This dataset contains the leaf traits, plant size and environment data of 262 individuals of a widespread species Clausena dunniana in the subtropical broad-leaved forests in Maolan National Nature Reserve in the karst region of southwestern China. The 262 individuals of C. dunniana are distributed at two major topographic habitat types, the slope and the hilltop, within the forests of six sites evenly distributed in two regions within the Maolan reserve. The measured individual plant level leaf traits include specific leaf area (SLA), leaf area, leaf dry-matter content (LDMC) and leaf thickness. The plant size represents the first principal component of plant basal diameter and plant height, and the environmental factors include topographic habitat, canopy height, and rock-bareness rate.