Disentangling shape and size variation to compare canopy architecture in maize

{middle dot} Comparing maize canopies is confounded by two problems: plants differ in the number of phytomers they produce, and phytomer size scales with that number. Position along the shoot is therefore an unreliable basis for comparison, confounding shape with size. {middle dot} We first position the floral transition (tassel initiation, T.I.) within shoot development, revealing it as the landmark that organizes a conserved canopy shape. This provides the foundation for aligning canopies that differ in phytomer number. {middle dot} Focusing on the leaf blade, we used functional data analysis on a maize panel across controlled and field environments to decompose variation in blade-length profiles, which was dominated (77%) by overall amplitude, identifying scaling as the major source of size variation. Because blades enlarge with each phytomer until the transition, later T.I. yields a larger maximum; this T.I.-linked component explains up to one-third of scaling variation, reinforced by a shared genetic association between T.I. and blade size with the flowering-time gene ZmCCT10. {middle dot} Regressing out this component leaves a residual that defines a new, heritable axis of intrinsic scaling, independent of flowering time. It distinguishes hyper- and hypo-scaling genotypes consistently across environments, offering a selection target decoupled from phenology.