Double-flowered cultivars are generally considered more attractive than single-flowered varieties in ornamental plants. The AP2/ERF transcription factors superfamily plays pivotal roles in plant development, including floral organ formation. Here, a total of 248 AP2/ERF genes were identified in the genome of L. speciosa, and these genes were unevenly distributed on the 24 chromosomes. Phylogenetic analysis classified LsAP2/ERF genes into five distinct groups; the ERF subfamily was the largest, whereas the AP2 subfamily was associated with floral development. Gene duplication events contributed to the expansion of LsAP2/ERF family members, with segmental duplication identified as the primary contributor. Promoter cis-element analysis revealed an abundance of light-responsive and hormone-responsive elements. Spatiotemporal expression profiling showed that core AP2 subfamily members (LsAP2/ERF4/9/10/13/219) exhibited distinct expression patterns during flower bud development. Moreover, heterologous overexpression of LsAP2/ERF10 in tobacco resulted in transgenic lines with altered petal morphology, supporting its potential functional involvement in floral development. This study provides comprehensive characterization of the AP2/ERF family in L. speciosa, laying the foundation for elucidating its molecular mechanisms in floral morphogenesis.