The key difference between actinomorphic and zygomorphic flower is that actinomorphic flower is a flower that is radially symmetrical and can be divided into two equal parts along any diameter while zygomorphic flower is a flower that is bilaterally symmetrical and can be bisected into two equal parts only in one plane.
Floral symmetry explains whether the flower can be bisected into mirror images. Some flowers are radially symmetrical while some flowers are bilaterally symmetrical. However, some flowers are asymmetrical. Flowers with radial symmetry can be bisected into identical halves along any diameter. Those flowers are called actinomorphic flowers. In contrast, flowers with bilateral symmetry can be bisected into two identical halves in only one plane. Those flowers are called zygomorphic flowers.