Amaranthus muricatus
Amaranthus spinosus
African amaranth, muricate amaranth
spiny amaranth, thorny amaranth
ascending or prostrate, much-branched from stout rootstock, 0.1–0.4 m.
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 to 1/2 as long as blade;
blade linear to narrowly lanceolate, 1.5–8 × 0.2–0.5(–1) mm, base tapering, margins entire, plane to undulate, apex obtuse and often emarginate.
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.
of pistillate flowers linear, 0.7–1.2 mm, 1/2–2/3 as long as tepals.
of pistillate flowers lanceolate to ovate-lanceolate, shorter than tepals, apex attenuate.
terminal, compact pyramidal panicles and axillary glomerules, erect or reflexed, green, leafless at least distally.
simple or compound terminal staminate spikes and axillary subglobose mostly pistillate clusters, erect or with reflexed or nodding tips, usually green to silvery green.
intermixed with pistillate or at tips of inflorescences;
tepals 5;
stamens 5.
often terminal or in proximal glomerules;
tepals 5, equal or subequal, 1.7–2.5 mm;
stamens 5.
tepals 5, narrowly oblanceolate, not clawed, equal, 1.5–2 mm, apex obtuse or subacute;
style branches erect;
stigmas 3.
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.
black, lenticular, 1–1.2 mm diam., semiglossy.
black, lenticular or subglobose-lenticular, 0.7–1 mm diam., smooth, shiny.
compressed, subglobose, 1.7–2 mm, ± equaling or slightly exceeding tepals, muricate, indehiscent.
ovoid to subglobose, 1.5–2.5 mm, membranaceous proximally, wrinkled and spongy or inflated distally, irregularly dehiscent or indehiscent.
Amaranthus muricatus
Amaranthus spinosus
The vernacular name “African amaranth” is sometimes used for this species; it is a misnomer; the species is native to South America and naturalized in Africa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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