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.

Flowering summer-fall. Sandy, rocky, and gravelly flats, slopes, canyons, washes, other naturally disturbed habitats; 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.

FNA 2004, Kearney and Peebles 1969

Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Herbaceous annuals to 1 m tall, stems erect to ascending, much branched, especially near the base; herbage glabrous to sparsely pubescent. Leaves: Alternate and petiolate, the petioles less than half as long as the blades; blades oblanceolate to lanceolate, to 5 cm long and 2 cm wide, with entire margins and pinnate veination; stipules absent. Flowers: Small and green, in axillary clusters equal to or longer than petioles, and graduating to dense leafy spikes at branch tips; plants monoecious (male and female flowers on the same plant). Bracts subtending flower clusters are lanceolate to narrowly awl-shaped, hyaline, scarious, and equal to or longer than the flowers. Pistillate flowers have 5 distinct, clawed tepals, these with entire margins; staminate flowers borne mostly at inflorescence tips, with 5 equal to subequal tepals, inflorescence bracts. Bracts and perianth segments not becoming rigid and spinose. Fruits: Utricles 2 mm, circumsessile (dehiscing so the top opens like a lid), subglobose, shorter than the calyx, 2-3 beaked by the persistent styles. Seeds black, smooth, shiny. Ecology: Found on sandy, rocky, and gravelly flats, slopes, canyons, washes, and other naturally disturbed habitats; 3,500-5,500 ft (1067-1676 m); flowering summer-fall. Distribution: Arizona, California, New Mexico, Texas; Mexico. Notes: Amaranthus species are notoriously difficult and commonly misidentified. Pay close attention to the following characters and take samples if unsure. A. torreyi distinguished by having generally shorter inflorescence spikes at the branch tips than most spiked Amaranthus in the region; possesses mostly axillary inflorescences with some aggregating into leafy spikes, the inflorescences all equal to or longer than leaf petioles; seed-bearing (pistillate) flowers with 4, spatulate tepals with smooth (entire) margins; and lanceolate leaves. A. fimbriatus also has narrow leaves and flowers in axillary glomerules and terminal leafy spikes. However, A. fimbriatus has longer, narrower leaves, only 1-5 mm wide, with long-tapering bases, and pistillate tepals with fringed or toothed margins. Ethnobotany: There is no specific use given for the species, but the genus was used as a food source; the seeds were ground into meal and the leaves were boiled and eaten as greens. Synonyms: None Editor: LCrumbacher 2011, FSCoburn 2014 Etymology: Amaranthus comes from the Greek amarantos, "unfading," referring to the long-lasting flowers, while torreyi is named after John Torrey (1796-1873), a professor of chemistry and one of the giants of North American botany who described hundreds of plants from the Mexican Boundary and the Pacific railroad survey expeditions.