Floral symmetry is associated with contrasting hydraulic strategies and trait coordination in angiosperm flowers.

Abstract

Floral symmetry is widely recognized as a key driver of angiosperm diversification, yet how actinomorphic and zygomorphic flowers differ in their hydraulic architecture remains poorly understood. Clarifying symmetry-related differences in hydraulic strategies is essential for linking floral function with physiological and evolutionary divergence. Here, we measured 22 floral traits related to hydraulics, structural and reproductive investment across 39 woody species (21 actinomorphic and 18 zygomorphic) to evaluate how floral symmetry shapes hydraulic design. Our results revealed distinct hydraulic differentiation between the two symmetry types. Zygomorphic flowers exhibited significantly longer floral longevity (FL) and lower petal vein density (D _vein) than actinomorphic flowers. They also adopted a hydraulically safer strategy, characterized by more negative water potential at the turgor loss point (ψ_tlp), lower relative water content at turgor loss (RWC_tlp), and higher hydraulic capacitance (C _1,mass). Crucially, after accounting for native climatic variables, divergence in FL, ψ_tlp, and D _vein remained significant, indicating that these traits represent intrinsic features of floral symmetry, whereas C _1,mass and RWC_tlp function primarily as environmentally plastic responses. Functionally, actinomorphic flowers prioritized hydraulic supply capacity, whereas zygomorphic flowers combined enhanced hydraulic safety with extended longevity. Furthermore, zygomorphic flowers showed stronger trait coordination, forming integrated functional modules that likely contribute to greater hydraulic stability under fluctuating environmental conditions. Together, these findings demonstrate that floral symmetry is tightly linked to physiological function and that evolutionary shifts in symmetry may be accompanied by coordinated adjustments in hydraulic safety as well as structural and reproductive investment, thereby supporting divergent pollination strategies and life-history demands.