Abstract
Allometry, the study of size and its effects on biological traits, provides a quantitative and predictive framework for the evolution of plant allocation strategies. While most studies focus on scaling relationships between distinct structures (e.g., leaves, stems, and roots), the allometry within reproductive structures remains underexplored. Here, we assess the global scaling of biomass within diaspores. We take an ecological and evolutionary perspective to examine the interspecific and phylogenetic allometry of within-diaspore (e.g., seeds, fruit) biomass allocation in plants worldwide. We compiled data on seed mass, fruit mass, and seed dispersal mode (biotic versus abiotic) from open-access databases and the literature for 346 species across 97 families to investigate how diaspore biomass is allocated and then consider how this pattern might be influenced by (i) evolutionary history and (ii) seed dispersal mode. Our results reveal that seed mass scales isometrically with fruit mass. This pattern persists after accounting for phylogenetic relatedness and seed dispersal mode despite a notable trend towards differences in allometric coefficients among groups. Our findings suggest that isometric reproductive scaling is a conserved evolutionary pattern shaped by a combination of selective trade-offs, developmental constraints and historical dispersal syndromes. By integrating scaling theory with evolutionary perspectives, our study advances a predictive framework for understanding plant allometry and its role in shaping reproductive strategies across diverse lineages.