Plants annual. Culms 40-120 cm, erect, densely
tufted; nodes glabrous. Sheaths glabrous; ligules absent;
blades lax or drooping, 7-20 cm long, 4-12 mm wide, mostly glabrous.
Panicles 8-17(25) cm, lax, horizontal to strongly drooping, rachis nodes
hispid, hairs to 4 mm, papillose-based, internodes glabrous; primary branches
to 5 cm, appressed to the rachises, mostly simple, glabrous or sparsely
hispid, hairs to 3.5 mm, papillose-based, particularly at the nodes. Spikelets
3.7-7 mm long, 1.9-2.4 mm wide, disarticulating at maturity, broadly ovate to
ovate. Lower glumes usually 1/4-2/5 as long as the spikelets, occasionally
1/2 as long or longer; upper glumes subequal to the spikelets; lower
florets sterile; lower lemmas similar in size to the spikelet, usually
awned, awns to 5 cm; lower paleas well-developed; upper lemmas
3.5-4.5 mm, similar in length and width to the upper glumes, broadly elliptic
to ovate, with an acute, greenish tip; anthers to 0.8 mm. Caryopses
1.9-3 mm, light brown or tan; embryos 70-85% as long as the caryopses.
2n = 54.
Echinochloa oryzoides is a common weed of rice fields throughout the
world, growing in the flooded portions of the fields. It was included in Echinochloa
oryzicola by Gould et al. (1972), but it differs in its shorter embryo,
lax, strongly drooping panicle, and earlier (June-July) flowering period. This
flowering period is also earlier than that of Oryza.
In addition, E. oryzoides is usually conspicuously awned, having longer
awns than even the awned variants of E. oryzicola, and it is rarely obviously
pubescent on the cauline nodes, leaf sheaths, and collars. The earliest known
collection of Echinochloa oryzoides in the United States was made in
1925 (Barrett and Seaman 1980).