Description from Flora of China
Annual or perennial, tufted or shortly rhizomatous. Culms erect or ascending. Leaf blades mainly cauline, broadly linear, flat; ligule membranous, sometimes long. Inflorescence a panicle, usually many-spiculate, often nodding, lower branches usually whorled, unbranched or sparsely branched, pedicels short. Spikelets with 3 florets, 2 lower florets reduced, sterile, upper floret fertile, strongly laterally compressed, disarticulating below sterile lemmas, persistent in cultivated species; glumes vestigial, remaining after disarticulation as a shallow lobed frill at pedicel apex; sterile florets reduced to 2 narrow lemmas at base of fertile floret; fertile lemma boat-shaped, keeled, leathery, closely papillose, sometimes spinulose, infrequently smooth, prominently 5-veined, apex awnless to long awned; awn straight; palea resembling lemma but narrower, 3-veined, apex beaked. Stamens 6. Caryopsis variable in shape, embryo 1/4 length of caryopsis, hilum linear, as long as caryopsis. x = 12.
Oryza includes rice, O. sativa, the staple cereal crop throughout most of S China and tropical Asia.
The narrow scales at the base of the fertile floret are sometimes regarded as glumes rather than sterile lemmas, the shallow frill at the pedicel apex being then regarded simply as pedicel tissue. However, aberrant forms of Oryza sativa have been reported with one or more of the basal scales well developed and even enclosing a grain, which appears to support their derivation from lemmas.
Oryza latifolia Desvaux is a species from Central and South America which has been reported in Beijing.
Twenty-four species: warm parts of Africa, Asia, Australia, and Central and South America; five species (two introduced) in China.