Aestivation refers to the arrangement of sepals or petals in a flower bud before it opens. It is an important characteristic that helps in identifying different types of flowers. There are different types of aestivation patterns, such as valvate, imbricate, twisted, vexillary, and contorted.

In the given options, option 'A' is the correct answer, which states that aestivation is the arrangement of accessary floral organs in relation to one another in bud condition. This means that aestivation describes how the sepals or petals are arranged with respect to each other while they are still in the bud stage.

Explanation of the correct answer:
Aestivation is mainly concerned with the arrangement of sepals or petals in relation to each other in a flower bud. This arrangement can be observed by looking at the bud from the outside. The different types of aestivation patterns are as follows:

1. Valvate aestivation: In this pattern, the sepals or petals in the bud are touching each other at the margins without overlapping. It is commonly found in plants belonging to the family Malvaceae.

2. Imbricate aestivation: In this pattern, the sepals or petals overlap each other in a spiral or whorled manner. It is further classified into two types - quincuncial and cochlear. Quincuncial imbrication is when there are five sepals or petals in the whorl, and two opposite sepals or petals are completely external, two opposite sepals or petals are completely internal, and one sepal or petal is partially internal and partially external. Cochlear imbrication is when there are four sepals or petals in the whorl, and one sepal or petal is completely external, two opposite sepals or petals are partially internal and partially external, and one sepal or petal is completely internal.

3. Twisted aestivation: In this pattern, the sepals or petals are twisted or folded on one side. It is commonly found in flowers of the family Fabaceae.

4. Vexillary aestivation: In this pattern, one large sepal or petal (called the vexillum or banner) completely covers the other smaller sepals or petals in the bud. It is commonly found in flowers of the family Fabaceae.

5. Contorted aestivation: In this pattern, the sepals or petals are twisted or contorted in different directions. It is commonly found in flowers of the family Solanaceae.

Conclusion:
Aestivation is an important characteristic that helps in the identification and classification of different flower species. It describes the arrangement of sepals or petals in relation to each other in a flower bud. Understanding aestivation patterns can provide valuable information about the evolutionary relationships and ecological adaptations of plants.