Distribution: Wet places such as pond margins and depressions, wet sand ditches and prairies; classified as tenagophyte (amphibious plants of wet or regularly flooded areas) by Cook (1968). From central and southern Florida in the United States, the West Indies and central and southern Mexico, through all Central America; in South America it is common in the Guianas, Venezuela, Colombia, Ecuador, and Peru, very scattered in Brazil, and known only from one collection each in Paraguay and in Bolivia. Introduced in the Old World throughout tropical Africa (see Raven, 1963: 348). Collected in 1968 on refuse dumps in the Botanic Garden, Calcutta, India.
Habit: Erect glabrous annual herbs up to 3 m tall. Stem reddish, unbranched or profusely branching; branches erect, often ascending, angled from decurrent leaf bases, often winged along the angles, occasionally becoming woody and terete below.
Leaves: Leaves 2-20 cm long, 0.2-4 cm wide, elliptic or sometimes narrowly lanceolate, with 10-15 veins on each side of midrib, secondary veins anastomosing, submarginal vein prominent, membranous, glabrous or sometimes minutely strigillose along veins below, minutely scabrid along margin, acute or acuminate at tip, acute at base, continuing as decurrent leaf bases, bracts often reduced, flowers subsessile, bracteoles 0.3-0.4 mm long, ca. 0.2 mm wide, scale-like, turning black, with no glands subtending them, borne at base of or on the lower half of the ovary, stipules ca. 0.2 mm long and wide, deltoid, petioles 2-22 mm long, glabrous or sometimes minutely strigillose.
Flowers: Sepals 4, 3-6 mm long, 1-17 mm wide, ovate or lanceolate, acute or short-acuminate at apex, glabrous or sometimes strigillose, petals 35-5 mm long, 2-25 mm wide, obovate, yellow, stamens subequal, staminal filaments 1.3-1.5 mm long, anthers 0.6-1 mm long, ca. 0.4 mm thick, oblong, ovary 4-10 mm long, 2-4 mm thick, 4-angled, obconic, glabrous or rarely strigillose, disk plane, subglabrous, style 0.5-1 mm long, 0.5-0.6 mm thick, stigma 1-1.2 mm thick, globose.
Fruit: Capsule irregularly dehiscent 10-22 mm long, 2-4 mm in diameter, thin-walled, glabrous or occasionally strigillose, 4-angled, subsessile.
Seeds: Seeds numerous, in many series or rows, free, 0.3-0.5 mm long, 0.2-0.3 mm wide, elongate-ovoid, raphe very reduced and inconspicuous.
Chromosomes: Gametic chromosome number: n = 8.
Notes: FNA, Self-pollinating.