Perianth
The floral envelope surrounding a flower’s reproductive organs, formed by distinct calyx and corolla or by undifferentiated tepals.
Calyx: The outer floral whorl, usually composed of sepals. It forms the outer part of a differentiated perianth.
Floral organ identity: The developmental specification of floral organs as sepals, petals, stamens, or carpels. Organ-identity programs determine whether floral parts differentiate into sepals and petals.
Floral formula: A symbolic notation summarizing the number, fusion, symmetry, and arrangement of floral parts. Floral formulas record whether a perianth has distinct whorls or tepals.
Perigone: A term for an undifferentiated floral envelope, especially one composed of tepals. It is often used for a tepal-bearing perianth rather than distinct calyx and corolla.
Corolla: The floral whorl composed of petals, usually inside the calyx. It forms the inner part of a differentiated perianth.
ABC model of flower development: A genetic model explaining floral organ identities through combinations of A-, B-, and C-class gene activities. Its gene combinations explain the developmental distinction between perianth whorls.
Floral diagram: A schematic cross-sectional representation of the number, arrangement, and fusion of floral organs. Floral diagrams make perianth whorls and their positions visible.
Androecium: The collective term for the stamens of a flower. It is a reproductive floral whorl, unlike the usually sterile perianth.
Tepal: A floral segment in an undifferentiated perianth, not clearly identifiable as a sepal or petal. Tepals make up the perianth when its two whorls are not distinct.
Floral symmetry: The arrangement of floral parts around one or more axes of symmetry. Perianth arrangement contributes to a flower’s overall symmetry.