Plants glabrous or nearly so. Stems erect, usually branched or occasionally ± simple, 0.4-1.5(-2) m; branches sometimes ascending. Leaves: petiole shorter than or rarely ± equaling blade; blade mostly narrowly ovate, obovate, elliptic, or lanceolate, 1.5-8 × 0.5-3 cm, thin and soft, base cuneate to nearly rounded, margins entire, plane or irregularly undulate, apex subacute to obtuse, with terminal mucro. Inflorescences mostly terminal, spikes to panicles, erect to nodding, rarely with axillary clusters in proximal part of plant. Bracts: of pistillate flowers with short, excurrent midrib, (1.5-)2-2.5 mm, equaling tepals or nearly so, apex acute or acuminate; of staminate flowers with prominent midribs, 2-3.5 mm, shorter than tepals, apex acute. Pistillate flowers: tepals spatulate, 1.5-2.5 mm, apex obtuse, with terminal mucro; style branches ± erect; stigmas 2-3. Staminate flowers: tepals 5, equal or subequal, 3 mm, apex obtuse to subacute; inner tepals with apex indistinctly mucronulate; stamens 5. Utricles light brown to brown, subglobose, 1.5-2 mm, shorter than tepals, walls thin, usually smooth. Seeds dark reddish brown, (0.9-)1-1.2 mm diam., shiny. Flowering summer-fall. Sandy habitats, sand hills, riverbanks, creeks, lakes, disturbed areas, agricultural fields; 0-2000 m; Ariz., Ark., Calif., Colo., Ill., Ind., Iowa, Kans., Ky., La., Mich., Mo., Mont., Nebr., Nev., N.J., N.Mex., Okla., Pa., S.Dak., Tenn., Tex., Va., Wis., Wyo. Amaranthus arenicola is native to the central and southwestern Great Plains, from Texas to Nebraska or South Dakota, and occurs as occasionally introduced in other regions of North America and in Europe, but it is not naturalized. However, many staminate specimens of A. tuberculatus have been misidentified as this species, and some of the state references listed above may be in error.