资源环境科技发展态势分析平台

C-4 photosynthesis is a complex trait that boosts productivity in warm environments. Paradoxically, it evolved independently in numerous plant lineages, despite requiring specialised leaf anatomy. The anatomical modifications underlying C-4 evolution have previously been evaluated through interspecific comparisons, which capture numerous changes besides those needed for C-4 functionality. Here, we quantify the anatomical changes accompanying the transition between non-C-4 and C-4 phenotypes by sampling widely across the continuum of leaf anatomical traits in the grass Alloteropsis semialata. Within this species, the only trait that is shared among and specific to C-4 individuals is an increase in vein density, driven specifically by minor vein development that yields multiple secondary effects facilitating C-4 function. For species with the necessary anatomical preconditions, developmental proliferation of veins can therefore be sufficient to produce a functional C-4 leaf anatomy, creating an evolutionary entry point to complex C-4 syndromes that can become more specialised.