In plants, serine/arginine-rich splicing factors (SRSFs) play an essential role in pre-mRNA splicing, influencing growth and stress response. The present study investigated the evolution and diversification of SR proteins in plants by phylogenetic analysis. First, we identified 1650 SR proteins from 132 plant species. Large-scale phylogenetic analysis divided these SR proteins into nine subfamilies: SR, RS, SC, SCL, RSZ, RS2Z, SR45, SR45a, and a newly discovered RSZ-like subfamily. The analysis also suggested that SR proteins of animals and plants originated from an ancient SR gene of a common ancestor of eukaryotes and showed that RSZ-like subfamily diverged in fern. We also found the presence of the newly discovered RSZ-like subfamily in ferns, gymnosperms, and angiosperms as a sister group of SR45 and SR45a, indicating a common ancestor. In addition, we detected deletion of the N-terminal RS domain in a few members of SR45 and SR45a of plants. These findings provide novel insights into the phylogeny of the SR gene family in plants, emphasizing their crucial function as a splicing factor.