Leaf and floral architectures contribute significantly to crop yield. Leaf architecture, i.e., leaf length, width and angle, defines canopy structure, which influences light penetration, photoassimilate production and overall plant fitness. In the cereals, floral architecture defines the production and arrangement of the structures that bear grain, directly impacting yield. A major challenge in plant biology is to understand the genetic factors that regulate the development of leaf and flower parts, seemingly disparate, but evolutionarily related structures, in the grasses. We discovered and characterized a novel maize (Zea mays spp. mays) mutant we named drooping leaf1 (drl1), as acutely flaccid leaves lacked a functional midrib, akin to mutations in the single copy DL gene in rice. In pistillate and staminate florets, drl mutants displayed ectopic inner-whorl organs. These mutant phenotypes were drastically enhanced by a modifier locus in the Mo17 inbred line. We cloned the underlying gene, drl1-R, and identified its paralogous enhancer, drl2-M, using positional cloning. The genes encode the maize CRABS CLAW co-ortholog, a putative transcriptional regulator with zinc-finger and YABBY domains. Our data suggest natural variation in Mo17 at the drl2 locus likely enhances the drl1 mutant phenotypes; similar modifier alleles may exist in other diverse maize inbred lines. Genome wide association studies indicated the drl1 and drl2 loci are tightly linked to quantitative traits for leaf angle and width and internode length in the maize nested association mapping population. RNA in situ hybridization revealed that drl1 and drl2 transcripts accumulate in lateral primordia, but not in vegetative or floral meristems. However, expression from the drl loci influenced meristem activity, suggesting the drl genes may function non-cell autonomously. Genetic interactions with mutants that affect leaf and floral development demonstrated a requirement for the drl genes early in establishing leaf and floral architectures. This dissertation provides the first evidence of yabby function in maize, and illustrates the impact of the drl genes on leaf and floral development, important agronomic traits that influence yield in maize breeding lines.