Linnaeus, Sp. Pl. 2: 991. 1753.
Spiny amaranth, thorny amaranth
glabrous or sparsely pubescent in the distal younger parts of stems and branches.
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.
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.
simple or compound terminal staminate spikes and axillary subglobose mostly pistillate clusters, erect or with reflexed or nodding tips, usually green to silvery green.
of pistillate flowers lanceolate to ovate-lanceolate, shorter than tepals, apex attenuate.
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.
often terminal or in proximal glomerules; tepals 5, equal or subequal, 1.7-2.5 mm; stamens 5.
ovoid to subglobose, 1.5-2.5 mm, membranaceous proximally, wrinkled and spongy or inflated distally, irregularly dehiscent or indehiscent.
black, lenticular or subglobose-lenticular, 0.7-1 mm diam., smooth, shiny.
Flowering summer-fall. Waste places, fields, roadsides, railroads, barnyards, overgrazed pastures, other disturbed habitats; 0-700 m; 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.
is native to lowlands in tropical America; at present it is a pantropical weed that also occurs in some warm-temperate regions.
or its ancestral taxon, probably gave rise to the allopolyploid
by hybridization with some species of the
aggregate (see above). Section
probably occupies a basal position, at least for the clade of subg.
and probably for some representatives of subg.
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
occurring in China also suggest the basal position of
among the studied species (Song B. H. et al. 2000). These results also confirm a profound divergence between subgenera
; the latter is called "sect.
" 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.