The term zygomorphism, in botany, means that type of symmetry with a single fixed plane that can characterize some leaves (such as in ivy) or some types of bilabiata corolla flowers (such as in the scrofulariacee families and labiate).
The term zygomorphism comes from the two Greek words ζυγόν, zygon “yoke” and μορϕος, morphos, from the theme of μορϕή, morphé “form”.
The term zygomorph means, therefore, above all the irregular flowers that present a single plane of symmetry (bilateral symmetry).
In contrast to the term zygomorphs we have actinomorphs (or actinomorphs); in this last case we mean the flowers that instead will have more symmetry planes or radiated symmetry (as for example in the dipsacacee, composite, etc.).