Aestivation: Definition, Types, and Examples for Class 11th and NEET

Define: Aestivation

  ‘Aestivation” refers to the arrangement of petals and sepals in the bud. Valvate, Twisted, Imbricate, and Quincontial are several kinds of aestivation.

1. Valvate: Mustard, Annona, and Mimosa are examples of Valvate flowers, which have sepals and petals that do not overlap.

2. Twisted (Contorted) Aestivation has one margin in and one margin out for each Sepal and Petal. (One sepal or petal’s margin overlaps the margin of the next.) Hibiscus with cotton, for example.

3. Imbricate: The petals and sepals are arranged in such a way that one petal or sepal shows both margins in, one petal or sepal shows both margins out, and the remainder of the petals and sepals show one margin in and another margin out.

 In ascendingly imbricate aestivation, overlapping begins on the anterior side and progresses to the posterior petal. Cassia, Caesalpinia, etc.

The overlap in the descending aestivation imbricate begins at the back, with the front petal being the innermost.’Vexillary aestivation’ is another name for it. Pea, Banana, and Crotalaria are just a few examples.


The calyx is the flower’s outermost protective accessory whorl. It has a green hue to it. It’s sometimes termed a ‘Petaloid sepal’ because it’s brilliantly colored.

Flower showing Calyx

1. Polypetalous: refers to a flower with free petals, such as a rose.

2. Gamosepalous: It’s called ‘Gamosepalous’ when Sepals are fused. Hibiscus, for example.

3. Caducous: refers to a flower that sheds its sepals as soon as it opens.

4. Deciduous: It’s called ‘Deciduous’ if the sepals last as long as the petals.


The second accessory whorl of a flower made up of Petals is the Corolla. It’s a colorful, fragrant, and appealing whorl. Polypetalous refers to a flower with free petals. Hibiscus, for example. It’s called Gamopetalous when Petals are fused. Jasmine.


The function of Corolla:-

1. The role of the corolla is to safeguard the flower’s vital whorl.

2. Insects are attracted to it for cross-pollination.

Forms of Corolla.

Corolla comes in a variety of shapes and sizes depending on the shape and fusion of its petals.

1. Cruciform: The Cruciform kind of Corolla has four free clawed petals arranged in a cross shape. Mustard and radish are two examples.

 2. Papilionaceous: The Papilionatae Family has these traits. The corolla in this kind has five unequal petals. The posterior one petal is large and known as the ‘Standard petal,’ two lateral petals are known as the ‘Wing petal or Alae,’ and the anterior two petals are joined along one margin to form boat-shaped structures known as the ‘Keel petal’ or ‘Carina.’ It contains the Essential whorls.

3. Companulate: The form of a bell.

4. Tubular: In this type, the petals are joined together to form a complete tube. Florets of the Asteraceae family, for example.

5. Bilabiate: Two lips-like structures formed by fusing the corolla. Example Leucas (Tumbae).

6. Infundibulum: A funnel-like structure formed by the terminal segments of the petals progressively expanding out from the corolla. Example Ipomoea, Datura


The androecium is the male reproductive organ of a flower’s third whorl. It is made up of stamens. Each Stamen is made up of a long, slender Filament (stalk) and two Anther lobes that are joined by Connective. In Tetrasporangiate anthers, each lobe has two chambers called Microsporangia, and one microsporangium in eusporangiate anthers. Following variations can also be noticed in stamens.


Anther to filament attachment:

1. Basifixed: The filament is attached to the Anther’s base. Mustard and radish are two examples.

2. Dorsifixed: The filament is secured to the rear of the Anther. Passiflora, for example.

3. Adnate: Throughout its length, the filament is connected to the Anther. Michelia, for example.

4. Versatile: Anther’s attachment is in the middle, allowing both ends of Anther to swing freely in the air. Grass, for example.

5. Introrse: An anther dehisces towards the flower’s center.

6. Extrorse: Anther dehiscing towards the flower’s periphery.

7. Dithecous has two-lobed anthers.

8. Monothecous: A single lobed anther.

II. Stamens’ Union:

Filaments, Anthers, or both Anther and filaments can connect stamens in a flower. As a result, they are given the following names:

1. Adelphous: Adelphous is a state in which all of the stamen filaments are united and the anthers are free in a flower.

 a) Monadelphous:  In this type, all of the stamens’ filaments are joined together to create a single bundle. Members of the Malvaceae family, for example (Hibiscus, Cotton).

b) Diadelphous: A flower’s components are joined to form two bundles. Beans and peas, for example.

c) Polyadelphous: Filaments are made up of numerous stamen bundles. Lemon is a good example.

2. Syngenesious: When the anthers of all the stamens are connected and the filaments are free in a flower, this is referred to as “Syngenesious.” Members of the Asteraceae family, for example. (The Sunflower)

3. Synandrous Stamens: When the filaments of all the stamens and filaments are linked in a flower, this is referred to as “Synandrous Stamens.” Members of the Cucurbitaceae family, for example. (Cucumis).

III. Stamen length

Stamens often reach varied lengths, resulting in the following conditions:

1. Didynamous: In a flower, if there are four stamens, two of which are long and two of which are short, the flower is said to be didynamous. For example, Oscimum and Leucas.

2. Tetrandynamous: A flower with six stamens, four of which are long and two of which are short.

Mustard and radish are two examples.

1. Gynandrous: Stamens partially or completely merged with carpels.

2. Obdiplostemnous: two whorls of stamens. Petals alternate with the outer whorl.


The gynoecium is the female reproductive organ and the innermost whorl of a flower. It is built up of ‘Carpels’ or ‘Megasporophylls,’ which are small units. The ‘Ovary,’ a swelling basal region, a filamentous style, and the ‘Stigma,’ a knob-like terminal section, make up each capel. Ovules are tiny, spherical structures found on the ovary.


1. Stigma can be capitate (like a globose head), feathery (with hairy growth), or bifurcated (with two stigmas).

2. Gynobasic refers to a style that emerges from the ovary’s base. Stylopodium is a round disc that surrounds the style’s base.

3. In an ovary, the number of carpels varies. The monocarpellary ovary contains one carpel, the Bicarpellory ovary contains two carpels, the Tricarpellory ovary contains three carpels, Tetracarpellory ovary contains four carpels, Penta carpellary ovary contains five carpels, and Polycarpellory ovary contains more than five carpels.

4. Carpels that are separated from one another are referred to as ‘Apocarpus ovary.’ Michelia, for example.

5. The locules are the cavities in the ovary that house the ovules. The number of locules is frequently used to predict the number of carpels. Unilocular ovary has one locule, bilocular ovary has two locules, trilocular ovary has three locules, and so on.

6. The placenta is the soft tissue that lines the inside of the ovary.

8. Ovules are connected to the ventral edge. Pea, for example.

9. Basal, with ovules connected to the ovary’s base e,g Sunflower

10. Parietal, containing ovules connected to the ovary’s inner walls e,g Cucumis

11. Gynophore: Gynophore is a stalk-bearing gynoecium.

12. Gynandrophore: A Gynandrophore is a stalk that contains both Androecium and Gynoecium. Gynostegium: Gynostegium is a sheath that covers the gynoecium and anthers.

Gynophore is a stalk-bearing gynoecium. Gynandrophore is a stalk that contains both Androecium and Gynoecium. Gynostegium is a sheath that covers the gynoecium and anthers.

Ovary Apocarp and Syncarp

The number of carpels in an ovary in the female reproductive organ of the flower gynoecium is varied. The monocarpellary ovary includes one carpel; the Polycarpellory ovary contains more than five carpels. Apocarpous ovary: When carpels are separated from one another, they are referred to as “Apocarpus ovary.” Michelia, Syncarpus ovary’, for example, Ladies finger is an example of syncarpus ovary, which occurs when carpels are joined.

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