Together with ARGOS and ARL, regulates organ growth and final organ size. Promotes both cell expansion and proliferation-dependent organ growth, in an ANT-dependent manner. Mostly expressed in flowers, and, to a lower extent, in leaves and cotyledons. Detected in leaf primordia. In leaves, present in the blade and the petiole, especially at the dispersed meristematic regions and the leaf margin. Accumulates in floral organs. Induced by ethylene but repressed by abscisic acid (ABA) and epi-brassinolide (epi-BL) treatments. The OSR domain is sufficient to promote organ growth. When associated with ARGOS disruption, reduction in organ size. Belongs to the plant organ size related (OSR) protein family.