5.01 ORYZA L.
Mary E. Barkworth
Edward E. Terrell

Plants annual or perennial; usually aquatic, rooted and emergent or floating, sometimes terrestrial; rhizomatous and/or cespitose; synoecious. Culms to 3.3(5) m, erect, decumbent, or prostrate, sometimes rooting at the lower nodes, aerenchymatous, emergent or immersed, branched or unbranched. Leaves cauline and basal; sheaths open, lower sheaths often slightly inflated, upper sheaths not inflated; auricles usually present; ligules membranous, often veined; pseudopetioles absent; blades linear to narrowly lanceolate, flat, margins smooth or scabridulous. Inflorescences terminal panicles; disarticulation above the glumes, beneath the sterile florets in wild taxa, spikelets of cultivated taxa not disarticulating. Spikelets bisexual, laterally compressed, with 3 florets, lower 2 florets sterile, terminal floret functional. Glumes absent or reduced to lobes at the pedicel apices; sterile florets glumelike, 1.2–10 mm, 1/8–1/2(9/10) as long as the spikelets, linear or subulate to narrowly ovate, coriaceous, 1-veined, acute to acuminate; functional florets: calluses usually inconspicuous and flat to rounded, sometimes conspicuous and stipelike, glabrous; lemmas coriaceous or indurate, with vertical rows of tubercles separated by longitudinal furrows, 5-veined, keeled, margins clasping the margins of the paleas, apices obtuse or acute to acuminate, awned or unawned; paleas with surfaces similar to the lemmas, 3-veined, unawned; lodicules 2; anthers 6; styles 2, bases fused or not, stigmas laterally exserted, plumose. Caryopses laterally compressed; embryos usually 1/4–1/3 as long as the caryopses; hila linear. x = 12. Name from the Greek oryza, ‘rice’.

Oryza is a tropical and subtropical genus of about 20 species that grow in shallow water, swamps, and marshes in seasonally inundated areas, or along streams, rivers, or lake edges. Oryza sativa (rice) is one of the three most economically valuable cereals, and constitutes a major portion of the diet for half of the world’s population. In the Flora region, O. sativa is cultivated and several weedy forms have become established. These are thought to be derived from introgression between O. sativa and O. rufipogon and O. punctata. The latter two species and O. longistaminata are included here because of the threat they pose to cultivated rice.

Spikelets of Oryza have sometimes been interpreted as comprising one functional and two sterile florets with two highly reduced glumes (Duistermaat 1987), sometimes as comprising a single floret, subtended by two glumes borne on a bilobed pedicel (Terrell et al. 2001). Molecular developmental studies (Komatsu et al. 2003) show that the former interpretation is correct.

SELECTED REFERENCES Duistermaat, H. 1987. A revision of Oryza (Gramineae) in Malesia and Australia. Blumea 32:157–193; Komatsu, M., A. Chujo, Y. Nagato, K. Shimamoto, and J. Kyozuka. 2003. FRIZZY PANICLE is required to prevent the formation of axillary meristems and to establish floral meristem identity in rice spikelets. Development 130:3841–3850; Launert, E. 1971. Oryza L. Pp. 31–36 in A. Fernande, E. Launert, and H. Wild (eds.). Flora Zambesiaca, vol. 101. Crown Agents for Oversea Governments and Administrations, London, England. 152 pp.; Londo, J.P., Y.-C. Chiang, K.-H. Hung, T.-Y. Chiang, and B.A. Schaal. 2006. Phylogeography of Asian wild rice, Oryza rufipogon, reveals multiple independent domestications of cultivated rice, Oryza sativa. Proc. Natl. Acad. Sci. U.S.A. [PNAS] 103(25):9578–9583; Lu, B.-R., E.B. Naredo, A.B. Juliano, and M.T. Jackson. 2000. Preliminary studies on taxonomy and biosystematics of the AA genome Oryza species (Poaceae). Pp. 51–58 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. CSIRO Publishing, Collingwood, Victoria, Australia. 406 pp.; Terrell, E.E., P.M. Peterson and W.P. Wergin. 2001. Epidermal features and spikelet micromorphology in Oryza and related genera (Poaceae: Oryzeae). Smithsonian Contr. Bot. 91. 50 pp.; Vaughan, D.A. 1989. The Genus Oryza L.–Current Status of Taxonomy. International Rice Research Institute Research Paper Series 138. International Rice Research Institute, Los Baños, Laguna, Philippines. 21 pp.


For an interactive dichotomous key, click here; for an interactive, multientry key, click here.


1. Ligules truncate to rounded, 1.5–10 mm long; sterile florets 1.2–2 mm long; disarticulation scar centric or slightly eccentric ... O. punctata
1. Ligules acute, 4–45 mm long; sterile florets 1.3–10 mm long; disarticulation scar lateral ... 2
2. Anthers 1–2.5 mm long; spikelets persistent; lemmas usually unawned, plants not rhizomatous; auricles absent or to 5 mm long; blades 5–20 mm wide ... O. sativa
2. Anthers 3.5–7.4 mm long; spikelets deciduous; lemmas awned; plants usually rhizomatous; auricles absent or to 15 mm long; blades 7–50 mm wide ... 3
3. Caryopses 5–7 mm long; lemma-awn junctions purplish, pubescent; lemma awns 4–16 cm long; plants cespitose or rhizomatous; auricles absent or to 7 mm long ... O. rufipogon
3. Caryopses 7.5–8.5 mm long; lemma-awn junctions similar in color to the lemmas, glabrous; lemma awns 2.6–8 cm long; plants strongly rhizomatous; auricles present, to 15 mm long ... O. longistaminata



1. Oryza longistaminata A. Chev. & Roehr.
Longstamen Rice

Plants perennial; extensively rhizomatous. Culms to 2+ m tall, to 25+ mm thick at the base, soft and spongy, erect or decumbent, sometimes floating, rooting at the lower nodes. Sheaths shorter or nearly as long as the internodes, smooth, glabrous; auricles to 15 mm; ligules 15–45 mm, acute, often splitting; blades to 45 cm long, 10–50 mm wide, linear-lanceolate to narrowly elliptic, glabrous, smooth or scabrous abaxially, scabrous adaxially, acute or 2-cleft. Panicles (16)20–30(40) cm long, 2.5–8 cm wide, exserted; branches 7.5–15 cm, ascending; pedicels 0.5–4(7) mm. Spikelets 7–9 mm long, 2–3 mm wide, narrowly oblong, deciduous, obliquely articulated with the pedicel, disarticulation scar lateral. Sterile florets 2–4 mm, 1/5–3/5 as long as the spikelets, sometimes trilobed, lateral lobes shorter than the central lobe. Functional florets: lemmas 7–9 mm long, 1.8–2.5 mm wide, narrowly elliptic, scabrous to hispid over the veins, awned, lemma-awn junctions glabrous, colored as the lemmas, awns (2.6)3.5–8 cm; paleas usually slightly shorter than the lemmas, narrower, acute or tapering; anthers 5–7 mm. Caryopses 7.5–8.5 mm, oblong, light brown, glossy. Haplome A. 2n = 24.

Oryza longistaminata is native to Africa; it has not yet been found in North America. It is included here because its establishment in North America would seriously impact North American agriculture. The U.S. Department of Agriculture considers it a noxious weed; plants found growing within the United States should be promptly reported to that agency.

In its native range, Oryza longistaminata grows in swampy areas, pond and lake edges, irrigation canals, and streams and rivers in areas that are permanently wet or seasonally dry.



2. Oryza rufipogon Griff.
Red Rice, Brownbeard Rice

Plants annual or perennial; cespitose, sometimes rhizom-atous, rhizomes elongated. Culms 0.6–3.3(5) m tall, 6–15 mm thick, decumbent or pros-trate, rooting and branching at both the lower and submerged upper nodes. Sheaths smooth, glabrous; auricles sometimes present, 1–7 mm, erect; ligules 7–45 mm, acute, finely splitting; blades 10–80 cm long, 7–24 mm wide, smooth or scabrous. Panicles 12–30 cm long, 1–7 cm wide; branches 2.5–12(20) cm, ascending or divergent; pedicels 1–3 mm. Spikelets 4.5–11 mm long, 1.6–3.5 mm wide, oblong or elliptic, deciduous, obliquely articulated with the pedicel, disarticulation scar lateral. Sterile florets 1.3–7 mm long, 1/4–1/2(3/4) as long as the spikelets, 0.3–0.7 mm wide, acute. Functional florets: lemmas 6–11 mm long, 1.4–2.3 mm wide, hispid, apices beaked, beaks to 1 mm, straight or curved, lemma-awn junctions marked by a purplish, pubescent constriction, awns 4–11(16) cm; paleas 0.5–1.2 mm wide, acuminate to awned to 2.3 mm; anthers 3.5–7.4 mm, yellow or brown. Caryopses 5–7 mm long, 2.2–2.7 mm wide, broadly elliptic or oblong, reddish-brown to dark red; embryos 1–1.5 mm. Haplome A. 2n = 24.

Oryza rufipogon is native to southeast Asia and Australia, where it grows in shallow, standing or slow-moving water, along irrigation canals, and as a weed in rice fields. It is the ancestor of O. sativa (Londo et al. 2006). The vernacular name ‘Red Rice’ is used to refer to O. rufipogon, O. punctata, and weedy forms of O. sativa, some of which are probably derivatives of introgression from the first two species.

Oryza rufipogon is a weedy taxon that hybridizes readily with O. sativa, forming partially fertile hybrids. This makes it a serious threat to rice growers. Some of the known populations have been eradicated, for instance those in Everglades National Park, Miami-Dade County, Florida, and in the Sacramento Valley, California. Nevertheless, weedy red rice has become an increasingly serious problem in rice fields throughout rice-growing regions of the world, including the contiguous United States, probably through the presence of fertile seed in commercial seed.



3. Oryza punctata Kotschy ex Steud.
Red Rice

Plants annual or perennial; cespitose. Culms 0.6–1.2 m tall, usually 4 mm or more thick, erect, branched, spongy. Sheaths smooth, glabrous; auricles present; ligules 1.5–10 mm, truncate to rounded, whitish, tending to split at maturity; blades 20–60 cm long, 10–30 mm wide, linear, usually scabrous, rarely glaucous. Panicles 20–35 cm long, 3–17 cm wide, loose; branches to 20 cm, divergent; pedicels 2–5 mm. Spikelets 4.6–9.2 mm long, 2–2.5 mm wide, asymmetrically elliptic-oblong to broadly oblong, deciduous, horizontally or slightly obliquely articulated with the pedicels, disarticulation scar centric or slightly eccentric. Sterile florets 1.2–2 mm, 1/5–2/5 as long as the spikelets, acute. Functional florets: lemmas 4.6–9.2 mm long, 1.9–2.6 mm wide (about 2.5 times longer than wide), hispid, awned, awns (1)2–7.5 cm; paleas usually slightly shorter than the lemmas, narrower, acute or tapering; anthers 1.5–3.2 mm. Caryopses 4–4.8 mm long, 1.5–1.8 mm wide, oblong, light brown. Haplomes B, BC. 2n = 24, 48.

Oryza punctata is an African grass that is not established in North America. It is considered a noxious weed by the U.S. Department of Agriculture; if any populations are found in the United States, that agency should be notified. It has two morphological types. The tetraploid race is perennial, with spikelets to 5.5 mm long and at least 2.3 mm wide. It grows in semi-open or shaded forest habitats, in swampy areas, water holes, pools, and river areas that flood to 1 m in depth. The diploid race is annual, with spikelets 5.5 mm or more long and at most 2.3 mm wide. It grows in open to semi-open forest margins, grasslands, and thickets, scrub, and open bush, in swampy areas, water holes, pools, and river areas that flood to 1 m in depth.

The vernacular name ‘Red Rice’ is used to refer to Oryza rufipogon, O. punctata, and weedy forms of O. sativa, some of which may be the result of introgression from the first two species.



4. Oryza sativa L.

Plants usually annual, some-times perennial; cespitose, not rhizomatous. Culms 0.3–2 m tall, 4–20 mm thick, erect or ascending, branching at the base, usually rooting at both the lower and submerged upper nodes. Sheaths smooth, glabrous, lowest sheaths usually longer than the internodes, upper sheaths shorter than the internodes; auricles often present, 1–5 mm; ligules (4)10–36 mm, acute; blades 20–70 cm long, 5–20 mm wide, glabrous, sometimes scabrous. Panicles 10–50 cm long, 1–8 cm wide, often nodding; branches 2–13 cm, ascending or divergent; pedicels 1–7 mm. Spikelets 6–11 mm long, 2.5–4 mm wide, broadly elliptic, sometimes with obvious rows of white papillae, persistent, obliquely articulated with the pedicels. Sterile florets 1.5–3(10) mm long, 1/4–1/2(9/10) as long as the spikelets, 0.5–1.5 mm wide. Functional florets: lemmas 6–11 mm long, 2–3 mm wide, glabrous or with stiff hairs to 1.5 mm, apices beaked, beaks 0.3–1(2) mm, rigid, usually unawned, sometimes awned, awns to 6(15) cm; paleas 1–1.7 mm wide, acute to acuminate or mucronate to 0.5 mm; anthers 1–2.5 mm, white or yellow; styles white, yellow, red, or blackish-purple. Caryopses 4.5–8 mm long, 2–3.5 mm wide, broadly elliptic or broadly oblong, brown, tan, or white; embryos 1.4–1.7 mm. Haplome A. 2n = 24.

Oryza sativa is cultivated in California, Arkansas, Texas, Louisiana, Mississippi, and Florida and is sometimes found as an adventive in moist or wet places, particularly in the southeastern United States, but it is not established in the Flora region. It used to be extensively cultivated in the Carolinas and Georgia, but no rice plantations are currently known to be in operation in those states. Many cultivars have been developed; there is considerable morphological, as well as ecological, variability in the cultivated crop.