{In stream ecosystems, bryophytes greatly increase substrate heterogeneity and support a high density and diversity of lotic primary producers, such as epiphytic algae. However, there is little information about how the spatial distribution and density of epiphytic diatoms varies with respect to bryophyte morphology. This study examined epiphytic diatom communities from the contrasting bryophyte morphologies of mosses and liverworts. We predicted that mosses, with morphologies that create more crevices, would have a higher density of epiphytic diatoms than liverworts, with leaves highly exposed to the turbulence of the stream current. Six species of bryophytes (two mosses and four liverworts) were collected from streams in the Great Smoky Mountains National Park, and 37 species of epiphytic diatoms were identified on these bryophytes. Diatom density was significantly higher on the adaxial leaf surface of mosses compared to the abaxial leaf area (ANOVA