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Auxin Response Factors (ARFs) make up a plant-specific transcription factor family that mainly couples perception of the phytohormone, auxin, and gene expression programs and plays an important and multi-faceted role during plant growth and development. Lemongrass (<i>Cymbopogon flexuosus</i>) is a representative Cymbopogon species widely used in gardening, beverages, fragrances, traditional medicine, and heavy metal phytoremediation. Biomass yield is an important trait for several agro-economic purposes of lemongrass, such as landscaping, essential oil production, and phytoremediation. Therefore, we performed gene mining of <i>CfARFs</i> and identified 26 and 27 CfARF-encoding genes in each of the haplotype genomes of lemongrass, respectively. Phylogenetic and domain architecture analyses showed that CfARFs can be divided into four groups, among which groups 1, 2, and 3 correspond to activator, repressor, and ETTN-like ARFs, respectively. To identify the CfARFs that may play major roles during the growth of lemongrass plants, RNA-seq was performed on three tissues (leaf, stem, and root) and four developmental stages (3-leaf, 4-leaf, 5-leaf. and mature stages). The expression profiling of <i>CfARFs</i> identified several highly expressed activator and repressor <i>CfARFs</i> and three <i>CfARFs</i> (<i>CfARF3</i>, <i>18</i>, and <i>35</i>) with gradually increased levels during leaf growth. Haplotype-resolved transcriptome analysis revealed that biallelic expression dominance is frequent among <i>CfARFs</i> and contributes to their gene expression patterns. In addition, co-expression network analysis identified the modules enriched with <i>CfARFs</i>. By establishing orthologous relationships among <i>CfARFs</i>, sorghum <i>ARFs</i>, and maize <i>ARFs</i>, we showed that <i>CfARFs</i> were mainly expanded by whole-genome duplications, and that the duplicated <i>CfARFs</i> might have been divergent due to differential expression and variations in domains and motifs. Our work provides a detailed catalog of <i>CfARFs</i> in lemongrass, representing a first step toward characterizing <i>CfARF</i> functions, and may be useful in molecular breeding to enhance lemongrass plant growth.