Perennial, aquatic, tufted or stoloniferous. Culms decumbent, rooting and tillering at nodes, sometimes floating, lower part spongy, 0.7–1.5 m or more tall. Leaf sheaths slightly inflated below, upper sheaths tight, glabrous, auricles conspicuous, glabrous or ciliate; leaf blades up to 40 × 1–2 cm, margins and midrib scabrid, apex acuminate; ligule up to 17 mm. Panicle spreading, 12–30 cm, eventually nodding; branches 1–5 at lowest node, longest 2.5–12 cm, axils bearded or glabrous. Spikelets oblong, 8–11 mm, length 2.7–4.5 times width, yellowish green with reddish apex, deciduous; sterile lemmas lanceolate, ca. 2.5 mm, apex acuminate; fertile lemma finely reticulate with scattered short glassy hairs, flanks slightly sulcate, keel stiffly ciliate, apex acuminate; awn 5–40 mm or more, stout, scaberulous. Anthers 4–6 mm. Caryopsis reddish brown, 5–7 mm. Fl. and fr. Apr–May and Oct–Nov. 2n = 24.
"Annuals. Culms to 80 cm high, erect, tufted; nodes glabrous. Leaves 15-35 x 0.8-1.2 cm, linear-lanceolate, base rounded, apex acuminate; sheaths to 20 cm long, keeled; ligules 0.5-1.5 cm long, ovate, membranous. Panicles 12-25 cm long, lax. Glumes 2-3 mm long, ovate, unequal. Lemmas 8-10 mm long, ovate-oblong, laterally compressed, 3-nerved, awned; awns 5-10 mm long. Palea 6-10 mm long, oblong. Stamens 6: anthers 2-3 mm long , yellow. Stigmas cream-coloured. Grains 5-6 mm long, elliptic."
Isotype for Oryza sativa var. paraguayensis Parodi Catalog Number: US 1645646 Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany Preparation: Pressed specimen Collector(s): H. Weddell Year Collected: 1845 Locality: Paraguay, South America
Isotype: Parodi, L. R. 1933. Physis (Buenos Aires). 11: 244.