Leaf stomatal characters influence the response of terrestrial evapotranspiration to climate change and are used as proxies for the reconstruction of past atmospheric 2>. We examined the phenotypic response of stomatal index (SI), density (SD) and aperture (AP) to rising atmospheric CO2 in 15 species after four years exposure to a field CO2 gradient (200 to 550 ¿mol mol-1 atmospheric 2>) or at three Free Air CO2 Enrichment (FACE) sites. Along the CO2 gradient, SI and SD showed no evidence of a decline to increasing 2>, while AP decreased slightly. There was no significant change in SI, SD or AP with CO2 across FACE experiments. Without evolutionary changes, SI and SD may not respond to atmospheric 2> in the field and are unlikely to decrease in a future high CO2 world.