Terrestrial mosses dehydrate and go quiescent between precipitation events. Although many mosses are found in cool, low light environments, a number are abundant in drylands. We investigated the effects of ultraviolet (UV) radiation on the desert moss Syntrichia caninervis. This species is highly desiccation tolerant; it can lose almost all of its cellular water and recover after rehydration. In nature, desert mosses not only have to withstand the damage of desiccation itself but must also be able to recover from any damage incurred while dry, or have adequate mechanisms for injury prevention. They have no ability for active repair when quiescent and face risk of damage to sensitive molecules, including DNA, which absorbs UV wavelengths. We used chlorophyll fluorescence and high performance liquid chromatrography (HPLC) in a field experiment to better understand the role of UV on photosynthesis and the dimensions of UV tolerance in S. caninervis.