Both Panax ginseng Meyer and Panax quinquefolius are obligate shade-loving plants whose natural habitats are broadleaved forests of Eastern Asia and North America. Panax species are easily damaged by photoinhibition when they are exposed to high temperatures or insufficient shade. In this study, a cytohistological study of the leaf structures of two of the most well-known Panax species was performed to better understand the physiological processes that limit photosynthesis.