Thorny Pigweed

Nile Valley north of Nubia (Cairo).

American origin.

Weeds of cultivation, naturalized.

Annual.

Amaranthus spinosus is native to lowlands in tropical America; at present it is a pantropical weed that also occurs in some warm-temperate regions.

Amaranthus spinosus, or its ancestral taxon, probably gave rise to the allopolyploid A. dubius by hybridization with some species of the A. hybridus aggregate (see above). Section Centrusa probably occupies a basal position, at least for the clade of subg. Amaranthus sect. Amaranthus, and probably for some representatives of subg. Acnida as currently outlined. Recent results of sequencing the ITS region (including ITS-1, 5.8S rDNA, and ITS-2) of nuclear ribosomal DNA from 15 species of Amaranthus occurring in China also suggest the basal position of A. spinosus among the studied species (Song B. H. et al. 2000). These results also confirm a profound divergence between subgenera Amaranthus and Albersia; the latter is called "sect. Paucestamen" by the above authors. Data on the electrophoretic variation of seed proteins (R. H. Sammour et al. 1993) are also in accord with the segregation of these two subgenera; in the cited article, these groups are called sect. Amaranthus and sect. Blitopsis.

Amaranthus dubius Mart. ex Thell. may yet be found in, or be introduced into, Pakistan. It much resembles Amaranthus spinosus but lacks the axillary spines and has a different habit; from robust Amaranthus viridis it differs in its circum¬scissile capsule, which is much less strongly wrinkled than that of Amaranthus viridis.

Annual herb, erect or slightly decumbent, simple or much-branched and bushy, up to 1.5 m in height. Stem stout, sometimes reddish, usually branched, angular, glabrous or increasingly furnished above (especially in the inflore¬scence) with long, multicellular, flocculent hairs. Leaves glabrous, or thinly pilose on the lower surface of the primary nervation, long-petiolate (petioles up to c. 9 cm, sometimes longer than the lamina), the lamina ovate to rhomboid-ovate, elliptic, lanceolate-oblong or lanceolate, c. 1.5-12 x 0.8-6 cm, subacute or more commonly blunt or retuse at the tip with a distinct, fine, colourless mucro, cuneate or attenuate at the base; each leaf-axil bearing a pair of fine and slender to stout and compressed spines up to c. 2.5 cm long. Flowers green, in the lower part of the plant in axillary clusters 6-15 mm in diameter; towards the ends of the stem and branches the clusters are leafless and approximated to form simple or sometimes (especially the terminal) branched spikes usually up to c. 15 cm long and 1 cm wide. Lower clusters entirely female, as are the lower flowers of the spikes; upper flowers of the spikes male, mostly for the apical 1/4-2/3 of each spike. Bracts and bracteoles deltoid-ovate, pale-membranous, with an erect, pale or reddish awn formed by the excurrent green midrib; bracteoles shorter than, subequalling or little exceeding the perianth, commonly smaller than the bracts. Perianth segments 5, those of the female flowers c. 1.5-2.5 mm, narrowly oblong or spathulate-oblong, obtuse or acute, mucronulate, frequently with a greenish dorsal vitta; those of the male flowers broadly lanceolate or lanceolate-oblong, acute or acuminate, only the midrib green. Stigmas (2-) 3, flexuose or reflexed, 1-1.5 mm. Capsule ovoid-urceolate with a short inflated neck below the style base, c. 1.5 mm, regularly or irregularly circumscissile or rarely indehiscent, the lid rugulose below the neck. Seed 0.75-1 mm, compressed, black, shining, very faintly reticulate.

Plants glabrous or sparsely pubescent in the distal younger parts of stems and branches. Stems erect or sometimes ascending proximally, much-branched and bushy, rarely nearly simple, 0.3-1(-2) m; each node with paired, divergent spines (modified bracts) to 1.5(-2.5) cm. Leaves: petiole ± equaling or longer than blade; blade rhombic-ovate, ovate, or ovate-lanceolate, 3-10(-15) × 1.5-6 cm, base broadly cuneate, margins entire, plane or slightly undulate, apex acute or subobtuse to indistinctly emarginate, mucronulate. Inflorescences simple or compound terminal staminate spikes and axillary subglobose mostly pistillate clusters, erect or with reflexed or nodding tips, usually green to silvery green. Bracts of pistillate flowers lanceolate to ovate-lanceolate, shorter than tepals, apex attenuate. Pistillate flowers: tepals 5, obovate-lanceolate or spatulate-lanceolate, equal or subequal, 1.2-2 mm, apex mucronate or short-aristate; styles erect or spreading; stigmas 3. Staminate flowers: often terminal or in proximal glomerules; tepals 5, equal or subequal, 1.7-2.5 mm; stamens 5. Utricles ovoid to subglobose, 1.5-2.5 mm, membranaceous proximally, wrinkled and spongy or inflated distally, irregularly dehiscent or indehiscent. Seeds black, lenticular or subglobose-lenticular, 0.7-1 mm diam., smooth, shiny.

Stem erect, green or somewhat tinged purple, 30-100 cm tall, terete or obtusely angulate, much branched, glabrous or slightly pubescent. Petiole 1-8 cm, glabrous, 2-armed at base; leaf blade ovate-rhombic or ovate-lanceolate, 3-12 × 1-6 cm, glabrous or slightly pubescent along veins when young, base cuneate, margin entire, apex obtuse, with a mucro. Complex thyrsoid structures terminal or axillary, 8-25 cm; terminal spike usually with all male flowers at or toward apex. Bracts becoming very sharply spiny in proximal part of spike. Tepals green, transparent at margin and with green or purple median band, apex acute, with a mucro; male flowers oblong, 2-2.5 mm; female flowers oblong-spatulate, ca. 1.5 mm. Filaments nearly as long as or slightly shorter than perianth. Stigmas 3(or 2). Utricles included in perianth, oblong, 1-1.2 mm, circumscissile slightly below middle. Seeds brownish black, subglobose, ca. 1 mm in diam. Fl. and fr. Jul-Nov. 2n = 34, 68.

Distribution: Of presumed American origin, now a cosmopolitan weed in the warmer regions of the world and also occurring as a casual in some temperate regions; in Pakistan as elsewhere it occurs as a weed of cultivation, roadsides, waste places etc., ascending to at least 1210 m.

Cosmopolitan warm temperate and tropical weed.

introduced; Man., Ont.; Ala., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; West Indies; Central America; South America; introduced nearly worldwide.

150-1200 m

Flowering summer-fall.

Waste places, fields, roadsides, railroads, barnyards, overgrazed pastures, other disturbed habitats; 0-700m.

Waste places, gardens. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shanxi, Sichuan, Taiwan, Yunnan, Zhejiang [probably native to neotropics, now cosmopolitan in warm-temperate and tropical regions].

spinosus: spiny

Annual herb, mostly erect, up to 1.5 m. Leaves glabrous or with sparse hairs on the main veins below, long petiolate, up to 9 cm. The leaf axils bear pairs of fine and slender spines. Flowers green in axillary clusters and branched terminal spikes. Male flowers in the apical part of the spikes.

Frequent

Throughout tropical and subtropical regions of the world; also sporadic in warm temperate areas

Amaranthus spinosus L. Sp. PI. 991. 1753
Amaranthus diacanthus Raf. Fl. Eudov. 31. 1817.
Amaranthus caracasanus H. B. K. Nov. Gen. & Sp. 2: 195. 1817.
Amaranthus spinosus rubricaulis Hassk. Flora 25: 14 tt. 20. 1842.
Amaranthus spinosus viridicaulis Hassk. Flora 25: I,itt. 20. 1842.
Amaranthus spinosus purpurascens Moq. in DC. Prodr. 13 2 : 260. 1849.
Amaranthus spinosus inermis Schum. & L-aut. Fl. Deuts. Schutzg. Siidsee 305. 1900.
Amaranthus spinosus circumscissus Thellung, in Asch. & Graebn. Syn. Mittel-Eur. Fl. 5: 269.
1914. Amaranthus spinosus basiscissus Thellung, in Asch. & Graebn. Syn. Mittel-Eur. Fl. 5: 269. 1914. Amaranthus spinosus indehiscens Thellung, in Asch. & Graebn. Syn. Mittel-Eur. Fl. 5: 269. 1914. Galliaria spinosa Nieuwl. Am. Midi. Nat. 3: 278. 1914. •
Stems stout and succulent, erect or ascending, 3-12 dm. high, glabrous below, more or less pubescent above, often reddish, striate or sulcate; petioles slender, 0.5-9 cm. long, often pubescent, bearing in the axils 2 rigid sharp-pointed spines 2-25 mm. long; leaf -blades ovate to rhombic-ovate or lanceolate, 1.5-12 cm. long, acute at the base, narrowed toward the apex but obtuse to broadly rounded at the tip, dark-green, glabrous or sparingly pubescent; flowers monoecious, the pistillate in dense, globose, sessile, mostly axillary clusters, the staminate in slender, erect or drooping, terminal spikes 3-18 cm. long and 4^8 mm. thick; bracts lanceolate to subulate, often spine-like, shorter than the sepals or sometimes 2-3 times as long; sepals of the pistillate flowers 5, oblong, obtuse or acute, 1.5 mm. long, those of the staminate flowers lance-oblong, acute or abruptly acuminate; stamens 5; style-branches 3; utricle ovoid, about equaling the sepals, irregularly and imperfectly circumscissile ; seed smooth, black, lustrous, 0.7-1 mm. in diameter. Type locality: India.
Distribution: Southeastern Canada and Maine to Minnesota, Florida, the West Indies, Mexico, and Panama; also in tropical and sub-tropical South America, Asia, and Africa; naturalized m central and southern Europe.
*^ lL ™S l* A T IONS , : ^ ld ^. Hist Amaranth, pi. 4, f. 8; Britt. & Brown, 111. Fl. /. 1400; ed. 2, /. 1662; Wight Ic. pi. 513; Fiori & Paol. Ic. Fl. Ital. /. 1044; Reichenb. Ic. Fl. Germ. 24: pi. 297, f. 3-5; Darl. Am. Weeds /_ 17 Ri Bull Mirh F™ stn im-ft?