Leafless swallow-wort

Cynanchum scoparium Nuttall, Amer. J. Sci. Arts 5: 291. 1822; Amphistelma scoparium (Nuttall) Small; Metastelma scoparium (Nuttall) Vail

Stems woody at base, not corky. Leaves caducous, with 1 stipular colleter on each side of petiole; petiole 1–5 mm, adax­ially grooved, glabrous or sparsely puberulent; blade single-veined to faintly pinnate, linear, 10–50 × 1.5–4 mm, chartaceous, base cuneate, tapering to petiole and conduplicate, laminar colleters absent or hidden in groove, margins planar, apex acute, mucronulate, surfaces glabrous abaxially, minutely puberulent on midvein adaxially, margins remotely puberulent. Inflorescences 4–8-flowered. Pedicels 2.5–4 mm, pilosulous. Flowers: calyx lobes ovate, apices obtuse, 0.5–1 mm, pilosulous to usually glabrate, margins scarious; corolla tube 0.5 mm, lobes erect with spreading tips, linear, 2–2.5 mm, glabrous; corona segments basally connate and united to base of column, yellow to green, laminar, ovate, 0.5 mm, much shorter than gynostegium; gynostegium sessile; style apex planar. Follicles 4–7 × 0.2–0.4 cm, apically acuminate. Seeds 6–10, 5 mm; coma 2–2.5 cm.

Flowering nearly year-round; fruiting (Oct–)Jan–Feb(–Apr). Moist or dry hammocks, salt marshes, baygalls, swamp margins, canal banks, limestone, shell mounds, sandy soils; 0–50 m; Fla., Ga., S.C.; West Indies; South America.

Plants of Orthosia scoparia may appear densely leafy or completely leafless and may bear flowers in either condition. The flowers of O. scoparia are smaller than those of the regionally co-occurring spe­cies of Metastelma and Pattalias and, unlike those in Metastelma, the corollas of O. scoparia are completely glabrous. Orthosia scoparia just enters South Carolina (Beaufort County), where it is rare and considered to be of conservation concern.