tetramerous

Tetramerous is a botanical term describing floral parts that occur in fours. The word derives from the Greek tetra- meaning four and meros meaning part, and it is used to describe the number and arrangement of organs within a flower.

In plant descriptions, tetramerous refers to a flower whose perianth segments—typically petals and sometimes sepals—are organized in whorls of four. This four-part arrangement is most often observed in petals, but may also pertain to other floral organs. The term is commonly used in contrast to pentamerous (five parts) and trimerous (three parts), reflecting differences in floral symmetry and developmental patterning.

Common examples occur in several dicot groups. The Brassicaceae (mustards and crucifers) frequently display tetramerous flowers, with four petals forming a cross-shaped corolla. Poppies in the Papaveraceae and related families also often exhibit four petals. While tetramerous flowers are widespread in certain lineages, many plants show different part numbers, such as pentamerous or trimerous configurations, depending on evolutionary history and functional morphology.

Outside of botany, the term tetramerous is rarely used, though it may appear in historical or comparative descriptions of four-part structures in other organisms. In modern usage, the term is primarily a botanical descriptor of floral morphology and is most helpful when contrasting four-part patterns with other common floral schemas.

See also: pentamerous, trimerous, cruciform flower, actinomorphic, zygomorphic.