Plants annual, glabrous. Stems prostrate or ascending (very rarely suberect), much-branched (usually from base), (0.1-)0.2-0.6(-1) m. Leaves: petiole ± ¹/2 as long as blade; blade obovate, elliptic, or spatulate, 1-2(-4) × 0.5-1(-1.5) cm, base cuneate and tapering, margins usually entire, plane, rarely slightly undulate, apex obtuse, rounded, mucronulate. Inflorescences axillary glomerules, green. Bracts of pistillate flowers narrow, thin, 1.5-5 mm, ± equaling or slightly exceeding tepals. Pistillate flowers: tepals (3-)4-5, narrowly ovate to broadly linear, unequal or subequal, 1.5-3 mm, thin, apex acute or acuminate; style branches spreading; stigmas 3. Staminate flowers intermixed with pistillate; tepals 3(-4); stamens 3. Utricles broadly ovoid, 1.7-2.5 mm, equaling tepals, mostly smooth (slightly verrucose or rugose in dry plants), dehiscence regularly circumscissile. Seeds black, lenticular to broadly plumply lenticular, 1.3-1.6 mm diam., rather dull. Flowering summer-fall. Disturbed habitats: roadsides, riverbanks, railroads, fields, waste places, sandy flats; 0-2200 m; Alta., B.C., Man., Ont., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; introduced and often completely naturalized in South America, Eurasia, and other regions. The name Amaranthus graecizans often has been misapplied to both A. blitoides and A. albus in older North American floras and manuals. Amaranthus blitoides was probably originally native to central and partly eastern United States, but now it is widely and successfully naturalized almost everywhere in temperate North America and in many subtropical to warm-temperate regions. It has not been reported from Mississippi or North Carolina but since it is found in all other conterminous United States it can be expected to occur in these two as well.

Varieties have been described within Amaranthus blitoides; most of them are of no taxonomic significance, being mostly ecologic forms or local morphologic variants. Among the infraspecific taxa, the most constant is var. reverchonii Uline & W. L. Bray, with narrower, more elongated leaves.

Plants annual, pubescent in distal parts or becoming glabrescent at maturity. Stems erect to ascending or decumbent, branched at or distal to base, 0.1-0.9 m. Leaves: petiole variable in length; blade lanceolate to nearly linear or rhombic-ovate to elliptic-ovate, (1.5-)2-4(-5) × 1-3 cm, base cuneate to broadly cuneate, margins entire, plane, rarely indistinctly undulate, apex subacute to obtuse or emarginate, mucronulate. Inflorescences axillary glomerules, green. Bracts lanceolate, subspinescent, 1.5-2 mm, shorter or slightly longer than tepals. Pistillate flowers: tepals 3, erect, elliptic to lanceolate-elliptic, equal or subequal, 1.5-2 mm, apex short-acuminate; style branches slightly spreading; stigmas (2-)3. Staminate flowers intermixed with pistillate; tepals 3, equal or subequal; stamens 3. Utricles subglobose to broadly elliptic, 2-2.5 mm, slightly rugose, dehiscence regularly circumscissile, rarely irregularly dehiscent. Seeds black, lenticular, 1-1.3(-1.6) mm diam., smooth or indistinctly punctate. Flowering summer-fall. On ballast; 0 m; introduced; N.J.; native to Eurasia (Mediterranean area, s Asia); n Africa; locally introduced in Australia. In North America the name Amaranthus graecizans has been constantly misapplied to the common North American taxa A. albus and A. blitoides. Consequently, A. graecizans has been excluded from lists of North American plants. Recently, herbarium specimens (casual aliens collected in 1879 on ballast in Camden, New Jersey) of A. graecizans subsp. sylvestris were discovered (M. Costea et al. 2001b). Probably, the species disappeared in North America long ago, but, considering the long history of misidentification and confusion, there is also some chance that it may occur locally as an introduced species. Three subspecies are usually recognized within Amaranthus graecizans in the Old World: subsp. graecizans, subsp. sylvestris (Villars) Brenan, and subsp. thellungianus (Nevski) Gusev. Only subsp. sylvestris, characterized by rhombic-ovate to elliptic-ovate leaves (as compared to lanceolate to almost linear leaves in subsp. graecizans) and comparatively large seeds has so far been reported from North America.

Despite its superficial similarity to Amaranthus albus and A. blitoides, A. graecizans seems to be more closely related to other Old World taxa with trimerous flowers.

Plant: Annual herb, prostrate, 3-7 dm, monoecious Leaves: cauline petiole 4-30 mm, blade 5-40 mm, elliptic to widely (ob)ovate, early-deciduous; axillary leaves smaller, persisten INFLORESCENCE: clusters axillary, throughout plant; bracts 1-3.5 mm, < or = sepals, midrib thick, spine-tipped, green, margins scarious especially near base Flowers: Staminate flower: sepals 4-5, 1.5-2.5 mm; stamens (3)4-5; Pistillate flower: sepals 4-5, 1-3.5 mm, oblong to ovate, outer 2 > others, more reflexed, tips more tapered and spiny Fruit: ± 2.5 mm, circumscissile; lid often rough below; Seed 1.3-1.7 mm wide, black; margin acute Misc: Waste places; < 2200 m.; Jul-Nov