Arabidopsis leaf morphology is determined by the coordinated action of cell division and elongation. Of all the hormones that control leaf shape, the brassinosteroids (BRs) are active components in this process. BRs are a group of plant-originated steroidal compounds that induce growth along the long axes of organs. Here, we report the isolation and characterization of a novel mutant, short root and dwarfism (srd). Its dwarf phenotype includes round and curled leaves, reduced fertility, and short hypocotyls in the light and dark. Dwarfism in the aerial portions and a short-root morphology are not rescued by exogenous application of BRs, suggesting that srd is not impaired in BR metabolic pathways. Anatomical analysis revealed that srd roots are much shorter and thicker than the wild type due to additional layers of cortical cells. A lack of cell elongation but an increase in division results in these short but horizontally swollen roots. A double mutant srd/brit-5 also displays the short-root phenotype, implying that srd is epistatic to brito Cloning and further characterization of SRD should provide additional information about its role in the determination of leaf shape and root elongation.