Perennial wild red rice [Oryza rufipogon Griff.][ORYSA][CDFA list: B][Federal Noxious Weed] Photographs

[Back to Index]


SYNONYMS: common wild rice, brownbeard rice, Oryza aquatica Rosch., Oryza cubensis Eckman ex Gotoh & Okura, Oryza fatua Koen. ex Trin., Oryza glumipatula Steud., Oryza paraguayensis Wedd. ex E. Fourn, Oryza perennis Moench., Oryza sativa L. ssp. rufipogon (Griff). de Wet, Oryza sativa L. vars. abuensis G.Watt, coarctata G.Watt, fatua Prain, paraguayensis Franch. or Parodi, rubribarbis Desv., savannae Korn., sundensis Korn., Oryza sativa L. forma spontanea Rosh.

GENERAL DESCRIPTION: Variable perennial wild rice of shallow water, with floating or emergent leaves, to 4 m tall. Perennial wild red rice is a serious weed of rice fields in many regions of the world. Evidence suggests that cultivated rice (Oryza sativa L.) was originally derived from perennial wild red rice. Both species readily hybridize, and in Asia, hybridization and backcrossing between perennial wild red rice and cultivated rice has created a highly variable range of weedy perennial wild red rice types, including annual types, resulting in much taxonomic confusion. Annual types are often designated as biotypes of Oryza rufipogon in the literature. However, this distinction is controversial. The Federal and California noxious weed ratings pertain only to perennial wild red rice. Perennial wild red rice and hybrids have seed heads that shatter (shed seed) before maturity. Otherwise they are difficult to distinguish from commercial rice cultivars with red grains. Red-coated grains from weedy plants cannot be separated from commercial grains. After milling, white rice contaminated with perennial wild red rice appears dirty or requires additional milling, resulting in more broken grains and reducing the value of the crop. perennial wild red rice is sometimes used in rice breeding programs to impart certain characteristics to rice cultivars. Native to Asia.

SEEDLINGS: Sometimes more vigorous than commercial rice, but usually difficult to distinguish.

MATURE PLANT: Tufted to 20 cm in diameter, often with rhizomes. Lower stems spongy, floating, rooting at the nodes. Blades 10-80 cm long, 0.7-2.5 cm wide, often flat, glabrous, smooth to rough (scabrous), typically not as long or erect as cultivated rice. Margins minutely serrate. Sheaths open, often inflated in the lower portion. Ligules membranous, triangular to narrowly triangular, 9-25(45) mm long, usually split or ragged. Auricles lacking or 1-7 mm long, narrow, curved, glabrous or lined with long hairs to 2 mm long.

ROOTS and UNDERGROUND STRUCTURES: Roots fibrous, often with rhizomes.

back to top of page

SPIKELETS/FLORETS: Panicles 12-30 cm long, 1-7 cm wide, with loosely ascending branches. Spikelets early deciduous from above the vestigial glumes. Glumes reduced to minute ridges on the stalk. Florets 3, the lower 2 sterile and glume-like, the upper one fertile. Fertile floret +/- oblong, 7-11 mm long excluding lemma awn, ~ 2-3(4) mm wide. Lemma and palea green to yellowish, often dark red at apex, covered with stiff transparent hairs. Awn variable, stout, up to 11 cm long, often reddish. Anthers 6, 3.5-6 mm long, yellow or brown. Stigmas protruding, blackish-purple or brown. Grains red-brown, 5-7 mm long, 1.4-2 mm in diameter.

POSTSENESCENCE CHARACTERISTICS: Leaves usually turn brown as grains mature.

HABITAT: Rice fields, sites with shallow, standing or slow-running water.

DISTRIBUTION: At publication time, no known populations of perennial wild red rice have ever been found in California. Previous populations of perennial wild red rice hybrids in the Sacramento Valley have been eradicated.

PROPAGATION/PHENOLOGY: Reproduces by seed and vegetatively from rhizomes. Seeds fall near the parent plant or disperse to greater distances as rice seed contaminants, with human activities, water, soil movement, and possibly birds. Seeds do not survive ingestion by waterfowl. Seeds are typically dormant at maturity. Dormancy is partly due to the presence of inhibitors in the seed coat. Depending on the biotype and environment, seed may remain dormant and viable for up to 3 years or more under field conditions. Many seeds decay during long periods of flooded conditions. Germination typically occurs between 15-40º C (59-104º F). Seeds often germinate slightly sooner and at lower temperatures than commercial rice seeds. Some biotypes emerge from soil depths of up to 12 cm (~ 5 in).

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Planting perennial wild red rice-free certified seed may prevent new introductions of perennial wild red rice. Continuous flooding reduces perennial wild red rice seed survival and attracts ducks that feed on the grains.

SIMILAR SPECIES: Unlike perennial wild red rice, cultivated rice has persistent spikelets, white or yellow anthers 0.8-2.5 mm long, and grains 2.2-4 mm in diameter. Stigmas may be white, yellow, red, or blackish-purple.


Prevention and Control: This species is currently not known to occur in California. Prevention of its introduction and establishment is best achieved through using only certified seed. Additionally, any field equipment being transported into California from other states where red rice is a problem (i.e., Mississippi or Louisiana) should be thoroughly cleaned and inspected for red rice seed before being brought into the state. The potential for introduction and establishment may increase as the acreage of specialty market annual "red rice" increases which is very similar to the true perennial red rice. The perennial red rice may be discouraged by from establishing by spring tillage and also appears to require permanent water which is not a typical practice in California.

Duistermaat, Helena. 1987. A revision of Oryza (Gramineae) in Malesia and Australia. Blumea 32:157-193

back to top of page