Annual, monoecious, robust herb to 2 m; stems often red; indument of stems, young leaves and inflorescence-axes pubescent with tangled white hairs. Petiole to 13 cm long, shorter than to as long as blade; blade green to red or red-tinged, lanceolate, elliptical, ovate or rhomboid-ovate, (2.5-)6-20 x (1-)2-8 cm, apex obtuse or acute, often of much smaller size just below inflorescence, glabrous or somewhat puberulent below. Inflorescence of small axillary clusters and massive, lax, tail-like (thus, "caudatus") terminal panicles or spikesto 30(-50) cm long; bracts and bracteoles deltoid-ovate, lanceolate or lance-acuminate, 3.5 mm long, shorter than tepals, midvein excurrent, rigid arista at apex. Flowers green, white or reddish, at least some flowers with tepals recurved at apex at maturity. Male flowers interspersed throughout inflorescence; tepals 5, ovate to oblong, 2.5-3.2 mm long, acute; stamens 5. Female flowers more numerous; tepals 5, outer one tepal elliptical or oblanceolate, 1.5-2.8 mm long, acute, inner 4 tepals somewhat shorter than outer one, spathulate or oblong-spathulate, recurved; styles 3, erect. Utricles circumscissile, ovoid-globose, 2.0-2.5 mm, as long as or exceeding perianth, smooth or rugulose; seed subspherical or lenticular, 0.8-1.5 mm, variable in color, white, tawny, reddish-brown or black, dull or lustrous.
Andes Mts present, Guianas present present, South America present
Origin probably in the Andes Mts. of South America; cultivated as a grain or ornamental and locally escaped throughout the temperate and tropical zones; in the Guianas, the status is usually presumed as an escape from cultivation in former times and now naturalized as a weed; 11 collections examined, 5 from the Guianas (SU: 4; FG: 1).