Mechanisms underlying green flower formation.

Green flowers are uncommon in nature, yet they present a unique opportunity to explore the molecular, developmental, and evolutionary principles underlying floral pigmentation. While most species undergo petal degreening during maturation, some retain chlorophyll through suppressed degradation, sustained synthesis, or altered plastid differentiation. Here, we synthesize recent advances in understanding the molecular basis of green flower formation, integrating evidence from plastid biology, chlorophyll metabolism, transcription factor regulation, and floral organ identity genes. Research across diverse taxa reveals that chlorophyll homeostasis in petals is shaped by the interplay of light and hormonal signals, and orchestrated by transcriptional networks. In certain instances, homeotic transformations result in leaf-like characteristics. Naturally occurring variants, as well as engineered lines, offer powerful systems to dissect how developmental programs governing organ identity intersect with pigment metabolism. Green flowers also hold distinct ornamental and cultural value, expanding their relevance beyond ecological function. By tracing progress from morphological observations to multi-omics analyses, we highlight how this field is beginning to uncover shared regulatory frameworks and lineage-specific innovations. In the future, targeted manipulation of key regulatory nodes could enable the precise breeding of stable green blooms, while comparative studies promise deeper insights into how pigment pathways evolve and integrate with broader developmental networks. Understanding these processes will not only enrich floral biology but also enhance our ability to intentionally design and diversify plant phenotypes.