Aestivation: The Floral Arrangement

Aestivation, in botanical terms, describes the placement of the petals and sepals inside the flower bud before the flower blooms. It is often confused with vernation, which is the arrangement of scales and new leaves in a leaf bud before it opens. The sepals and petals are collectively known as a perianth. Botanists study aestivation to classify plant species, trace evolutionary relationships among the plants, and assist in identification. So, the term itself remains of extreme importance in biology, botanical studies, horticulture, and agriculture. This article discusses the meaning, types and examples of aestivation in plants for the Class 11 Biology exam, especially when practicing the chapter Morphology of Flowering Plants.

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What is Aestivation?

Aestivation definition in botany is the arrangement that petals and sepals are assigned to and held in before the opening of a flower bud. The said arrangement before opening is most of the time of huge importance about the developments received by the flower and the performance of its function. Botanists use it to identify and classify the 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. Patterns of aestivation affect the reproductive success of 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 numerous 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

• Valvate aestivation, the edges of petals or sepals, are seen to barely touch each other, showing no overlapping.

• It is the least differentiated and most simple type in which the floral parts remain plaits 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:

• In 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

• Vexillary aestivation 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: Exhibits quincuncial overlap for the protection of reproductive parts.
• Solanaceae Family: Frequently seen in flowers such as Datura and Solanum.

Read More:

• MCQ Practice on Aestivation
• Morphology of Flowering Plants
• Parts of Plants
• Anatomy of Flowering Plants

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 popularise easy penetration of the pollen or other parts of the flower by the vectors of the pollens 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 Different Plant Families

Aestivation patterns vary dramatically in different plant families, and each family presents unique characteristics.

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.

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

Examples

• Mustard, Brassica, Cabbage, Brassica oleracea.

Read More:

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