1. Carbon (C), nitrogen (N) and phosphorus (P) stoichiometries play critical roles in the function and structure of ecosystems by affecting important ecological processes. Yet, most studies to date have concentrated on foliar stoichiometry of phylogenetically distantly related species. 2. Here, we hypothesized that (i) plant stoichiometry of closely related species still shows biogeographic patterns because of the geographic patterns of abiotic environment at the regional scale and (ii) even related species still differ strongly in their stoichiometry owing to inherent differences in the absorption and retention of different elements. 3. To test the hypotheses, we analysed the C:N:P stoichiometry of 48 species of Artemisia and its close relatives from 65 sites across northern China. 4. Elemental concentrations and stoichiometry had no correlation with latitude or longitude but showed clear altitudinal trends. Climate had a weak effect on plant elemental concentrations and stoichiometry but not on C concentration. Soil chemistry had significant effects on C and P concentrations, C:P and N:P. Nested models revealed that species identity accounted for more than 30% of the total variance of all elemental concentrations and stoichiometric ratios, and different species responded differently to environmental gradients. 5. Synthesis. Our results highlight that even closely related species can vary importantly in plant elemental stoichiometry. This suggests that ecologists and global change researchers should be careful not to simply take a species’ stoichiometry as representative of an entire taxonomic group for upscaling of plant chemical responses to climatic and edaphic variation in our fast changing world.