Plant secondary cell walls play a vital role in providing structure, protection, and mechanical support, and collectively represent a major carbon sink within the plant. The HD-ZIP III transcription factor REVOLUTA (REV) is a key regulator of vascular development and secondary cell wall formation in dicot plants, but its role in grasses remains poorly understood. Here we investigate the function of REV in the model cereal grass, Brachypodium distachyon, using two mutant alleles, rev-1 and rev-2, which result in a premature stop codon in the START domain and an amino acid substitution bordering the MEKHLA domain, respectively. We are using these mutants to visualize the effects on secondary cell wall thickening in stems by comparing them to wild-type plants. Histological analysis and phloroglucinol staining were used to visualize and measure cell wall thickness in multiple cell types, including mestome, interfascicular, and xylem cells. Preliminary results indicate that both mutants have a decrease in lignin and secondary cell wall thickness of interfascicular cells. Additionally, rev-1 has a significant increase in vascular bundle formation. These findings suggest that REV plays a conserved role in regulating secondary cell wall development and has a pleiotropic nature. Ongoing work includes the generation of additional mutant alleles in a reporter line to better understand REV’s role in regulating secondary cell wall development.