Morphology of Flowering plants

Flower

Flowers are no doubt the most enticing parts of plants. You hardly even look at the plants who do not have flowers! Isn’t it? However, more than the aesthetic pleasure, the flower performs other important functions. Ever wondered if flower bouquet didn’t exist. Yes! Flowers are so much more than the beautiful and colorful petals and fragrance. Here, we will study flowers in more detail. We will cover all of the various parts of flowers as well. But, before we proceed, do you know what flowers actually are?

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What are Flowers?

Flowers are the reproductive unit in the angiosperms. These are the main parts responsible for sexual reproduction in these plants. In simple terms, without flowers, these angiosperms won’t be able to produce more like themselves! A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle.

These four parts are called calyx, corolla, androecium, and gynoecium. Calyx and corolla are accessory organs. On the other hand, androecium and gynoecium are reproductive organs. However, there are some exceptions to this.

Perianth

In some flowers like lily, the calyx and corolla are not distinct and are termed as perianth. Now, we will look at the various parts of flowers in greater details.

flower bouquet

Parts of the Flower

Each flower normally has four floral whorls, viz., calyx, corolla, androecium, and gynoecium. Let us look at each of these parts individually.

i) Calyx (Sepals)

The calyx may be gamosepalous (sepals united) or polysepalous (sepals free). Generally, sepals are green, leaf-like and protect the flower in the bud stage. They form the outermost whorl of the flower.

ii) Corolla (Petals)

Petals are usually brightly coloured to attract insects for pollination. Yes! That is why the flowers are coloured and attractive! Corolla may be also free (gamopetalous) or united (polypetalous). The shape and colour of corolla vary greatly in plants. It may be tubular, bell-shaped, funnel-shaped or wheel-shaped.

iii) Androecium (Stamens)

This part of the flower represents the male reproductive organ. Each stamen consists of a stalk or a filament and an anther. Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in pollen-sacs. A staminode is a sterile stamen.

When stamens are attached to the petals, they are called epipetalous. The examples of this type include brinjal. When stamens are attached to the perianth, they are called epiphyllous. Lily is an example of this type. Flowers are also classified on the basis of the fusion of stamen. They are divided into the following types.

  • Polyandrous: In this, the stamens in a flower remain free.
  • Monadelphous: In these, the stamens are united into one bundle. Examples include China rose.
  • Diadelphous: These have the stamens united into two bundles. Examples include pea.
  •  Polyadelphous: In Polyadelphous, the stamens are united into more than two bundles. Examples include citrus. There may be a variation in the length of filaments within a flower, as in Salvia and mustard.

iv) Gynoecium (Carpels/Pistils)

The gynoecium is the female reproductive part of the flower. It consists of three parts – stigma, style, and ovary. An ovary is the enlarged basal part, on which lies the elongated tube, the style. The style connects the ovary to the stigma. The stigma is usually at the tip of the style and is the receptive surface for pollen grains.

Each ovary bears one or more ovules attached to a flattened, cushion-like placenta. We can classify gynoecium into further types:

  • Monocarpellary: These have only one carpel.
  • Multicarpellary: These have more than one carpel.
  • Apocarpous: When carpels are free. e.g., lotus and rose.
  • Syncarpous: When carpels are fused. e.g., mustard and tomato.

After fertilisation, the ovules develop into seeds and the ovary matures into a fruit.

Aestivation

Aestivation is the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl. We have mentioned the various possibilities below.

  • Valvate: When sepals or petals in a whorl just touch one another at the margin, without overlapping. e.g., Calotropis.
  • Twisted: If one margin of the appendage overlaps that of the next one and so on. e.g., China rose, lady’s finger and cotton.
  • Imbricate: If the margins of sepals or petals overlap one another but not in any particular direction. e.g., Cassia and gulmohur.
  • Vexillary (papilionaceous): It’s a special type of aestivation. It has five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel). e.g., Pea, Bean.

 Solved Examples for You

Q: Mention the different types of flowers.

Solution:  There are different types of flowers based on their reproductive organs, symmetry etc.

  • On the basis of reproductive organs, flowers are unisexual or bisexual.
  • On the basis of symmetry, flowers are Actinomorphic (radial symmetry), zygomorphic (bilateral symmetry) or asymmetric (irregular).
  • A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5, respectively.
  • On the basis of bracts, flowers can be Bracteate and Ebracteate.
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