AbstractThe LFY transcription factor gene family are important in the promotion of cell proliferation and floral development. Understanding their evolution offers an insight into floral development in plant evolution. Though a promiscuous transition intermediate and a gene duplication event within the LFY family had been identified previously, the early evolutionary path of this family remained elusive. Here, we reconstructed the LFY family phylogeny using maximum-likelihood and Bayesian inference methods incorporating LFY genes from all major lineages of streptophytes. The well-resolved phylogeny unveiled a high-confidence duplication event before the functional divergence of types I and II LFY genes in the ancestry of liverworts, mosses and tracheophytes, supporting sub-functionalization of an ancestral promiscuous gene. The identification of promiscuous genes in Osmunda suggested promiscuous LFY genes experienced an ancient transient duplication. Genomic synteny comparisons demonstrated a deep genomic positional conservation of LFY genes and an ancestral lineage-specific transposition activity in grasses.