Amaranthus scleropoides Uline & W. L. Bray, bonebract pigweed, bonebract amaranth. Annual, taprooted, not rosetted, several–stemmed at base, prostrate to low–decumbent, typically < 10 cm tall; monoecious; shoots never spinescent, with only cauline leaves, essentially glabrous.
Stems ± ridged, to 3 mm diameter, with 2 ridges descending from leaf, appearing tannish but actually pale green with whitish streaks ± straight on main axis (crystals within cells), somewhat fleshy, with persistent leaf bases.
Leaves helically alternate, simple, petiolate, without stipules; petiole channeled, 2—25(—40) mm long, pale green with whitish streaks and speckles, with some short hairs and domed cells; blade elliptic to obovate, < 4—35 × < 3—12 mm, tapered to long–tapered at base, entire to subentire and wavy on whitish margins and often with domed cells, rounded or truncate to slightly notched with short point (extension of midrib) at tip, pinnately veined with principal veins sunken on upper surface and raised on lower surface, lower surface somewhat glistening when fresh.
Inflorescence short, highly condensed cyme of unisexual flowers (cymules), axillary, typically < 7 mm long, several–flowered, commonly with 1 staminate flower with early anthesis in center at base of cymule and several pistillate flowers surrounding and above on spikelike axes, bracteate, glabrous; peduncle of cyme stout, ca. 1 × 1 mm and aging hard (indurate); bracts along rachis deltate, 0.5—0.9 mm, green–keeled with membranous margins aging scarious, short–ciliate on margins, with bases aging swollen and ridged and becoming indurate; bractlet (bracteole) subtending flower 1, resembling bract but smaller, ca. 60° alternate to bract, persistent on rachis.
Staminate flower radial, ca. 1 mm across; tepals (perianth parts) 5, unequal, broadly lanceolate to narrowly obovate and keeled with whitish point at tip (extension of keel), 1—1.5 mm long, membranous aging scarious with green keel; stamens 3, free, exserted; filaments 1.2—1.4 mm long, whitish; anthers dorsifixed, dithecal, linear, ± 0.8 mm long, light yellow, longitudinally dehiscent; pollen yellow; pistil absent.
Pistillate flower radial, < 1 mm across; perianth (tepals) 5, barely fused at base and persistent on fruit base, not spinescent, conspicuously unequal, obovate to spatulate, 0.8—1.2 × 0.25—0.4 mm within each flower, the outermost the largest and often folded upward from midvein, the shortest, innermost tepal appearing clawed, membranous with green keel aging scarious, in fruit mostly rounded and usually without point at tip (the outermost ± acute at anthesis), often sparsely short–ciliate; stamens absent; pistil 1; ovary superior, compressed–ovoid, ca. 0.7 mm long, green, 1–chambered with 1 ovule; styles 2(—3 occasionally and styles unequal), arching ascending; stigmas papillate.
Fruit compressed utricle, dehiscent around circumference (circumscissile) with top easily separated as cap when touched, 1–seeded, surrounded by persistent, scarious perianth, persistent on plant, papery, light brown with 2 persistent, suberect styles, cap 1—1.1 mm long, the lower portion ca. 0.5 mm long.
Seed lens–shaped (lenticular), 0.9—1.1 mm diameter, glossy dark brown–black to black (reddish when immature), smooth.
A. C. Gibson