We performed a comparative study of the vascular flora of a serpentine outcrop, Pine Hill, and that of a granite outcrop, Settlement Quarry, from Little Deer Isle and Deer Isle, respectively, Hancock County, Maine. We established four transects along a gradient from exposed to forested areas within each outcrop. Plants were recorded for presence and percent cover from circular plots along each transect. Soil and tissue samples were collected to examine soil-tissue elemental relations. One hundred thirty-two taxa were recorded from serpentine and 89 from granite. Fifty-seven taxa were shared by both sites. Species richness (α diversity) and diversity indices (Shannon-Weaver and Simpson) suggested significant differences between sites and within sites. Principle Component Analysis suggested substrates differed significantly between sites and between exposures within sites. Tissue analyses suggested intraspecific variation with respect to tissue elemental concentrations, especially in Achillea millefolium, Oenothera biennis, Prunus virginiana, Selaginella rupestris, Spiraea alba var. latifolia, and Vaccinium angustifolium. Serpentine populations of many taxa showed low tissue Ca∶Mg ratios (< 1) and high Ni concentrations. Two-way ANOVA showed significant substrate × species effects for several elements, including those that typically characterize serpentine substrates (Ca, Mg, Cr, Ni), suggesting significant genetic variation within species with respect to substrate. Finally, we compared our species list for Pine Hill with a plant survey done at Pine Hill and five additional serpentine sites of Maine in 1977 and provide a list of 285 vascular plant taxa from 62 families for serpentine in Maine.