Low size inequality in stomatal area distributions detected for 12 tree and shrub Magnoliaceae species: evidence of hydraulic optimization

We propose that the reticulate venation network characteristic of Magnoliaceae species creates small, well-defined regions (i.e. areoles) where stomata experience a uniform hydraulic supply. This epidermal bauplan should minimize developmental variation in stomatal size, resulting in a low size variance and symmetric contributions of differently sized stomata to stomatal area distributions. To test this hypothesis, we quantified the stomatal area size distributions in 12 Magnoliaceae species using a Lorenz curve approach fitted via a generalized performance equation (GPE). Analysis of 69,931 stomata confirmed an exceptional model fit and provided strong support for our hypothesis, i.e. the Gini coefficient values were low (mean ± standard deviation: 0.057 ± 0.014), whereas the Lorenz asymmetry coefficients clustered tightly around 0.505 ± 0.037, indicating symmetric distributions where no size class disproportionately contributed to inequality. These results indicate (1) a consistent hydraulic homogeneity at the areole level, and (2) reticulate hierarchical venation networks enforce developmental regularity, constraining stomatal size variation and eliminating the numerical dominance of extreme phenotypes. Our mathematical approach (1) provides a robust tool for quantifying biological inequality, (2) provides insights into how leaf hydraulic architecture fundamentally shapes cellular-level trait distributions, and (3) establishes a mechanistic link between venation patterns and stomatal uniformity, with implications for understanding plant adaptation, gas exchange efficiency, and developmental stability under environmental constraints.