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Morphology of Flower – Definition, Structure, Parts, Examples

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  • Last Updated : 27 Jun, 2022

The flower is the reproductive segment of angiosperms plants. It is an organ for sexual reproduction. A normal flower contains 4 different types of whorls. These whorls are organized consecutively on the bulged end of the pedicle (stalk) known as the receptacle (also known as the thalamus). Whorls of a flower are –

  • Calyx
  • Corolla 
  • Androecium
  • Gynoecium

The calyx and corolla are considered accessory organs of a flower whereas androecium, and gynoecium are considered reproductive organs of a flower. If the calyx and corolla are not noticeable, then it is termed perianth. This condition can be seen in lily. If a flower contains both reproductive organs of a flower that is androecium and gynoecium then it is termed a bisexual flower. If a flower contains either only androecium or only gynoecium then it is termed as unisexual.

Symmetry

Symmetry

 

Actinomorphic: If a flower can be bisected radially into 2 equal halves by passing in any radial plane by moving across the center, then it is known as an actinomorphic flower, e.g., Datura, chili.

Zygomorphic: If a flower can be bisected into 2 equal halves in 1 vertical plane then it is known as a zygomorphic flower, e.g., Bean, Cassia.

Asymmetric: If a flower cannot be bisected into 2 equal halves in a vertical plane at any angle by moving across the center, eg: canna.

Bract resembles leaves and these are located at the base of the pedicle. If the Flowers are with bracts, then they are called bracteate and  If they are without bracts, ebracteate flowers.

Depending on the organization and location of the calyx, corolla, and androecium with reference to the ovary over the thalamus, the flowers are categorized as hypogynous flowers, perigynous flowers, and epigynous flowers.

 

Hypogynous flower: In this flower gynoecium is situated at the higher position and the remaining parts are positioned below it. This type of ovary is considered as superior, e.g., Mustard, china rose.

Perigynous flower: In this flower gynoecium is located in the center and the remaining parts of the flower are positioned on the thalamus rim more or less at the same position. Here the ovary is considered as half inferior, e.g., Peach, Plum, rose.

Epigynous flower: In this flower, the thalamus margin grows upward surrounding the ovary totally, and getting merged with it, the remaining floral parts arise over the ovary. Thus, the ovary is considered inferior eg-Sunflower ray florets,  flowers of guava, and cucumber.

Parts of a Flower 

A flower has 4 whorls calyx, corolla, androecium, and gynoecium.

Calyx 
The calyx is the external most whorl of the flower. A group of sepals collectively forms calyx. Normally, sepals are green and resemble leaves. They enclose and protect the flower in its budding stage. If sepals are fused with each other, then the calyx is gamosepalous. If sepals are not fused with each other and free, then the calyx is polysepalous.

Corolla 
Corolla contains petals. The bright color of these petals attracts insects for pollination. If petals are united then the corolla is said to be gamopetalous and if petals are free then the corolla is said to be polypetalous. The structure and color of corolla differ significantly in plants. The shape of the Corolla may be wheel-like, bell-shaped, tubular, or funnel-shaped.

Aestivation

The manner in which sepals or petals are organized in a floral bud with reference to other parts of the same whorl is called aestivation.

Aestivaation

 

Valvate aestivation- In a whorl, if petals or sepals just touch each other at the ends i.e margin but do not overlap each other then this type of aestivation is termed as valvate. Example: Calotropis

Twisted aestivation- If one end of sepals or petals  overlaps with the other appendage then it is termed twisted aestivation Examples: Cotton and china rose

Imbricate aestivation- If the ends of sepals or petals overlap each other but not in any specific direction then the aestivation is termed Imbricate aestivation. Example: Gulmohur and Cassia species

Vexillary aestivationSuppose for example in the flowers of a bean plant, there are 5 petals, of them, the largest in the standard petals. This standard petal overlaps the other 2 lateral petals, these lateral petals are termed wings. These wing petals again overlap the other two smallest anterior petals. These anterior petals are termed the keel. This type of aestivation is known as vexillary or papilionaceous.

Androecium 

Androecium

 

Androecium contains stamens. The stamen is the male reproductive organ of a flower. It contains a filament and an anther. In general, the anther contains 2 lobes (bilobed) and every lobe contains  2  chambers. These are called pollen-sacs. Pollen grains are produced inside these pollen sacs.

If a stamen is sterile, then it is known as staminode. These Stamens of a flower may get fused with other parts like petals or may get fused among themselves.

  • If stamens adhere to the petals, Then the condition is known as epipetalous Example:  brinjal.
  • If they adhere to perianth, then the condition is known as epiphyllous. Example: flowers of lily.

If the stamens in a flower are free and don’t adhere to each other, then they are said to be polyandrous.

The stamens may fuse to different degrees. If they fuse with each other and form into a single bunch or single bundle, then the condition is known as a monadelphous condition. Example:  china rose, or If they fuse to form two bundles, then the condition is known as diadelphous. Example:  pea, or  If they fuse to form more than two bundles then the condition is polyadelphous condition Example: citrus.

Gynoecium 

Gynoecium

 

Gynoecium represents the female reproductive organ flower, and it contains one or many carpels. It contains three parts, they are stigma, style, and ovary.

The ovary bugles the basal part of the carpel, the style is present on this carpel. The style links stigma and ovary. The stigma is generally situated at the end of the style and is the receiving surface for pollen grains during the process of pollination. An ovary contains one or many ovules adhered to a flattened, cushion-like structure known as the placenta.

If there is more than 1 carpel, and they are free, then the condition is called apocarpous condition. If there is more than 1 carpel, and they are fused, then this condition is known as a syncarpous condition. After the process of fertilization, the ovules evolve into seeds and the ovary develops into a fruit.

Conceptual Questions

Question 1: What are aestivation and name different types of aestivation?

Answer:

Aestivation: The manner in which sepals or petals are organized in a floral bud with reference to other parts of the same whorl is called aestivation. The major types of aestivation are valvate aestivation, twisted aestivation, imbricate aestivation and vexillary aestivation.

Question 2: What are placentation and name different types of placentation?

Answer:

Placentation: The organization of ovules inside the ovary is known as placentation. There are different types of placentation like marginal placentation, axile placentation, parietal placentation, basal placentation, and free central placentation.

Question3:Mention different types of placentation with examples in tabulated form?

Answer:

Placentation Morphology  Example
Marginal 

It contains a ridge  formed by the placenta towards the ovary ventral suture  with 2 rows 

of ovules 

Pea
Axile Here placenta is in axial  position .The ovary is multilocular and adhered to placenta. China rose ,Lemon
Parietal

Ovules are born towards the periphery or formed inner side  of the ovary wall.

Ovary appears as 2 chambered due to formation of false septum

Argemone
Basal Placenta is formed from the bottom of the ovary with one ovule Marigold
Free central Septa are absent. Ovules are adhered to central axis Primrose

 

Question 4: Write examples of different types of symmetry in flowers?

Answer : 

  • Actinomorphic : Datura, chilli.
  • Zygomorphic : Bean,Cassia.
  • Asymmetric :   canna.

Question 5: Write examples of  Hypogynous, perigynous and epigynous flowers?

Answer : 

Depending  on calyx, corolla and androecium position  with respect to the ovary over thalamus, the flowers are classified  as hypogynous flowers , perigynous flowers and epigynous flowers.

  • Hypogynous flower  :  Brinjal, mustard, china rose.
  • Perigynous flower :  Peach, plum, rose.
  • Epigynous flower : Sunflower ray florets,  flowers of guava and cucumber
     

Question 6: What are epipetalous and epiphyllous conditions?

Answer : 

  • If stamens and petals are adhered with each other Then the condition is known as epipetalous Example:  brinjal.
  • If stamens and perianth  are adhered to one another then the condition is known as epiphyllous. Example: flowers of lily.

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