Rose flowers sometimes develop green, leaflike structures. This uncommon abnormality is called phyllody. Certain rose varieties (e.g., floribundas) more often develop phyllody.
Green, vegetativelike structures develop where rose flower parts such as pistils and stamens normally occur. When roses have both normal and abnormal flowers but foliage growth and color look healthy, the cause is probably abiotic, due to adverse environmental conditions. When mild weather returns, the subsequent flowers should develop normally if the cause of phyllody is abiotic.
Phytoplasmas and viruses can also cause phyllody in many plant species, but not commonly in roses. If phyllody occurs on roses with stunted growth or foliage that is yellow or otherwise unhealthy, a phytoplasma or virus may be the cause.
Phyllody apparently is due to a plant hormone imbalance when flower buds are forming. In roses, usually hot weather or drought stress during flower bud formation are the cause of hormone imbalance.
Infection by phytoplasmas or viruses can also disrupt plant hormones in roses and affect flower appearance. Because these pathogens typically alter foliage appearance, whether or not leaves appear healthy indicates whether the cause of phyllody is abiotic or pathogenic microorganisms.
Phyllody does not seriously harm plants. The atypical appearance of blossoms can be aesthetically undesirable.
There is no management other than pruning out affected blooms and providing plants with good growing conditions and proper cultural care. Consult Phyllody in Roses and Pest Notes: Roses: Diseases and Abiotic Disorders for more information.