11. Amaranthus retroflexus L. (rough green amaranth, rough pigweed)
Pl. 197 g; Map
820
Plants
monoecious. Stems 30–200 cm long, erect or ascending, sparsely to densely
pubescent toward the tip with mostly crinkled, multicellular hairs, unarmed.
Leaves mostly long-petiolate. Leaf blades 2–12 cm long, lanceolate to ovate or
elliptic, narrowed or tapered to a usually bluntly pointed tip (often minutely
notched at the very tip), narrowed or tapered at the base, the surfaces
sparsely to moderately pubescent mostly along the veins with inconspicuous,
mostly crinkled, multicellular hairs, the upper surface sometimes glabrous or
nearly so. Inflorescences dull or grayish green occasionally dull
reddish-tinged; axillary and terminal; the axillary inflorescences short spikes
or less commonly dense, globose clusters; the terminal inflorescence usually a
panicle with numerous clusters of short, dense spikes (these branching along
most of the panicle axis); the flowers mostly continuous along the spikes; the
tip straight and usually stiffly erect; the main axis and branches moderately
to densely pubescent with mostly crinkled, multicellular hairs. Bracts 4–8 mm
long, the main body (excluding the awn) conspicuously longer than the sepals
and fruits, lanceolate to ovate, narrowed or tapered to a sharply pointed tip,
with a strongly thickened green midrib and relatively narrow, thin, papery
margins, the midrib extending beyond the main body as a short awn, spinelike at
maturity. Staminate flowers with (4)5 more or less similar sepals, these 2.0–2.6
mm long, slightly outward-curved, lanceolate to oblong-ovate, narrowed or
tapered to a sharply pointed tip, usually tapered to a short, awnlike extension
of the midrib at the tip. Stamens (4)5. Pistillate flowers with (4)5 more or
less similar sepals, these 2.2–3.0 mm long, outward-curved, narrowly oblong to
narrowly oblong-elliptic, truncate, rounded or shallowly notched at the soft
tip, sometimes with an abrupt, minute, sharp extension of the midrib. Stigmas
3, erect or ascending. Fruits 1.8–2.2 mm long, with circumscissile dehiscence,
the surface finely wrinkled above the midpoint when dry. Seeds 0.9–1.2 mm in
diameter, rounded along the rim, the surface reddish brown to more commonly
black. 2n=34. June–October.
Scattered,
mostly south of the Missouri River (native of most of North America and
portions of South America; introduced in Europe, Asia, Africa). Tops of bluffs
and upland prairies; crop fields, fallow fields, gardens, levees, pastures, farmyards,
feedlots, roadsides, railroads, and open, disturbed areas.