Oryza rufipogon

Name and classification

Oryza rufipogon Griff.
Family Poaceae, Tribe Oryzeae

Common names

red rice

Disseminule

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

Description

Disseminule (floret with 2 sterile lemmas) oblong or elliptic, ca. 6–11 mm long, 1.6–3.6 mm wide; callus smooth; disarticulation scar lateral. Sterile lemmas similar, glume-like, linear, glabrous, 1.3–7 mm long, 0.3–0.7 mm wide. Rachilla elongated below fertile lemma. Fertile lemma and palea strongly laterally compressed, keeled, cartilaginous, surface scaberulous and tuberculate in a grid pattern. Lemma 6–11 mm long, 1.4–2.3 mm wide, 5-nerved; its margins inrolled, interlocking palea margins; with apical awn to 12 cm long, straight, antrorsely barbed. Caryopsis broadly elliptic or oblong, 5–7 mm long, 2.2–2.7 mm wide, laterally compressed, reddish; hilum linear, as long as caryopsis.

Identification considerations

The wild red rices (Oryza 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 disseminules 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.

disseminules in side view

disseminules in side view

disseminule

disseminule

disseminules with intact awns

disseminules with intact awns

detail of fertile lemma surface

detail of fertile lemma surface

caryopses in side view

caryopses in side view

A, fertile floret with 2 attached sterile lemmas; B, caryopsis in side view showing embryo; drawing by Lynda E. Chandler

A, fertile floret with 2 attached sterile lemmas; B, caryopsis in side view showing embryo; drawing by Lynda E. Chandler