SummaryStomata are epidermal valves that facilitate gas exchange between plants and their environment. Stomatal patterning is regulated by EPIDERMAL PATTERING FACTOR (EPF)-family of secreted peptides: EPF1 enforcing stomatal spacing, whereas EPF-LIKE9, also known as Stomagen, promoting stomatal development. It remains unknown, however, how far these signaling peptides act. Utilizing Cre-Lox recombination-based mosaic sectors that overexpress either EPF1 or Stomagen in Arabidopsis cotyledons, we reveal a range within the epidermis and across the cell layers in which these peptides influence patterns. To quantitatively determine their effective ranges, we developed a computational pipeline, SPACE (Stomata Patterning AutoCorrelation on Epidermis), that describes probabilistic two-dimensional stomatal distributions based upon spatial autocorrelation statistics used in Astrophysics. The SPACE analysis shows that, whereas both peptides act locally, the inhibitor, EPF1, exerts longer-range effects than the activator, Stomagen. Furthermore, local perturbation of stomatal development has little influence on global two-dimensional stomatal patterning. Our findings conclusively demonstrate the nature and extent of EPF peptides as non-cell autonomous local signals and provides a means to quantitatively characterize complex spatial patterns in development.Summary StatementNon-cell autonomous effects of activator and inhibitor peptides on 2-D spatial patterning of stomata were quantitatively characterized using chimeric sectors and a SPACE computational pipeline.