Symmetrical bilaterally; -- said of organisms, or parts of organisms, capable of division into two symmetrical halves only in a single plane.

(Gr. zygos: yoke; morphê: shape) adj. Bilaterally symmetrical, so that a line drawn through the middle of the structure along only one plane will produce a mirror image on either side. Said of the corolla or calyx when divisible into equal halves in one plane only bilaterally symmetrical, with only one plane of symmetry, usually the plane that bisects the flower vertically. Of a flower divisible into similar halves by only one plane of symmetry. Cf. actinomorphic, and see irregular. Also zygomorphous.

capable of division into symmetrical halves by only one longitudinal plane passing through the axis