Zygomorphic ("yoke shaped", "bilateral") flowers can be divided by only a single plane into two mirror-image halves, much like a yoke or a person's face. Examples are orchids and the flowers of most members of the Lamiales (e.g., Scrophulariaceae and Gesneriaceae). Zygomorphic flowers generally have petals of two more different shapes, sizes, and colors.
Least commonly, flowers may have no axis of symmetry at all, typically because their parts are spirally arranged.
Read more about this topic: Floral Symmetry