During organ development, many key regulators have been identified in plant genomes, which play a conserved role among plant species to control the organ identities and/or determine the organ size and shape. It is intriguing whether these key regulators can acquire diverse function and be integrated into different molecular pathways among different species, giving rise to the immense diversity of organ forms in nature. In this study, we have characterized and cloned LATHYROIDES (LATH), a classical locus in pea, whose mutation displays pleiotropic alteration of lateral growth of organs and predominant effects on tendril and dorsal petal development. LATH encodes a WUSCHEL-related homeobox1 (WOX1) transcription factor, which has a conserved function in determining organ lateral growth among different plant species. Furthermore, we showed that LATH regulated the expression level of TENDRIL-LESS (TL), a key factor in the control of tendril development in compound leaf, and LATH genetically interacted with LOBED STANDARD (LST), a floral dorsal factor, to affect the dorsal petal identity. Thus, LATH plays multiple roles during organ development in pea: it maintains a conserved function controlling organ lateral outgrowth, and modulates organ identities in compound leaf and zygomorphic flower development, respectively. Our data indicated that a key regulator can play important roles in different aspects of organ development and dedicate to the complexity of the molecular mechanism in the control of organ development so as to create distinct organ forms in different species.