Multiscale surface metrology of dorsiventral leaf architecture in <i>Couepia bracteosa</i> : integrating ISO 25178 parameters, power spectral density, and fractal analysis

Abstract Surface architecture plays a fundamental role in governing the interaction between biological interfaces and their surrounding environment. In this study, we present a comprehensive multiscale surface metrology analysis of the adaxial and abaxial leaf interfaces of Couepia bracteosa a combination of optical microscopy, scanning electron microscopy, and three-dimensional confocal profilometry. Quantitative characterization was performed according to ISO 25178-2 areal surface texture parameters complemented by power spectral density (PSD) analysis, Hurst exponent estimation, fractal dimension (FD) evaluation, and Hough transform-based structural mapping. The results reveal two distinct surface regimes. The adaxial interface exhibits a comparatively smooth and spatially coherent topography, with low roughness amplitude ( S q = 1.0 ± 0.2 µ m) and near-Gaussian height distribution. In contrast, the abaxial interface presents a highly heterogeneous and hierarchically structured surface, characterized by a significant increase in roughness ( S q = 10 ± 1 µ m), broader height distributions, and reduced spatial persistence. PSD analysis demonstrated a decrease in the Hurst exponent (from 0.66 to 0.38) and a corresponding increase in the FD (from 2.34 to 2.62), indicating enhanced multiscale irregularity. Hough transform analysis further revealed an increased orientational dispersion on the abaxial surface. These findings demonstrate that dorsiventral leaf asymmetry corresponds to a transition between two distinct topographic regimes, governed by differences in amplitude, spatial organization, and hierarchical complexity. This study highlights the relevance of advanced surface metrology tools for the quantitative description of biological interfaces and provides a framework for linking multiscale surface architecture to functional interactions in natural systems.