Persicaria bicornis (Raf.) Nieuwland, pink smartweed. Annual (aquatic), taprooted, several–stemmed at base, not rosetted, with several ascending branches, ascending to suberect, in range to 150 cm tall; shoots with cauline leaves, appearing nearly glabrous, gland–dotted on lower surface of foliage.
Stems cylindric, swollen above each node, purple–red at node and on swelling, at midinternode with 1 flat face, glabrous.
Leaves helically alternate, simple, petiolate, with stipules; stipules (2) fused into cylinder and sheathing stem (ocrea) and attached to petiole mostly 6—9 mm long, membranous–brown, in range typically lacking cilia on margin, aging papery and brittle; petiole broadly channeled, to 10 mm long; blade lanceolate, in range < 65—105+ × < 13—22+ mm, tapered at base, short–ciliate on low teeth on margin, acuminate at tip, pinnately veined with midrib raised on both surfaces and lateral veins slightly raised on lower surface, in range upper surface without triangular or crescent–shaped blotch, lower surface conspicuously gland–dotted.
Inflorescences spikelike panicles, terminal, erect, heterostylous with all flowers on a plant with either short styles and short stamens (included) or lower styles and stamens (anthers and stigmas exserted), ± cylindric and uninterrupted, in range 38—55+ × 7—11 mm, often 2 per peduncle, each panicle of many, densely clustered, (2—)3—11–flowered cymes, cymes helically alternate, flowers arising sequentially in each cyme over numerous days, bracteate, glabrous; peduncle < 100 mm long below fork, with ascending branches to 80 mm long, bract at fork with ocrea and linear blade, ocrea truncate and membranous–brown, with short cilia on margin and often split, blade to 20 × 1.5 mm, 1–veined, branches swollen above fork and strawberry red to purple–red, axes often with 1 flat face and having stalked glandular hairs; bract subtending cyme (ocreola) closed, ca. 4 mm long, green with wide membranous margins below midpoint, short–ciliate from ends of veins; pedicel exserted 2—2.5 mm from ocreola, somewhat flattened with several glandular hairs on margins
Short–styled flower bisexual, ± radial, 4 mm across; buds light rose to pale pink (aging white); perianth 5–lobed, ca. 4 mm long; tube funnel–shaped, 1 mm long, green; lobes ascending (not revealing stamens), mostly obovate, ca. 3 × 1.7 mm; stamens (6—)8 in 2 whorls, fused to perianth tube at or slightly below sinuses; filaments to 1 mm long, white, of outer whorl having a pair of greenish nectary lobes associated with filament base; anthers dorsifixed, dithecal, 0.7 mm long, pink–rose, longitudinally dehiscent; pollen pale pink (whitish); pistil 1, ca. 1.6 mm long; ovary superior, discoid, 0.4 mm, glossy green, glabrous, 1–chambered with 1 ovule; style ca. 1.2 mm long, 2–branched from just below midpoint, pale green below fork, the branches 0.7 mm long, white, with terminal stigma
Long–styled flower bisexual, ± radial, 4 mm across; buds rose to pink; perianth 5–lobed, ca. 4 mm long; tube funnel–shaped, 1 mm long, green, somewhat beaded on outer surface; lobes ascending (revealing stamens and style), mostly obovate, ca. 3 × 1.7 mm, pink to rose above midpoint and often white at base (next to green tube); stamens 8 in 2 whorls, fused to perianth tube at or slightly below sinuses; filaments ± 3.5 mm long, white, of outer whorl having a pair of greenish nectary lobes associated with filament base; anthers dorsifixed, dithecal, 0.7 mm long, dark rose, longitudinally dehiscent; pollen pale pink; pistil 1, 3.6—4 mm long; ovary superior, discoid, 0.4 mm, glossy green or pale strawberry red, glabrous, 1–chambered with 1 ovule; style 3 mm long, white, 2–branched, the branches ca. 1.5 mm long, with terminal stigmas.
Fruit achene, round–discoid, ± 2.5 × 2.5 × 1 mm, glossy black and nearly smooth, 1 face with bump center at base; enclosed within dried perianth.
A. C. Gibson