Inference of the ancestral karyotypes and chromosome evolutionary trajectories of four Oleaceae species. A, The evolutionary trajectories of the ancestral chromosomes in the ancestor before the diversification of Oleaceae. ECH, core-eudicot common hexaploidization; OCH, Oleaceae common hexaploidization; ORT, Oleaceae recent tetraploidization. G1-G7, 7 ancestral eudicot chromosomes. O, P and Q represent the three subgenomes generated from the OCH event. B, Reconstruction of the ancestral karyotypes of the Oleaceae. AOK, ancestral Oleaceae karyotype; AEK, ancestral eudicot karyotype. The arrows in the AOK and post-ORT karyotypes represent the chromosome fusion events.