Plant leaf vein traits are partially the result of adaptation to environmental factors during long-term evolution. For terrestrial plants, leaf veins greatly vary in size and numbers. Parrotia subaequalis (H. T. Chang) R. M. Hao et H. T. Wei, an endangered tree species endemic to China, has a limited distribution, and inhabits both hillsides and valleys. The variations in P. subaequalis leaf venation and vein density in response to environmental changes were examined by collecting samples from all 14 extant populations and analyzing the association between leaf vein density and environmental factors. The results revealed that leaf characteristics were strongly associated with different habitats. A set of vein traits, namely base angle, intercostal tertiary areole development and shape, and free ending veinlet branching, were related to habitat. Significant relationships between vein density and environmental variables (mean annual temperature, mean annual precipitation, and elevation) were doubtless confirmed by this study. These findings indicate that phenotypic plasticity in leaf vein traits is an important ecophysiological characteristic that enables P. subaequalis to adapt to spatiotemporally fluctuating environments. Furthermore, these results also provide important reference data for in-depth studies on the protection strategies used by the tree.