AbstractThe desiccation-tolerant moss,Grimmia laevigata, dominates the vegetation on exposed granitic boulders at a semi-arid site in southern California but fails to occur in especially xeric microsites, on overhanging surfaces, and on boulders of southfacing hillsides. It was hypothesized that establishment, rather than adult survival, limits the microdistribution of the moss. As predicted, adult plants transplanted to these microsites outside the observed microdistribution of the species showed no evidence of reduced function after one year. However, direct studies of establishment are required to confirm the hypothesis. Differences in net photosynthesis and chlorophyll content among transplants suggested that these characteristics were phentotypically plastic and changed with light availability. In the absence of potential photodamage,G. laevigatacan completely conserve chlorophyll during desiccation for at least twenty months.