We report a recessive mutation of rice, aberrant panicle organization 1 (apo1), which severely affects inflorescence architecture, floral organ identity, and leaf production rate. In the wild-type inflorescence, the main-axis meristem aborts after forming 10-12 primary branch primordia. However, in apo1, the main-axis meristem was converted to a spikelet meristem after producing a small number of branch primordia. In addition, the branch meristems in apo1 became spikelet meristems earlier than in wild type. Therefore, in the inflorescence, the apo1 mutation caused the precocious conversion of the meristem identity. In the apo1 flower, lodicules were increased at the expense of stamens, and carpels were formed indeterminately by the loss of meristem determinacy. Vegetative development is also affected in the apo1. Leaves were formed rapidly throughout the vegetative phase, indicating that APO1 is also involved in temporal regulation of leaf production. These phenotypes suggest that the APO1 plays an important role in the temporal regulation of both vegetative and reproductive development.