All life arises from a single cell. Sometimes, many cells are created from one and allow for complex life. In complex organisms, cell activity must be carefully orchestrated to initiate and mature organs of the correct placement, size and shape. Arabidopsis leaves offer a unique opportunity to study these developmental processes at the cellular level. From early initiation, leaves are amenable to repetitive imaging on a confocal microscope and plant cells do not move. Thus, the growth rates and geometric properties of cells in the developing lamina can be tracked over time. In this work, I have increased the resolution at which we understand cellular changes in developing WT and jaw-D leaves. jaw-D leaves ripple and wave while WT leaves are flat. The jaw-D mutant was discovered in a screen and results from the overexpression of microRNA319 (miR319) at its endogenous locus (Palatnik et al., 2003). miR319 targets mRNAs of members of the class II TCP transcription factor family for degradation (Palatnik et al., 2003, 2007). TCPs have been shown to target genes associated with differentiation and cell division (Efroni et al., 2008; Koyama et al., 2007; Schommer et al., 2008, 2014; Sun et al., 2017; Bresso et al., 2018). Therefore, it is hypothesized that proper spatial expression of miR319 is necessary to create simple, flat leaves in WT by modulating tissue growth and development (Alvarez et al., 2016; Nag et al., 2009; Challa et al., 2019). My work sheds new light on how miR319 contributes to leaf shape through spatial regulation of cell growth, division and differentiation. Future work from our lab will investigate the spatial relationships between miR319 and other developmental gene regulatory networks and their resultant tissue patterning effects.