4. Oryza sativa Linnaeus, Sp. Pl. 1: 333. 1753.
Oryza formosana Masamune & Suzuki; O. sativa var. formosana (Masamune & Suzuki) Yeh & Henderson.
Annual, aquatic, tufted. Culms erect, rooting at lower submerged nodes, 0.5–1.5 m tall. Leaf sheaths slightly inflated below, upper sheaths tight, glabrous, auricles falcate, ciliate; leaf blades 25–60 × 0.5–2 cm, glabrous, smooth or scabrid on both sides, margins scabrid, apex acuminate; ligule 10–40 mm. Panicle loosely contracted, up to 30 cm, nodding at maturity; branches 1–3 at lowest node, longest 2–12 cm, axils bearded or glabrous. Spikelets oblong to oblong-lanceolate, 7–10 mm, length 2–3.5 times width, persistent; sterile lemmas lanceolate, 1.5–4 mm, apex acuminate; fertile lemma papillose, spinulose, apex acuminate; awn very variable, slender or stout, up to 60 mm or more, scaberulous, sometimes absent. Anthers 1–3 mm. Caryopsis ovate or elliptic to cylindrical, 5–7 mm, whitish yellow to brown or blackish. 2n = 24.
Cultivated, mainly in flooded fields. Throughout most of China [domesticated in SE Asia].
This is the staple cereal rice, widely cultivated in tropical and warm-temperate parts of the world, and with many different cultivated races. It has the AA genome, and where Oryza rufipogon occurs as a weed in rice fields, intermediates may occur.