petaloidy

Petaloidy is a botanical term used to describe petal-like tissue in flowers, typically arising when non-petal floral organs assume petal characteristics in form, texture, or appearance. It is most evident when stamens or staminodes become petaloid, producing flower parts that resemble petals. In some lineages, sepals or other organs can also become petaloid, leading to flowers with a petal-rich look while the underlying floral architecture differs from that of a typical ray.

Developmentally, petaloidy results from changes in the identity and differentiation of floral organs during growth. Alterations in gene regulation can cause parts that would normally become stamens or sepals to take on petal-like identity. In many accounts, this involves shifts in the networks described by the ABCDE model of flower development, where petal-identity programs expand into regions that would normally form reproductive or non-petal tissues. The outcome is an increased abundance of sterile, petal-like structures and often a reduction or loss of fertility.

Petaloidy is a common feature in many ornamental plants, contributing to the elaborate forms of double flowers. Familiar examples include certain double roses, carnations, and peonies, where stamen structures are largely or entirely replaced by petaloid tissue. The concept helps describe variations in flower morphology used in taxonomy, horticulture, and studies of floral development, and it highlights how changes in organ identity can reshape floral form without altering overall species identity.