Mosses may compete with vascular plants for limited soil resources, facilitate vascular plants by buffering extremes in abiotic conditions, and potentially trap seeds and provide safe sites for germination and establishment. We conducted a field study to investigate the effects of moss on the distribution and performance of Primula cusickiana var. maguirei, a threatened endemic perennial forb that occurs in an extremely narrow range within a single canyon in northern Utah, USA. Within the study population, we found that primroses occurred far more often on moss patches than on other substrates and that primroses occurring on moss patches had increased basal area and flower production. Furthermore, analyses revealed that soil under moss patches with primrose present had more organic matter, elevated magnesium concentrations, and lower Ca:Mg ratios. Our results suggest at least 3 hypotheses that may be evaluated through future studies. First, moss may facilitate P. cusickiana var. maguirei via the provision of increased soil resources. Second, moss may trap primrose seeds, leading to the observed pattern of distribution. and third, mosses and the primrose may both be responding to an as-yet-unmeasured habitat factor (e.g., soil depth or microtopography). Our results inform future research on P. cusickiana var. maguirei and have direct implications for the conservation of this threatened species.