Oryza is situated in tribe Oryzeae, which is characterized morphologically by its single-flowered spikelets whose glumes are almost completely suppressed. In Oryza, two sterile lemma simulate glumes. The tribe Oryzeae is in subfamily Ehrhartoideae,[6] a group of Poaceae tribes with certain features of internal leaf anatomy in common. The most distinctive leaf characteristics of this subfamily are the arm cells and fusoid cells found in their leaves.[7][verification needed]
One species, Asian rice (O. sativa), provides 20% of global grain and is a food crop of major global importance. The species are divided into two subgroups within the genus.
Species
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]
Over 300 names have been proposed for species, subspecies, and other infraspecific taxa within the genus. Published sources disagree as to how many of these should be recognized as distinct species. The following follows the World Checklist maintained by Kew Garden in London.[2]
