The enzyme Cu/Zn SOD is one of the first lines of defense for plants against stress induced, toxic superoxide radicals. Different structural forms of this enzyme are present in the two primary ryegrass species Lolium perenne and Lolium multiflorum. Recently it has been shown that a specific microRNA miR398 plays an important role in specifying the spatial and temporal expression patterns of Cu/Zn SOD mRNAs in Arabidopsis, Rice and Poplar. Future research aimed at identifying the regulatory mechanisms and potential utility of Cu/Zn SOD for species separation in the ryegrasses will be discussed.