Concept: This question tests your knowledge of aestivation, which refers to the mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl.

Why (A) is correct: In Calotropis (a member of the family Asclepiadaceae), the petals are arranged in a valvate aestivation. In valvate aestivation, the margins of adjacent sepals or petals just touch one another, without overlapping.

Why other options are wrong:

• (B) vexillary: Vexillary aestivation is characteristic of pea and bean flowers (Fabaceae), where the largest petal (standard) overlaps the two lateral petals (wings), which in turn overlap the two smallest anterior petals (keel).
• (C) imbricate: Imbricate aestivation involves overlapping margins, but not in a particular direction. One petal is interior, one is exterior, and the rest are overlapping.
• (D) twisted: Twisted aestivation occurs when one margin of the appendage overlaps that of the next one, and so on, in a regular manner, like in cotton, china rose, and lady's finger.

NEET Tip: Remember specific examples for each type of aestivation. For valvate, think of Calotropis and mustard. For twisted, think China rose, cotton. For imbricate, think Cassia, Gulmohar. For vexillary, think pea, bean.

Correct Answer: (A)