Corolla with four diagonally arranged petals is

A. Vexillary corolla has five petals of different shapes called the standard, wings and keel. Standard overlaps the wings which then overlap the keel. It is found in Papilionaceae.

B. Cruciform corolla has diagonally arranged petals.

C. Corolla with fused petals is called gamopetalous.

D. Caryophyllaceous corolla has five free clawed petals whose limbs are at right angle to the claws, as found in the family Caryophyllaceae.

Hence, the correct answer is 'Cruciform.'