Inside the genus Oryza, species can be divided by their genomes types. They include the diploid (2n = 24) AA of cultivated rice and their relatives, BB, CC, EE, FF and GG as well as the tetraploid (4n = 48) BBCC, CCDD, HHJJ, HHKK and KKLL. Species of the same genome type cross easily, while hybridizing different types requires techniques like embryo rescue.[8][9]