Phyllody is the development of floral parts into leafy structures, generally caused by virus or phytoplasma infection such as aster yellows. Evidence suggests that the phytoplasma downregulates a gene involved in petal formation, instead causing leaves or leaflike structures to form. Phyllody causes the affected plant to become partially or entirely sterile, as it is unable to normally produce flowers. This can also happen in some cultivars of roses apparently without infection.[1]