Spindleroot, hairy or Rafinesque’s seedbox

Isnardia hirsuta (Desrousseaux) Roemer & Schultes var. permollis (Barton) de Candolle; I. hirtella (Rafinesque) Kuntze; Ludwigia permollis Barton

Roots fusiform, somewhat thick­ened, often fascicled. Stems subterete to angled, with raised lines or narrow wings decurrent from leaf axils, (30–)50–120 cm, well branched in distal 1/2, densely erect-hirsute to sometimes glabrous. Leaves: stipules narrowly deltate, 0.05–0.15 × 0.05–0.1 mm; sessile; blade closely appressed to stem, lanceolate to ovate-oblong, 1.4–5.5 × 0.4–1.2 cm, base attenuate, margins entire, apex acute to rounded, surfaces gla­brous or densely erect-hirsute; bracts usually very reduced, sublinear. Inflorescences leafy racemes, flowers solitary in leaf axils; bracteoles attached in subopposite pairs just proximal to ovary base, lanceolate-linear, 2.5–7 × 0.5–1.5 mm, margins entire, apex acute, surfaces hirtellous. Flowers: sepals narrowly ovate-deltate, (5.4–)6–12 × 2.2–4.5(–5) mm, margins entire, apex acute, surfaces hirtellous or, sometimes, glabrous; petals cordate, 12–14 × 13–14 mm, base attenuate, apex emarginate; filaments opaque white, awl-shaped, 2–5.5 mm, anthers 1.4–2.6 × 0.4–0.8 mm; ovary subcuboid or globose, 3–4 × 3–4 mm; nectary disc elevated, domed, 1–1.4 mm diam., prominently 4-lobed, ringed with stiff, spreading hairs or glabrous; style 1.3–4.5(–5.5) mm, glabrous, stigma capitate to hemispherical, 0.9–1.5 × 0.9–2(–2.5) mm, often shallowly 4-lobed, as long as stamens, sometimes exserted beyond them. Capsules subcuboid to squarish globose, 4–6 × 4–5 mm, 4-angled, often also 4-winged, wings 0.3–1.1 mm wide, pedicel 3–10 mm. Seeds light brown, oblong to reniform, 0.6–0.7 × 0.3–0.4 mm, surface cells elongate transversely to seed length. 2n = 16.

Flowering summer–early fall. Boggy depressions, roadside ditches, margins of boggy streams; 0–300 m; Ala., Ark., Del., D.C., Fla., Ga., Ky., La., Md., Miss., N.J., N.C., Okla., S.C., Tenn., Tex., Va.

A name often found in synonymy with Ludwigia hirtella is a later homonym: L. hirsuta Pursh 1813, not Desrousseaux 1789.