Slim Amaranth

Originally a riverside pioneer in eastern North America, now Amaranthus hybridus is extremely abundant in agricultural fields and other disturbed habitats. Related cultivated species have been reported from the flora area, including A. caudatus, A. hypochondriacus, and A. cruentus; there is no evidence that they are established; specimens identified as these species are often variants of A. hybridus.

Distribution of Amaranthus hybridus in North America needs clarification because the name was misapplied to other species, notably A. powellii, and specimens of A. retroflexus, A. powellii, and A. hybridus are frequently interchangeably misidentified. Forms of A. hybridus and A. powellii with reddish inflorescences are often misidentified as escaped and hence presumably naturalized, cultivated species A. caudatus Linnaeus, A. hypochondriacus Linnaeus, and A. cruentus Linnaeus.

Amaranthus hybridus is extremely variable. In particular, there are numerous North American specimens with subobtuse tepals and thick inflorescences, suggesting hybridization with A. retroflexus. In Europe such presumably hybrid forms are known as A. ×ozanonii Thellung (A. Thellung 1914-1919).

A new, presumably hybridogenous taxon, Amaranthus ×tucsonensis Henrickson, was recently described from Arizona (J. Henrickson 1999). It was suggested that one of its parents is A. hybridus; the other parental species (probably a species with obtuse or spatulate tepals) remains unknown. The problem of proper taxonomic position and origin of A. ×tucsonensis needs further study.

Annual herb, erect or less commonly ascending, up to c. 2 (-3) m in height, not infrequently reddish-tinted throughout. Stems stout, branched, angular, glabrous or thinly to moderately furnished with short or long multicellular hairs (increasingly so above, especially in the inflorescence). Leaves glabrous, or thinly pilose on the lower margins and underside of the primary nervation, long-petiolate (petioles up to 15 cm but even then scarcely exceeding the lamina), lamina broadly lanceolate to rhomboid or ovate, 3-19 (-30) x 1.5-8 (-12) cm, gradually narrowed to the blunt to subacute mucronulate tip, attenuate or shortly cuneate into the petiole below. Flowers in yellowish, green, reddish or purple axillary and terminal spikes formed of cymose clusters, which are increasingly closely approximate upwards, the terminal inflorescence varying from a single spike to a broad, much-branched, panicle up to c. 45 x 25 cm: in length and breadth, the ultimate spike not infrequently nodding; male and female flowers intermixed throughout the spikes. Bracts and bracteoles deltoid-ovate to deltoid-lanceolate, pale-membranous, acuminate and with a long, pale to reddish-tipped, erect arista formed by the stout, excurrent, yellow or greenish midrib, subequalling to much exceeding the perianth. Perianth segments (3-)5, 1.5-3.5 mm, lanceolate or oblong, acute-aristate or the inner sometimes blunt in the female flowers, only the midrib at most greenish. Stigmas (2-) 3, erect, flexuose or recurved, c. 0.75-1.25 mm. Capsule subglobose to ovoid or ovoid-urceolate, 2-3 mm, circumscissile, with a moderately distinct to obsolete “neck”, lid smooth, longitudinally sulcate, or sometimes rugulose below the neck. Seed black and shining or pale, compres¬sed, 0.75-1.25 mm, almost smooth centrally, faintly reticulate around the margins.

Plants glabrous or glabrescent, or distal parts of stem and branches slightly pubescent when young. Stems erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3-2(-2.5) m. Leaves: petiole ¹/2 as long as to equaling blade; blade ovate, rhombic-ovate, or lanceolate, (2-)4-15 × (1-)2-6 cm, base cuneate to broadly cuneate, margins entire, apex acute to obtuse, with mucro. Inflorescences terminal and axillary, erect or reflexed, occasionally nodding, green or olive green, occasionally with silvery or reddish purple tint, leafless at least distally, terrminal inflorescence often slightly nodding with numerous shorter branches at base. Bracts lanceolate-linear to subulate, 2-3.5(-4) mm, subequal to or 2 times as long as tepals }, apex spinescent. Pistillate flowers: tepals 5, lanceolate to lanceolate-linear, subequal or unequal, 1.5-3 mm, membranaceous, apex acute or acuminate, gradually narrowing into aristate tip; style branches erect, shorter than body of fruit; stigmas 3. Staminate flowers at tips of inflorescences; tepals 5; stamens (4-)5. Utricles obovoid or elongate-ovoid, 1.5-2.5 mm, shorter than tepals, smooth proximally, lid verrucose or rugose, dehiscence regularly circumscissile, or rarely in some presumably hybrid forms, irregularly dehiscent or indehiscent. Seeds black to dark reddish brown, lenticular to lenticular-globose, 1-1.3 mm, smooth, shiny.

Stem 30-50 cm tall, branched, pubescent. Petiole 1-2.5 cm, hairy; leaf blade ovate or ovate-rhombic, 3-4.5 × 1.5-2.5 cm, abaxially pilose, adaxially nearly glabrous, base cuneate, margin undulate, apex acute or notched, with a mucro. Complex thyrsoid structures terminal, slender, somewhat drooping at apex and in spikes. Bracts and bracteoles subulate, lanceolate, 3.5-4 mm, distinctly long pointed, longer than perianth. Tepals oblong-lanceolate, ca. 2 mm, apex acute, with a mucro. Stamens nearly as long as or slightly longer than perianth; stigmas 3. Utricles ovoid, longer than perianth, ca. 2 mm, circumscissile. Seeds black, subglobose, ca. 1 mm in diam. Fl. Jul-Aug, fr. Sep-Oct. 2n = 24, 32*, 33, 34.

B.C., Man., N.S., Ont., Que.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., Wash., W.Va., Wis.; Mexico; West Indies; Central America; South America; widely introduced or naturalized in tropical, subtropical, and warm-temperate regions worldwide.

Flowering summer-fall.

Waste places, agricultural and fallow fields, railroads, roadsides, riverbanks, other disturbed habitats; 0-2500m.

Farms, waste places, hillsides. Anhui, Fujian, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Sichuan, Zhejiang [Bhutan, Japan, Laos, Nepal, Sikkim, Vietnam; Europe, North and South America].