Galls on plant leaves and stems are abnormal plant growths caused by insects, mites, or fungi whose activity triggers a short lived but permanent cancer-like growth. While galls may look alarming, most are harmless to plants. In Colorado, oaks, hackberries and cottonwoods often exhibit these small growths. Galls on stems and leaves can also serve as tiny ecosystems, housing larvae or spores. Galls are a testament to nature's complexity and are more of a curiosity than something to be concerned about.
Growing Home - Galls
