Fungal endophytes comprise one of the most ubiquitous groups of plant symbionts, inhabiting healthy leaves and stems of all major lineages of plants. Together they comprise immense species richness, but little is known about the fundamental processes that generate that diversity and maintain their evolutionary success as plant symbionts. Community structures of foliar fungal endophytes depend mostly on host taxa and climate, but other environmental variables, such as soil type, plant physiology, neighboring plant community, are largely unexplored. Our goals are to understand how and why community structures change across environmental gradients as well as understand what ecological factors may lead to hyperdiverse communities of endophytic fungi.