Saxicolous lichens are a major, ecologically significant component of the biodiversity present in rocky outcrop habitats, including ultramafic outcrops. While multiple studies have investigated the biotas of ultramafic outcrops, few have directly compared ultramafic and non-ultramafic lichen communities. As a result, the importance of substrate factors (elemental composition, surface pH, microtopography) in relation to other abiotic factors is poorly understood for saxicolous lichen communities. In a regional community ecology study, we sampled lichen biotas of eight ultramafic and eight sandstone outcrops along a 70 km maritime influence gradient in order to test three hypotheses: 1) a substrate effect hypothesis that saxicolous lichen communities of ultramafic and sandstone outcrops are compositionally distinct; 2) a maritime gradient hypothesis that coastal and inland communities are compositionally distinct; and 3) a maritime moderation hypothesis that coastal ultramafic and sandstone communities are more similar than those of inland ultramafic and sandstone. Our results provide support for the substrate effect hypothesis and the maritime gradient hypothesis. Lichen communities of 1) ultramafic and sandstone outcrops and 2) coastal and inland outcrops were compositionally distinct. The maritime moderation hypothesis was not supported; lichen communities of ultramafic and sandstone outcrops were significantly differentiated across the maritime gradient. A total of 134 taxa were recorded - 81 taxa from ultramafic outcrops and 100 taxa from sandstone, with 47 taxa found on both rock types. Ultramafic outcrops were characterized by greater similarity between samples, lower lichen cover, larger differences in cover between north and south aspects, and higher abundance and diversity of cyanolichen taxa compared to sandstone. This study is one of few to quantitatively examine lichen communities of two rock types and is unique in that it does so at a regional scale. These results add to our understanding of the interactive roles of substrate and maritime influence in lichen community assembly.