Oryza rufipogon Griff.

Family: Poaceae,  Tribe: Oryzeae

Common names:  red rice

Disseminule 

Fertile floret with two glume-like sterile florets; disarticulation above the glumes (below the glume-like sterile lemmas).

Description

Disseminule (floret with 2 sterile lemmas) oblong or elliptic, ca. 7-11 mm long, 2-3.6 mm wide. Callus smooth, oblique. Sterile lemmas similar, glume-like, linear, glabrous, 1.2-4 mm long. Rachilla elongated below fertile lemma. Fertile lemma and palea strongly laterally compressed, keeled, cartilaginous, surface scaberulous and tuberculate in a grid pattern; lemma 5-nerved, its margins inrolled, interlocking palea margins, lemma with apical awn to 12 cm long, straight, antrorsely barbed. Caryopsis lanceolate or oblong, 5-7 mm long, laterally compressed, reddish, hilum linear, as long as caryopsis.

Identification remarks

The wild red rices (O. longistaminata, O. punctata and O. rufipogon) can be distinguished from O. sativa L. (cultivated rice) by their red caryopses, although it may be difficult to differentiate the wild red caryopses from commercial rice cultivars with red grains.

The spikelets of O. rufipogon and O. longistaminata are difficult to differentiate morphologically. However, the two species are distinct geographically; O. rufipogon is not found in Africa, while O. longistaminata is found mostly in Africa.

Similar species

Oryza longistaminata A. Cheval. & Roehr.

Oryza punctata Kotschy ex Steudel

Distribution

Tropical Asia from the Indian subcontinent to Southeast Asia and Australia; tropical South America, Central America, Mexico, United States.

Native to Asia.

Habitat

Sites with shallow, standing or slow-running water, rice fields.

General information

Oryza rufipogon is thought to be the wild progenitor of O. sativa (cultivated rice – the important worldwide food crop). The two species are similar (vegetatively they are identical) and hybridize freely. The evolution of O. sativa is characterized as having started as a wild perennial, then becoming a wild annual, and then a cultivated annual. It has been suggested that the existence of “pure” forms of O. rufipogon is only conceptual, because of the continual crossing among cultivated and wild rice types, resulting in a conglomerate of hybrids. Thus confusion exists taxonomically about the delineation of species. This may be why some authors consider the name O. rufipogon to be that of a perennial grass with rhizomes, while others say it is an annual.

Oryza rufipogon is an aggressive weed of rice in many regions of world. It (and the other wild red rices) compete with and reduce the yield of cultivated rice. Moreover, they are considered weeds because the spikelet shatters (disarticulates easily), the seeds have dormancy, and the grain coat is red. Dispersal of red rice is most commonly as a contaminant in ricestock. This contamination requires additional milling to remove the red grains, increasing the number of broken grains, thus lessening the quality (price) of the product.

Florets in side view

Floret

Florets with intact awns

Detail of floret surface

Caryopses in side view

A, Floret; B, caryopsis in side view showing embryo

drawing by Lynda E. Chandler