers are the reproductive structures of plants. Their primary function is to produce seeds and ensure healthy genetic exchanges between individuals in a population. To do this, many of them have developed striking colours, odours, and forms to attract a diverse array of pollinators.

The primary parts of a flower can be divided into two distinct groups. These are the reproductive parts and the non-reproductive parts of the flower. Depending on the plant family, the numbers and shapes of each of these parts may vary.

Non-Reproductive Parts Of A Flower

• Sepals (Calyx): Sepals are the outer layer of the flower that covers and protects the bud before the flower opens. Once open, the sepals remain at the bottom of the flower. Sepals are technically modified leaves and occasionally help attract pollinators. Monocots (grasses, orchids, palms, ect.) tend to produce sepals in pairs of 3, while dicots (roses, sunflowers, oaks, and most other plant species) produce them in pairs of 4 or 5. The calyx is the name used to describe all of the sepals in a flower.
  
  
• Petals (Corolla): We are all familiar with the showy petals found on flowers. They are technically modified leaves and sit between the sepals and the reproductive parts of a flower. In some cases, the petals may be conjoined to form tubes. Petals are crucial for attracting pollinators and often contain distinct features designed for specific pollinator species. For example, red flowers in tube shapes are typically used to attract hummingbirds. Some petals have UV markings invisible to the human eye that aid in attracting insect pollinators. The corolla is the name used to describe all of the petals in a flower.
  
• Receptacle: The receptacle is a bowl-shaped structure located at the base of the flower. All flower parts are directly connected to the receptacle.
  
  
• Peduncle: This is the stalk or stem that supports the flower and is connected to the receptacle. The peduncle may look nearly identical to the plant stem, but it may also have unique features, such as trichomes.
  
  
• Tepals: In some cases, plants produce tepals instead of sepals and petals. Tepals are when the sepals and petals are fused into a single structure.

Reproductive Parts Of A Flower

• Stamens: These are the male reproductive parts of the flower. They are composed of a long stalk called a filament that supports the pollen-containing anthers. The stamens are also referred to under the more technical term “androecium”.
  • Filaments are thin stalks that project from the center of the flower. In some cases, such as in the hibiscus family (malvaceae), they may be conjoined to form a “filament tube” that partially surrounds part of the pistils.
  • Anthers are often easy to see due to the brightly colored pollen that covers their surface. Pollen is often yellow in color but can be pink, purple, red, and many other colors. Under a microscope, pollen from different species have unique ornamentations and symmetry. Anthers are strategically placed to come in contact with pollinators, and some species vigorously release their pollen thanks to vibrations produced by pollinators.
    
    
• Pistils: These are the female reproductive parts of a flower. They contain the ovary, the style, and the stigma. The botanical term “gynoecium” is also used to describe the pistils
  • The ovary contains the female reproductive cells called ovules that turn into seeds following fertilization. The ovules are the gametes, or haploid cells, that contain 50% of the genetic information that will be passed down to the offspring.
  • The style is an elongated “stalk” that supports the stigma. It is centrally located and typically much sturdier than the filaments of a stamen.
  • The stigma is at the very top of the pistil and its job is to receive the pollen. It is often sticky and strategically placed to capture pollen from insect pollinators.

The Development Of A Flower

To further understand the parts of a flower, let’s take a look at the development of flowers and how they eventually produce seeds and become fruits.

1. Peduncle and Bud Formation

A flower first starts to develop through the elongation of the peduncle from a plant stem. This peduncle eventually forms an inflated and closed bud. Before opening up, this bud already contains all of the parts of the flowers within it. The very bottom of the bud is composed of the receptacle, while the rest of it is made of the leaf-like sepals.

2. Opening Of the Bud

When the bud opens, the flower unfurls, revealing all of the plant parts within. The sepals which cover the closed flower are going to be at the bottom of the flower after the bud opens. In some cases, one reproductive structure may develop before the other to reduce the risk of self-pollination. This is the case for many species in the laurel family (Lauraceae), such as Avocados. Self-pollination is not typically beneficial for plants because it does not provide any genetic diversity to their future offspring. Some plant species are completely incompatible with self-pollination due to genetic mechanisms they’ve developed to prevent it.

3. Pollination and Sexual Reproduction

The pistils and stamens always grow from the middle of the flower. While a large majority of plants rely on insect pollinators to transfer pollen from one flower to another, a handful of species are wind pollinated. Some wind-pollinated species include oak (Quercus), willow (Salix), and many different types of grasses (Poaceae). When a grain of pollen reaches the stigma, the pollen actually “germinates” and forms a structure known as the “pollen tube” that grows into the style. This tube eventually reaches the ovary and releases its genetic material in order to fertilize the ovule.

4. Fruit and Seed Production

Once fertilized, the plant begins investing a large amount of its energy into the production of seeds and fruit. Some plants produce hundreds, or even thousands, of seeds from a single flower (ex., tobacco, tomatoes, strawberries, kiwis, etc.). Other plants focus their energy on the production of a few energy-rich seeds (ex. oaks, walnuts, and chestnuts). In botanical terms, a “fruit” isn’t solely restricted to the sweet, fleshy foods we are familiar with, but it includes a large variety of seed-bearing structures.

Conclusion

Flowers are extremely diverse structures that help with the reproductive success of plant species. Despite them being extremely diverse across the plant kingdom, they all share the same basic physiology and parts. For botanists or plant enthusiasts, studying the parts of a flower can not only be fascinating but also bring unique insights into plant biology, reproduction, and taxonomic order.