Long-term effects of elevated CO2 concentration (ambient plus 350 μmol mol−1) on leaf photosynthetic acclimation of two species of a scrub-oak community, Quercus myrtifolia Willd. and Quercus geminata Small, were studied. Plants of both species were grown in open-top chambers in their natural habitat at Kennedy Space Center, Florida, USA. Compared to ambient CO2, elevated CO2 stimulated photosynthetic rates by 73 and 51% for Q. geminata and Q. myrtifolia, respectively. Maximum rate of carboxylation (Vcmax) was significantly reduced by elevated CO2 in Q. myrtifolia (28%) but not in Q. geminata. Maximum rate of potential electron transport (Jmax) was not significantly reduced by elevated CO2 in either species. In response to elevated CO2, specific leaf area decreased in Q. myrtifolia (22%), but not in Q. geminata. Elevated CO2 caused a significant accumulation of sugars (54%) and starch (264%) in Q. myrtifolia leaves, but not in Q. geminata leaves. Total Rubisco activity in Q. myrtifolia leaves was reduced 40% by elevated CO2, whereas no significant reduction occurred in Q. geminata leaves. Although both species share a common habitat, they exhibited marked differences in photosynthetic acclimation to elevated CO2 concentration.