A leaf shows damage caused by necrosis (cell death) and chlorosis (insufficient chlorophyll production) due to a pathogenic fungus. Such damage reduces the photosynthetic area available to the plant. Symbiotic fungi play key ecological roles in tropical forests. Symbiotic fungi can be mutualistic or pathogenic, and they can affect the health and function of individual plants, the dynamics of population dynamics, and the structure of communities. This photograph originally appeared on the cover of Ecology (88:3) in March of 2007.