Zygomorphy

Zygomorphy, also called zygomorphism, is the condition of having a single plane of symmetry, such that a body or structure can be divided into two mirror-image halves along one vertical plane. The term derives from Greek zygos, meaning “yoked” or “paired,” and morphe, meaning “form.”

In botany, zygomorphic flowers are bilaterally symmetric, in contrast to actinomorphic flowers, which are radially symmetric and can be divided into multiple equal planes. Zygomorphic flowers often appear with specialized shapes that guide pollinator interactions, and they are common in several plant families. Notable examples include many Fabaceae (peas and beans) and Orchidaceae species, as well as snapdragons (Antirrhinum). The evolution of zygomorphy in flowers is frequently linked to pollination strategies and floral organ arrangement, which can influence pollinator behavior and efficiency.

In zoology, the preferred term for left–right symmetry is bilateral symmetry. While most animals exhibit bilateral symmetry, the term zygomorphy is less standard in describing entire organisms and is more often reserved for particular structures or for historical usage. When employed in zoological contexts, it generally denotes a single-plane symmetry concept similar to the botanical sense, but the broader and more accepted term remains bilateral symmetry.

See also: bilateral symmetry, actinomorphy, floral morphology, pollination biology.