The development of the plant shoot is a remarkable feat of cellular coordination. Genes control the identity, differentiation, and proliferation rates of cells in the developing plant. Yet, understanding how these genes function together across space and time among heterogenous populations of cells remains a problem. In this dissertation, I first provide an introductory review of the developmental genetic coordination of axial (proximodistal, adaxial-abaxial, and mediolateral) genetic patterning modules that function during leaf development, arguing that such cross-talk between patterning networks results in the reproducible phenotypic outcomes of morphogenesis. I next present single-cell transcriptomic analyses of the developing maize seedling shoot apex with the goal of identifying, in an unbiased fashion, the organization of cell types and gene expression signatures in the developing shoot, including the pluripotent shoot apical meristem (SAM). These analyses identify a slowly-proliferating stem cell population with gene expression signatures indicative of active maintenance of genome integrity. More actively proliferating daughter cells at the periphery of the meristem contribute the raw material for organ initiation. Surprisingly, we did not identify a canonical WUSCHEL-expressing stem cell organizer. Through the use of pseudotime analysis, I use these single-cell RNA-seq data to infer the gene expression changes associated with cell differentiation along the proximodistal leaf axis, and propose a role for the meristem indeterminacy gene KNOTTED1 in promoting leaf development through the regulation of sheath identity. In the third chapter of this dissertation, I present evidence that development of both the maize ligule and the leaf margin make use of an ‘edge’ genetic patterning module, characterized by redundant WOX3 gene function. I show that the edge program in the ligule is associated with juxtaposed domains of adaxial-abaxial patterning gene expression, similar to what is observed at the growing leaf edge. Computational modeling of the developing ligule indicates that such juxtaposition of adaxial-abaxial patterning gene function is sufficient to promote WOX3-driven outgrowth of the ligule. Together, these cellular scale analyses of shoot patterning shed light on the developmental genetic regulation of organogenesis in the plant shoot, as well as the recruitment of an extant patterning module to create morphological novelty.