Abstract: Aims Leaf vein networks reflect plant hydraulic efficiency and ecological strategies. Traditionally, vein density is considered to be primarily constrained by climatic factors, particularly water conditions. However, whether conclusions derived from the physiological mechanisms of extant species can effectively explain trait evolution-ary patterns on a macro-evolutionary deep-time scale remains a subject of significant controversy. This study aims to systematically explore the evolutionary trajectory of vein density and its potential driving factors. Methods We integrated vein density data from 2,642 extant species globally and 41 Cenozoic fossil plant mor-photypes. By combining high-resolution paleoclimate records with data on insect species diversity across geolog-ical periods, we analyzed the evolutionary patterns using phylogenetic comparative methods and time-series analyses. Important findings 1) In a phylogenetic context, the vein density of extant species is correlated with annual precipitation and precipitation seasonality; 2) On a geological time scale, the long-term evolutionary trend of vein density is consistent with the trend of global climate change, but single climatic factors fail to fully explain the evolutionary variation of vein density; 3) The diversification of generalist herbivorous insects is synchronous with the long-term variation trend of vein density, showing a significant positive correlation. These results reveal that the evolution of angiosperm vein density in the Cenozoic was not driven solely by environmental factors but may also be an adaptation to the feeding pressure brought by the diversification of herbivorous insects. This study highlights the key driving role of biotic interactions in the macro-evolution of plant traits.

Key words: Angiosperms, Leaf vein density, Herbivory pressure, Climate adaptation, Macroevolution, Cenozoic