Herb, annual, to 45 cm tall, glabrous; rhizome absent; stolon present. Leaves submersed or emerged; emerged leaves pale green to green-brown, petiole terete, 0.4-28.5 x ca. 0.05 cm, basal sheath to 2 cm long, blade linear-elliptic to narrowly elliptic, 1-7.4 x 0.2-1.8 cm, margin entire, apex acute, base acute to attenuate, basal lobes absent, veins 1-3, pellucid markings present as separate lines; submersed leaves pale green, petiole ridged, to 12 x 0.02-0.03 cm, blade linear-elliptic, 3.8-6.5 x 1-1.5 cm, margin entire, apex acute, base acute to attenuate, veins 3, pellucid markings present as separate lines. Inflorescence umbelliform or rarely racemose, erect, with 1-2 whorls, overtopping leaves, not vegetatively proliferating, 5-15 x to 10 cm; whorls with 6-15 flowers; peduncle with 4-5 ridges, not winged, 3.5-31.5 x ca. 0.1 cm; rachis, if present, terete between whorls, not winged; bracts shorter than pedicel subtended, united, connate half of length, delicate, deltoid, 2.8-3.5 x 1-2 mm, apex acute, not dilated basally; pedicels in flower and fruit spreading, 1.1-6.2 x ca. 0.05 cm. Flowers 0.8-1.7 cm wide; sepals in flower and fruit spreading, 2.8-3.6 x 2.8-3.6 mm, margin hyaline, with 7 veins, not papillose; petals clawed, 2.5-4.1 x 1.5-3 mm, claw ca. 1 mm long; stamens 9, filaments 1.8-2.1 mm long, anthers basifixed, 0.5-6 mm long, apex obtuse; carpels 15-20. Fruit terete, obovate, 0.8-1.8 x 0.8-1.3 mm, 3-4-ribbed, without keel, eglandular, beak lateral, erect, 0.1-0.3 mm long.
Argentina present, Caribbean Islands present, Guianas present, S Mexico present
from S Mexico and Caribbean Islands, S to Argentina; over 100 collections examined, including 7 from the Guianas (GU: 6; SU: 1).