While Sarracenia petioles, phyllodia, leaf plasticity, and seasonal pitcher cohorts are common subjects of discussion, these features have not yet been clearly delimited or described. Longitudinal allometry disclosed new substructures of the Sarracenia pitcher leaf on the first and climax leaf cohorts of several taxa with upright leaves. Petioles, previously thought to comprise the entire solid proximal portion of leaves, are found to be different from pitcher phyllodes, the two being adjacent but independently plastic substructures. Leaf cohort heterophylly is characterized by different substructure proportions and their constituent plastic properties. A locus at the transition point of internal pitcher chamber Zones 3 and 4 separates the inferior from superior lamina and damps the influence of plastic substructures in derived indices, including the inferior lamina to whole leaf longitudinal allometric index. This index helps distinguish cohorts within taxa and taxa from each other as its degree of relative variability is exceptionally low and consistent. The inferior lamina index and its core locus provide modular solidarity to the methodology, facilitating comparative analysis of substructures, the inferior and superior lamina, leaf cohorts, and taxa by means of allometric indices and their relative variability. Inferior lamina substructures facilitate known conditional responses in upright Sarracenia, with critical differences between taxa bearing implications for systematics.