Plants annual, forming tufts or small clumps. Flowering stems 50–160 cm long, erect, usually unbranched, glabrous. Leaf sheaths glabrous or sparsely hairy, open for most of their length, the ligule membranous, 2‑lobed. Leaf blades 20–50 cm long, 5–18 mm wide, flat at maturity, sometimes somewhat thickened and spongy at the base, the base often with a pair of short auricles, glabrous but often somewhat roughened along the midrib and margins. Inflorescences open panicles with loosely ascending to spreading or slightly drooping racemose branches. Spikelets numerous, short‑stalked, strongly flattened, with 2 sterile lemmas below the 1 perfect floret, these appearing glumelike. True glumes reduced to a minute, cuplike structure at the spikelet base. Sterile, glumelike lemmas 1.5–3.0 mm long, similar in size and appearance, narrowly lanceolate, sharply pointed at the tip, faintly 1‑nerved, glabrous. Fertile lemma 7–10 mm long, strongly keeled, oblong‑obovate, pointed at the tip, awnless or the awn 1–5 mm long, the surface glabrous, pebbled, or hairy, with a fine network of wrinkles, 5‑nerved. Palea similar in size and appearance to the lemma, but somewhat narrower and with only 2 marginal nerves. Stamens 6. Fruits 6.5–7.0 mm long, elliptic in outline, white or nearly so, enclosed by the persistent lemma and palea, which harden at maturity. 2n=24. June–September.

Introduced, escaped sporadically from cultivation in the Mississippi Lowlands Division and in Lincoln and Marion Counties (widely cultivated in warmer parts of the world, escaping sporadically in the southern U.S.). Roadside depressions and ditches.

Rice is among the world’s most important crop plants, with uses ranging from the well‑known edible grain to the use of fibers for paper manufacture. In parts of Asia it is used for distillation of alcohol. The cultivated taxon was developed from plants probably native to Asia. Numerous cultivars of three subspecies often are recognized in the literature on the species’ domestication (Tucker, 1988). Cultivation in Missouri is mostly restricted to portions of the Mississippi Lowlands and the Mississippi River floodplain farther north. Hulls (persistent lemmas and paleas) from the Missouri rice crop have been used as a component of potting mix for commercial production of ornamental shrubs and trees. The rice fields are an important habitat for a variety of bird species when flooded in the early spring. They also provide habitats for various amphibians and other small aquatic fauna, as well as an array of weedy aquatic plant species. Escaped plants of rice in Missouri probably do not persist for very long in the wild.