Photosynthesis in a deciduous forest understory was studied for three exotic vine species (Pueraria lobata Lonicera japonica and Hedera helix) and five common native species (Rhus radicans [Toxicodendron radicans] Clematis virginiana Smilax rotundifolia Vitis vulpina and Parthenocissus quinquefolia) possessing a variety of climbing mechanisms. The adventitious-root climbers (H. helix and R. radicans) had the lowest maximum photosynthetic rates of all species (5.5 and 6.4 µmol m-2s-1 respectively). The twining vine P. lobata was the least adapted to the understory with a high light-compensation point (43 µmol m-2 s-1) low photosynthesis under low light (0.5 µmol m-2 s-1 at 50 µmol m-2 s-1) and the highest light requirement for obtaining 90% of maximum photosynthesis (860 µmol m-2 s-1). Lonicera japonica another twining vine was better-adapted to low light conditions but vines with tendril climbing mechanics were physiologically the best adapted to low light. The adhesive-tendril climber P. quinquefolia was the best adapted to shade with a low light compensation point (20 µmol m-2 s-1) a high photosynthetic rate under low light (3.5 µmol m-2 s-1) and a low light saturation point (160 µmol m-2 s-1). The results suggest that physiological adaptability of vines to low-light environments may be related to climbing mechanics.