bilateral symmetry

The arrangement of parts in an organ or organism such that it can only be split into similar halves along one given plane. Thus most leaves can only be divided into similar halves by cutting along the midrib. Bilateral symmetry in flowers is usually termed zygomorphy. The flowers of relatively advanced angiosperm families, e.g. Scrophulariaceae, are often zygomorphic. In a floral formula, zygomorphy is represented by the symbol •|• or ↑.