<p>Foxglove (<i>Digitalis purpurea</i>) produce cardiac glycosides that are widely used in cardiovascular therapy. To enhance cultivation efficiency and increase metabolite yield, it is essential to understand how photosynthetic induction varies with leaf developmental stage. This study examined the dynamic changes in photosynthetic parameters during induction across young (YL), fully expanded (FEL), and old leaves (OL) of foxglove, and identified the predominant limitations constraining photosynthetic efficiency. FEL exhibited the highest net photosynthetic rate (<i>A</i>), carboxylation capacity (<i>V</i>_<i>cmax</i>), and cumulative carbon gain. However, the time required to reach 90% of <i>A</i> and <i>V</i>_<i>cmax</i> did not differ significantly among the three leaf types. Steady-state stomatal conductance was also comparable. Despite similar induction kinetics, YL showed the greatest carbon loss ratio, whereas FEL and OL displayed similar levels of loss. Limitation analysis revealed that stomatal factors predominated in YL and OL, accounting for approximately 70% of total photosynthetic limitation, while FEL exhibited a more balanced contribution from stomatal and biochemical limitations. Since mesophyll conductance (gₘ) was not measured independently, its effects were likely included within the biochemical component, potentially leading to an overestimation of biochemical limitation in FEL. The consistent induction speed across developmental stages supports simplification in modeling canopy-level photosynthesis in foxglove. These findings also inform the development of dynamic lighting strategies in controlled environments. In summary, these findings highlight stomatal regulation as a primary constraint on photosynthetic induction, thereby establishing a physiological basis for enhancing productivity and cardiac glycoside accumulation in foxglove cultivation.</p>