Plants annual, glabrous. Stems ascending to prostrate, erect when young, or main stems ± erect, branched proximally, 0.1-0.6 m. Leaves: petiole equaling or ¹/2 as long as blade; blade elliptic, oblanceolate to lanceolate, (0.5-)1-3(-3.5) × 0.3-2 cm, base tapering, margins entire, plane to slightly undulate, apex broadly rounded or emarginate. Inflorescences axillary clusters borne from base to top, axes thickened and inflated, becoming indurate at maturity (only in A. scleropoides and A. crassipes). Bracts of pistillate flowers keeled (only A. scleropoides and A. crassipes have keeled bracts), ovate-triangular, minute. Pistillate flowers: tepals 5, narrowly spatulate, slightly clawed, with expanded blade, equal or subequal, (1.2-)1.5-2.5 mm, apex acute to apiculate; claws indurate at maturity; style branches spreading; stigmas 2-3. Staminate flowers intermixed with pistillate; tepals 5, membranaceous; stamens 3. Utricles orbicular to compressed-obovoid, 1.1-1.5 mm, shorter than tepals, smooth to tuberculate in distal ¹/2, dehiscence regularly circumscissile. Seeds dark brownish black to black, compressed-ovoid to broadly lenticular, 0.9-1.1 mm diam., shiny. Flowering summer-fall. Seasonally wet, disturbed habitats; 0-1300 m; Okla., Tex.; Mexico (Tamaulipas). A hybrid between Amaranthus crassipes and A. scleropoides was recently described as A. ×texensis Henrickson and reported from southeastern Texas (J. Henrickson 1999).