Identifying the impact of phylogeny and environmental change on variation in plant traits is an important component of attempts to understand the adaptability and response of vegetation to environmental change. The relationship between plant functional traits and environmental change is easier to measure with consistent phylogeny. In the study reported here we analyzed the source of variation of six plant functional traits in 47 species from 19 sample sites in the Yanhe river watershed of China. The 19 sample sites surveyed in this study were selected based on the climatic gradient, as represented by vegetation zonality. The six plant functional traits investigated were specific leaf area (SLA), specific root length (SRL), and the mass-based characteristics of leaf nitrogen concentration (LN), leaf phosphorus concentration (LP), root nitrogen concentration (RN), and root phosphorus concentration (RP). To analyze the impact of environmental change on variation in plant traits, we also selected terrain factors and soil moisture content as environmental variables. We then used variance analysis to differentiate the relative influence of phylogenetic background (as represented by plant family), climatic conditions, terrain factors, and soil moisture content on trait variation, and used a stepwise regression method to analyze the response of traits to environmental change in plants sharing a similar hereditary background. Our results include the following observations: (1) significant differences were uncovered with respect to SLA, LN, and RP under different climatic conditions. We found that SLA and RP of forest plants were 33% and 20% higher respectively, than SLA and RP of steppe plants, whereas LN of plants from steppe sites was 19% higher than that of plants from forest sites. Significant differences were also detected in SLA, SRL, LN, and RN among different families. Average SLA, LN, and RN values measured from Leguminosae species were 16%, 65% and 98% higher respectively, than average values obtained for all studied plants. Species from the family Poaceae had the highest SRL, which was 1.03-fold higher than the overall average; (2) variation of plant functional traits was mainly determined by plant phylogenetic background, which accounted for 27.86, 32.78, and 42.70% of observed variation in SRL, LN, and RN, respectively. On the other hand, LP and RP were mainly influenced by the environment, which accounted for 24% and 15.58%, respectively, of observed variation in LP and RP; (3) stepwise linear regression models revealed that species from different families responded differently to environmental factors. Members of the families Leguminosae and Poaceae were more sensitive to regional hydrothermal conditions, whereas Asteraceae and Rosaceae species were more strongly affected by local microenvironments. After removing influences attributable to phylogenetic background, we were able to clearly and reliably discern relationships between functional traits and the environment. In the Yanhe river watershed, plant phosphorus content was mainly determined by terrain factors and soil moisture content. In contrast, plant nitrogen content, SLA, and SRL were mainly affected by plant phylogenetic background. To summarize, plant phylogenetic background plays a controlling role in the influence of the environment on plant traits in the Yanhe river watershed of China.