Amaranthus blitoides S. Watson, prostrate pigweed, procumbent pigweed, prostrate amaranth. Annual, taprooted, not rosetted, several—many–stemmed at base with procumbent shoots radiating but not rooting, when decumbent to 15 cm tall; shoots to 70 cm long, never spinescent, with most leaves on axillary shoots, appearing glabrous.
Stems irregularly ridged, to 5 mm diameter, with 2 ridges descending from each leaf, green becoming tannish to reddish, often with whitish streaks ± straight on main axis, with short, colorless nonglandular hairs and sessile glandular hairs on younger growth, ± sandlike–papillate on older stems.
Leaves helically alternate, simple, petiolate, without stipules; petiole short—30 mm long, flared at base, whitish on margins; blade elliptic or obovate to oblong or ovate, 5—40 mm long, relatively small and folded upward on axillary shoots, bluish green, tapered at base, entire and white on margins, obtuse and with a short point to notched with a pointed extension of midrib at tip, pinnately veined with principal veins sunken on upper surface and whitish and raised veins on lower surface, glabrescent.
Inflorescence short, highly condensed cymes of unisexual flowers (cymules), axillary, spikelike throughout the plant, typically < 10 mm long, many–flowered, with sessile staminate flowers at base of cymule and more numerous pistillate flowers above on spikelike axes, bracteate, glabrous; bracts persistent along rachis, awl–shaped, 1—2(—3.5) mm long, short–pointed at tip but not spinescent, green with membranous margins; axes zigzagged when mature; bractlet (bracteole) subtending flower 1, resembling bract but smaller, ca. 60° alternate to bract, persistent on rachis.
Staminate flower radial, ca. 1 mm across; perianth parts (tepals) 3—5, equal, cupped–lanceolate, 1.5—2(—2.5) mm long, scarious–white with green midstripe, acuminate at tip; stamens 3—5, free, attached along margin of nectary; filaments 1.2—1.6 mm long, whitish; anthers dorsifixed, dithecal, linear, ± 1 mm long, pale yellow, longitudinally dehiscent; pollen yellow; nectary papillate; pistil absent.
Pistillate flower radial, ca. 1 mm across; perianth (tepals) 4—5, barely fused at base and persisting on fruit base, not spinescent, subequal (unequal when the innermost tepal is weakly developed), oblong or ovate, the longest sepal ca. 2 mm long and greenish, the shortest on the opposite side of pistil and narrower, ± colorless with faint green midstripe; stamens absent; pistil 1; ovary superior, compressed–ovoid, 1.5 mm long, green, 1–chambered with 1 ovule; styles 2—3, ascending; stigmas papillate.
Fruit compressed utricle, dehiscent around circumference (circumscissile) with top easily separated as cap when touched, 1–seeded, seed vertically oriented, surrounded by persistent calyx, readily abscising from plant, papery, light brown with persistent short–beaked styles, with thin, cobblestonelike wall.
Seed lens–shaped, 1.3—1.7 mm diameter, 1 mm thick, glossy black, smooth.
A. C. Gibson & B. A. Prigge