Geometry integrates with lamina and petiole form and function under climatic gradients

Leaf geometry mediates the formal and functional integration of plant organs, yet how different geometric traits vary along environmental gradients and how they coordinate lamina and petiole traits, remains poorly understood. The study analyzed 1794 individuals spanning 294 woody plant species along a 4000-km latitudinal transect across China. We quantified the distribution and drivers of two key leaf geometric traits: leaf centroid ratio (LCR) and length to width ratio (LWR). In addition, we assessed how the coupling between geometry and lamina–petiole traits varied across spatial scales. We found that both geometric traits showed consistent declines with increasing latitude, primarily shaped by mean annual temperature and precipitation. LCR, a key regulator of biomechanical stability, showed the strongest connectivity in the lamina and petiole trait network at higher latitudes. LWR, reflecting efficiency in resource acquisition and conservation, maintained high and stable trait associations across all regions. In summary, our results suggest leaf geometric traits capture distinct functional axes of the lamina–petiole complex. This multidimensional framework advances our understanding of plant adaptive strategies and trait integration along environmental gradients.