The atmospheric CO₂ concentration [CO₂] is rising markedly and is expected to be approximately 40% higher in 2050 than today. Although the short-term plant responses to elevated [CO₂] have been well studied, much less is understood about evolutionary responses to high [CO₂]. Natural CO₂ spring, where [CO₂] has been consistently high, enables us to study plants exposed to high [CO₂] over an evolutionary time scale. We conducted a common-garden competition experiment using Plantago asiatica seeds acquired from three natural CO₂ springs and the control sites. In open top chambers with elevated growth [CO₂] (700ppm) and ambient growth [CO₂] (around 400ppm), P. asiatica of each spring and the respective control were cultivated in pots; each pot had 4 spring and 4 control plants. Vegetative growth and the productions of reproductive organs were investigated. Although results of vegetative growth did not show a consistent tendency among three springs, the results of reproductive production suggest that plants originated from all three springs were more competitive against their respective control plants under elevated growth [CO₂] than in ambient growth [CO₂]. These results support that atmospheric CO₂ elevation can act as a selective agent in natural plant populations.