The development of structural novelty is difficult to study, as novelty is ancient and lacks transitional forms. Mimulus gemmiparus, or Erythranthe gemmipara, reproduces almost entirely with a novel and asexual aerial bulbil. Within Mimulus, supernumerary axillary meristems are deposited in the leaf axils, where the leaf intersects the stem. For M. guttatus (E. guttata), M. floribundus (E. floribunda), and M. gemmiparus (E. gemmipara), the primary axillary meristem usually varies between becoming a branch or a flower. In M. guttatus and M. floribundus, the secondary axillary meristem may branch or flower (or remain quiescent) while in M. gemmiparus, the secondary axillary meristem typically expands into a vegetative propagule, which then arrests and is ensheathed by the subtending leaf petiole, resulting in a novel aerial bulbil that shares homology with both branches and leaves. To visualize the evolutionary divergence of whole plant and axillary meristem development in M. gemmiparus, I compared the growth of M. gemmiparus to two sympatric sister taxa, M. guttatus and M. floribundus. Throughout ontogeny, I measured height and node development to model the growth of the plants using a Function-Valued Trait (FVT) approach to determine how plant development has been modified to accommodate the novel reproductive structure in M. gemmiparus. Additionally, I imaged the development of axillary meristems over time within each species using scanning electron microscopy to create a cross-species comparative developmental series capturing axillary meristem fate and outgrowth.  Pairing the results from the FVT modeling and developmental timeseries, we find that M. gemmiparus has a faster nodal development when compared to M. guttatus and M. floribundus. Therefore, showing that in M. gemmiparus, growth rates of axillary meristems have been increased to support growth of a novel reproductive structure, formed from modified leaves and meristems that, in related species, would be used to form branches. Additionally, I sampled homologous nodes between all three species to perform a comparative evolutionary analysis to determine the genes that are differentially expressed and responsible for the modifications to existing structures to evolve the novel structure in M. gemmiparus.