Auxin regulates the initiation and radial position of plant lateral organs. This study shows that auxin is essential for and sufficient to induce organogenesis in both the vegetative tomato meristem and the Arabidopsis inflorescence meristem. Inhibition of polar auxin transport blocks leaf formation, resulting in pinlike structures with an intact meristem. Application of auxin restores leaf formation, indicating that auxin determines the radial position and size of lateral organs but not their apical-basal position or identity. Auxin treatment at specific positions in the meristem induces leaf primordia at the radial position, while organ formation occurs at a fixed distance from the meristem summit in the apical-basal dimension. Local application of auxin to the Arabidopsis pin1-1 mutant inflorescence apices induces flower primordia, showing that auxin can trigger organogenesis without determining organ identity. The results suggest that auxin plays a central role in organ initiation and positioning, with its effects dependent on the radial position and concentration. Auxin transport is required for lateral organ formation, and its inhibition leads to the accumulation or depletion of auxin in the meristem. The study highlights the role of auxin in radial patterning and the interaction between auxin transport and vascular development in determining phyllotaxis.Auxin regulates the initiation and radial position of plant lateral organs. This study shows that auxin is essential for and sufficient to induce organogenesis in both the vegetative tomato meristem and the Arabidopsis inflorescence meristem. Inhibition of polar auxin transport blocks leaf formation, resulting in pinlike structures with an intact meristem. Application of auxin restores leaf formation, indicating that auxin determines the radial position and size of lateral organs but not their apical-basal position or identity. Auxin treatment at specific positions in the meristem induces leaf primordia at the radial position, while organ formation occurs at a fixed distance from the meristem summit in the apical-basal dimension. Local application of auxin to the Arabidopsis pin1-1 mutant inflorescence apices induces flower primordia, showing that auxin can trigger organogenesis without determining organ identity. The results suggest that auxin plays a central role in organ initiation and positioning, with its effects dependent on the radial position and concentration. Auxin transport is required for lateral organ formation, and its inhibition leads to the accumulation or depletion of auxin in the meristem. The study highlights the role of auxin in radial patterning and the interaction between auxin transport and vascular development in determining phyllotaxis.