Bryophytes are often noted for their growth on specific rock types and their value as indicator species. However, some evidence suggests that restriction of a species to specific rock types may be less rigid and could vary under different environmental conditions. We assessed richness and distribution patterns of bryophytes at 22 rock outcrop locations in upstate New York (NY) and coastal Maine (ACAD). At each location, detailed surveys were done in five replicate 5-m by 2-m plots on vertical rock faces. We report on the 194 bryophyte species found in these surveys and present detailed analyses for the 137 species that occurred at two or more of the 22 locations. In general, liverworts were less likely to be dominant within a plot than mosses. Within-site dominance and frequency of liverworts were less well correlated to larger-scale frequency (number of locations and regions of occurrence). In NY, although there was no significant difference in bryophyte richness by rock type, rare species were more often found on calcium-containing rock types. Rock type, soil influence, number of liverwort species, and region were significant correlates with bryophyte species composition patterns. The importance of rock type in explaining species composition patterns was still significant though weaker when ACAD locations were included in the analysis. This difference resulted from a higher prevalence of leafy liverwort species on calcium-containing rock types in ACAD. Our results present further evidence that apparent restrictions to specific rock types may shift depending on environmental conditions such as increased humidity and narrower temperature extremes that occur along the north Atlantic coast.