Plants glabrescent to sparsely pubescent. Stems erect or ascending proximally, much-branched especially near base, 0.1–0.7 m. Leaves: petiole less than 1/2 as long as blade; blade oblanceolate or lanceolate to ovate-lanceolate, (1.2–)1.5–5(–7) × 0.3–2 cm, base narrowly cuneate to cuneate, margins entire, plane or slightly undulate, apex acute to subobtuse, mucronulate. Inflorescences axillary clusters, toward apex aggregated in spikes (rarely spicate panicles), axes, leafy (occasionally almost leafless distally). Bracts lanceolate to linear-subulate, 1.3–3.5 mm, slightly longer than tepals. Pistillate flowers: tepals 5, spatulate to narrowly spatulate, clawed, equal or subequal, 1.5–2.5 mm, margins entire, apex obtuse, rounded, or slightly emarginate; style branches erect; stigmas 3. Staminate flowers: mostly at tips of inflorescences; tepals 5, equal or subequal; stamens 3(–5). Utricles obovoid to subglobose-obovoid, 1.5–2 mm, nearly equaling or slightly shorter than tepals, smooth, dehiscence regularly circumscissile. Seeds black, subglobose to broadly lenticular, 1 mm diam., smooth, shiny.
Phenology: Flowering summer–fall.
Habitat: Sandy, rocky, and gravelly flats, slopes, canyons, washes, other naturally disturbed habitats
Elevation: 1000-1700 m
Ariz., Calif., N.Mex., Tex., Mexico.
The name Amaranthus torreyi has been widely misapplied to at least two other species, 7. A. arenicola and 6. A. watsonii. Because of that, the name A. bigelovii was used for A. torreyi by J. D. Sauer (1955) and in some recent floras. Sometimes A. torreyi (California and Arizona) and A. bigelovii (New Mexico and Texas) are recognized as separate species. The nomenclature and taxonomic relationships in this group should be critically reviewed based on type specimens and additional experimental and field studies.