Allometric analysis of four Hydrangea species (Hydrangea petiolaris, Hydrangea paniculata, Hydrangea macrophylla var. megacarpa and Hydrangea hirta) was conducted to test the hypothesis that the liana species (H. petiolaris) invests more in leaves and reproductive organs than the shrub species. We calculated the allocation ratios of leaves, supporting tissues (trunks and roots) and reproductive organs. Hydrangea petiolaris differed markedly from the three shrubs in terms of trunk and root allocations, while leaf allocation was not statistically different. The C/F ratios (the ratios of the dry weights of non-photosynthetic organs to photosynthetic ones) of the four species ranged from 9 to 12, and were not statistically different. These results did not support the hypothesis. The biomass of H. petiolaris was up to 100-fold greater than the biomass of the three shrubs. The growth form of H. petiolaris would minimize allocation to supporting tissue and produce a large biomass. The biomass of reproductive organs of H. petiolaris was up to 700-fold greater than the biomass of the three shrubs. This advantage might, therefore, serve as a driving force for the evolution of lianas.