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Leaf venation and coupled physiological function of wild plants co-evolve during the natural selection. How artificial selection affects leaf vein traits and coordinated physiological functions of main crops are largely unknown. This study examined the changes of leaf vein traits and their correlation with gas exchange of flag leaves and yield in eight wheat genotypes of differing ploidy under the same growing conditions. The results indicate that flag leaf vein density (VLA), major-vein density (VLAmajor), and minor-vein density (VLAminor) decreased whereas the proportion of minor-vein length and interveinal distance between small longitudinal veins (IVD) increased during the polyploidization process, and the major advance occurred from the period from diploids to tetraploids. The VLA, VLAmajor, and VLAminor were closely coordinated with maximum net photosynthetic rate (PN) and photosynthetic N use efficiency (PNUE), but not with stomatal conductance. The proportion of minor-vein length and IVD were negatively related with PN and PNUE but positively related with N content per area (Narea) during wheat evolution. A higher proportion of minor-vein length and IVD, and a lower VLAmajor in flag leaves along with a larger Narea were largely responsible for the increased yield in modern cultivars. The decreased redundancy of leaf vein density and increased minor-vein proportion in modern cultivars can confer a yield advantage during wheat evolution.