Plants glabrous or sparsely pubescent in the distal younger parts of stems and branches. Stems erect or sometimes ascending proximally, much-branched and bushy, rarely nearly simple, 0.3-1(-2) m; each node with paired, divergent spines (modified bracts) to 1.5(-2.5) cm. Leaves: petiole ± equaling or longer than blade; blade rhombic-ovate, ovate, or ovate-lanceolate, 3-10(-15) × 1.5-6 cm, base broadly cuneate, margins entire, plane or slightly undulate, apex acute or subobtuse to indistinctly emarginate, mucronulate. Inflorescences simple or compound terminal staminate spikes and axillary subglobose mostly pistillate clusters, erect or with reflexed or nodding tips, usually green to silvery green. Bracts of pistillate flowers lanceolate to ovate-lanceolate, shorter than tepals, apex attenuate. Pistillate flowers: tepals 5, obovate-lanceolate or spatulate-lanceolate, equal or subequal, 1.2-2 mm, apex mucronate or short-aristate; styles erect or spreading; stigmas 3. Staminate flowers: often terminal or in proximal glomerules; tepals 5, equal or subequal, 1.7-2.5 mm; stamens 5. Utricles ovoid to subglobose, 1.5-2.5 mm, membranaceous proximally, wrinkled and spongy or inflated distally, irregularly dehiscent or indehiscent. Seeds black, lenticular or subglobose-lenticular, 0.7-1 mm diam., smooth, shiny. Flowering summer-fall. Waste places, fields, roadsides, railroads, barnyards, overgrazed pastures, other disturbed habitats; 0-700 m; introduced; Man., Ont.; Ala., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; West Indies; Central America; South America; introduced nearly worldwide. Amaranthus spinosus is native to lowlands in tropical America; at present it is a pantropical weed that also occurs in some warm-temperate regions.