Aestivation: The Floral Arrangement

What is Aestivation?

The definition of aestivation in botany, the arrangement in which petals and sepals are assigned and held in before the opening of a flower bud. The said arrangement is of huge importance for the development of the flower and of its function. Botanists use it to identify and classify plant species into different categories.

The botanists will know flower aesthetics to understand the evolutionary interrelationships between different plant species. It also helps in the correct identification of plants, which becomes very important in botanical studies, horticulture, and agriculture. Aestivation affects the reproduction in plants through their effects on how flowers interact with pollinators and in protecting their reproductive organs.

Types of Aestivation

Aestivation in plants has been classified into several types based on the part arrangement of a flower bud. The commonly known types of aestivation are valvate, twisted, imbricate, and quincuncial aestivation.

Valvate Aestivation

• In this, the edges of petals or sepals barely touch each other, showing no overlapping.

• It is the least differentiated and simplest type in which the floral parts remain plaited along with each other.

Examples:

• Hibiscus and Family Malvaceae are some common examples belonging to the valvate aestivation category.

• This is a common pattern in members of the Malvaceae family.

Twisted Aestivation

• In this, the petals or sepals are overlapping each other, but in a methodical spiral manner.

• Each petal or sepal folds over the next one in a regular sequence, so that it overlaps in a one-way twist.

Examples:

• The Malvaceae, such as cotton and hibiscus, usually have twisted aestivation.

• China rose (Hibiscus rosa-sinensis) - is one of the common examples.

Imbricate Aestivation

• In this, the petals or sepals will overrun one another and result in irregular overlapping.

• There is no definite pattern of overlap, and the arrangement seems haphazard.

Examples:

• Cassia and Gulmohar (foliage: Delonix regia) belonging to the Fabaceae family exhibit imbricate aestivation.

• This kind is common in many plants belonging to the leguminous species.

Vexillary Aestivation

• It is a mixture of imbricate and valvate; in the sense, that there are both overlapping and touching margins.

• Generally, any two petals or sepals overlap, two are overlapped, and one portion is external.

Examples:

• Solanaceae family, such as Solanum and Datura.

• Aestivation also occurs in the family Brassicaceae.

Quincuncial Aestivation

• The five-petaled or five-sepal arrangement, with two entirely inside, two entirely outside, and one overlapping partially.

• Overlapping is very complex in a spiral fashion, covering the inner floral parts.

Examples:

• China Rose (Hibiscus rosa-sinensis), shows quincuncial overlap for the protection of reproductive parts.

• Solanaceae Family, frequently seen in flowers such as Datura and Solanum.

Table of Aestivation Types

Here is a table clearly showing the types of aestivation found in different kinds of flowers:

Biological Importance of Aestivation

Aestivation is of great importance in varied biological processes, mainly in the reproduction and evolution of plants.

Pollination factor:

• An appropriate type of aestivation may facilitate easy penetration of the pollen or other parts of the flower by the vectors of the pollen so that healthy pollination occurs.

• Specific aestivation type attracts specific kinds of pollen vectors. This results in species-specific pollination.

Protection of Reproductive Parts:

• It helps protect sensitive reproductive organs,stamen and pistils, from environmental stress and damage.

• Overlapping patterns may shade reproductive parts from too much sunlight, pests, and other harmful elements.

Aestivation in Plant Families

Aestivation patterns vary dramatically in different plant families, and each family presents unique characteristics. These patterns are not something random, they are consistently found within a family and helps in identifying and classifying the plants. Here are the variations of Aestivation found in different families of plants:

Fabaceae

• In Fabaceae, it shows imbricate aestivation.

• It shows overlapping of petals or sepals without a specific pattern.

• Examples- Cassia, Gulmohar (Delonix regia).

Solanaceae

• In Solanaceae, it is usually quincuncial aestivation.

• Combination of overlapping and touching edges.

• Examples- Solanum, Datura.

Brassicaceae

• Most of the species show quincuncial aestivation.

• The evolution of adaptive features of the floral structure to provide more protection and better pollination.

• Examples - Mustard, Brassica, Cabbage, Brassica oleracea.

Factors Affecting Aestivation

Aestivation is determined by genetics, evolution, and environment. Patterns of petal and sepal arrangement are regulated by certain genes. Evolution prefers those patterns that are advantageous in pollination and defense. Light and wind, which are environmental factors, also determine these patterns. Aestivation types in plant families tend to remain constant, assisting in their classification.

Aestivation NEET MCQs

Q1. In twisted aestivation

1. There is a regular overlapping of petals/sepals

2. There is an irregular overlapping of petals/sepals

3. There is no overlapping of petals/sepals

4. None of these

Correct answer: 1) There is a regular overlapping of petals/sepals

Explanation:

Aestivation is the position of sepals or petals in a floral bud. There are:

1. Valvate: Margins touch without overlapping (e.g., Calotropis).

2. Twisted: One margin overlaps the next (e.g., China Rose).

3. Imbricate: Margins overlapping irregularly. For example: Cassia.

4. Vexillary: The largest petal overlaps the wings and keel in pea flowers.

5. Quincuncial: Two petals inner, two outer, and one partly inner (e.g., Ranunculus).

Hence the correct answer is Option (1) There is a regular overlapping of petals/sepals.

Q2. Irregular overlapping occurs in

1. Twisted aestivation

2. Valvate aestivation

3. Imbricate aestivation

4. All of these

Correct answer: 3) Imbricate aestivation

Explanation:

Aestivation refers to the arrangement of sepals or petals in a floral bud in relation to other members of the same whorl. There are several types of aestivation in the corolla and calyx: Valvate aestivation occurs when sepals or petals in a whorl simply touch at the margins without overlapping, as seen in Calotropis; Twisted aestivation is when one margin of a petal overlaps the next, as seen in China Rose, Lady's finger, and cotton; Imbricate aestivation involves the overlapping of sepals or petals without any specific direction, seen in Cassia and Gulmohar; Vexillary aestivation is found in pea and bean flowers, where the largest petal (standard) overlaps the two lateral petals (wings), which in turn overlap the smallest petals (keel); and Quincuncial aestivation occurs when two petals are inner, two are outer, and one is partly inner and partly outer, as seen in Ranunculus.

Hence the correct answer is option (3) Imbricate aestivation.

Q3. Petals not overlapping each other are said to show

1. Twisted aestivation

2. Valvate aestivation

3. Vexillary aestivation

4. Quincuncial aestivation

Correct answer: 2) Valvate aestivation

Explanation:

1. Valvate Aestivation: When sepals and petals in a whorl just touch one another at the margin, without overlapping, as seen in Calotropis, it is called valvate aestivation.

2. Twisted Aestivation: If one margin of the appendage overlaps that of the next one and so on as seen in China Rose, Lady’s finger and cotton, it is called twisted.

3. Imbricate Aestivation: If the margins of sepals or petals overlap one another but not in any particular direction as in Cassia and Gulmohar, the aestivation is called imbricate.

4. Vexillary Aestivation: In pea and bean flowers, there are five petals. The largest (standard) overlaps the two lateral petals (wings) which in turn overlap the smallest anterior petals (keel). This type of aestivation is called vexillary and the corolla is called papilionaceous.

5. Quincuncial Aestivation: When two petals are inner and two outer and one is partly inner and partly outer, it is called quincuncial. For example, Ranunculus.

When sepals and petals in a whorl just touch one another at the margin, without overlapping, as seen in Calotropis, it is called valvate aestivation.

Hence the correct answer is Option (2) Valvate aestivation.

Read More:

• MCQs on Aestivation

• Aerial Stem Modification

• Types of Leaves

FAQs on Aestivation

What is aestivation in plants?

Aestivation in plants refers to the arrangement of sepals and petals (floral parts) within the flower bud before it opens. It describes how these floral structures overlap, touch, or remain free in the bud condition. Aestivation is an important morphological feature studied in botany for classification. Different plant families exhibit characteristic patterns of aestivation, which help botanists identify and differentiate between species.

What are the types of aestivation?

The main types of aestivation are:

• Valvate: Sepals or petals just touch each other without overlapping. e.g., Calotropis

• Twisted: Each petal or sepal overlaps the next one in a regular sequence. e.g., China rose

• Imbricate: Overlapping occurs, but not in a regular order. e.g., Cassia, Gulmohar

• Vexillary (Papilionaceous): A special type found in the pea family, the large standard petal overlaps two wing petals, which in turn overlap two smallest keel petals.
  
  

What is the difference between aestivation and vernation?

The key difference lies in the plant organ involved. Aestivation refers to the arrangement of floral parts (sepals and petals) inside the flower bud, while vernation (or prefoliation) refers to the arrangement of leaves within a vegetative bud. For example, twisted aestivation is seen in Hibiscus flowers, while convolute vernation is seen in banana leaves. Thus, aestivation is a floral feature, whereas vernation is a vegetative feature.

What is the importance of aestivation in biology?

Aestivation has great importance in plant taxonomy and identification. Many plant families can be recognized by their characteristic type of aestivation, such as vexillary aestivation in the Fabaceae (pea) family. It also provides insights into evolutionary adaptations of flowers to pollination. By studying aestivation, botanists can classify plants more accurately and understand structural diversity in flowers. Therefore, it is both a diagnostic and evolutionary feature in biology.

Recommended Video on "Aestivation"