10. Cuscuta polygonorum Engelm. (smartweed dodder)

Pl. 364 h; Map 1592

Stems relatively slender, usually less than 0.6 mm in diameter. Flowers 1.5–2.0 mm long, with smooth to slightly irregular surfaces, subtended by at most 1 lanceolate to ovate bract (usually none), in dense clusters on short side branches, the pedicels absent or very short. Calyces as long as or slightly longer than the corolla tube, 3- or 4-lobed 1/2–2/3 of the way to base, the lobes triangular to broadly ovate, rounded at the tip, not overlapping basally, not angled. Corollas narrowed or tapered to 3 or 4 sharply pointed lobes, these usually erect, with straight to slightly incurved tips. Infrastaminal scales usually not reaching filament bases, usually 2-lobed, toothed along the margins, usually slightly fringed near the tips. Fruits globose to depressed-globose, the wall not thickened at the tip. Seeds 1.3–1.5 mm long. July–September.

Scattered throughout the state (eastern U.S. and adjacent Canada west to Texas). Streams, ponds, swamps, bottomland forests, mesic upland forest slopes, and wet areas in prairies. Parasitic on a variety of mostly herbaceous hosts, including species of Amaranthus, Aster, Bromus, Cephalanthus, Justicia, Lycopus, Penthorum, Polygonum, Saururus, and Xanthium.