Globefruit primrose-willow

Isnardia sphaerocarpa (Elliott) de Candolle; Ludwigia sphaerocarpa var. deamii Fernald & Griscom; L. sphaerocarpa var. jungens Fernald & Griscom; L. sphaerocarpa var. macrocarpa Fernald & Griscom

Herbs often with prominent aerenchyma when base sub­merged, forming stolons 20–90 cm, 2–3.5 mm thick, floating, sometimes branched. Stems erect, slightly ridged, well branched, (40–)60–110 cm, densely strigillose or glabrous. Leaves alternate; stipules lanceolate-deltate, 0.1–0.4 × 0.1–0.2 mm; stolons: petiole ± winged, 0.1–0.3 cm, blade narrowly elliptic to oblanceolate or spatulate, 0.9–3 × 0.4–0.8(–1.3) cm, base attenuate, margins subentire with hydathodal glands, apex acute or obtuse; stems: petiole 0.1–0.4(–1) cm, blade narrowly elliptic or lanceolate to sublinear, on main stem (2.6–)6–10 × 0.5–1.1(–1.6) cm, on branches 2–5(–6) × 0.3–0.5(–0.6) cm, base attenuate or narrowly cuneate, margins entire with hydathodal glands mainly on primary cauline leaves, apex acute to very narrowly acute, surfaces glabrous or densely strigillose; bracts not much reduced. Inflorescences open, leafy racemes, more congested on branches, flowers solitary in leaf axils; bracteoles attached in subopposite pairs near base of ovary, usually linear to very narrowly lanceolate, rarely lanceolate, 0.5–1.5 × 0.1–0.3 mm, apex acuminate. Flowers: sepals ascending, yellow or cream adaxially, ovate-deltate, 2–3.5(–4) × 1.6–3(–3.3) mm, margins entire, apex acuminate, surfaces glabrous or densely strigillose; petals 0; filaments yellow, 1–1.7 mm, slightly dilated toward base, anthers 0.5–0.8 × 0.4–0.7 mm; pollen shed in tetrads; ovary broadly obovoid or cup-shaped, 1.5–3.5 × 2–3 mm; nectary disc elevated 0.4–0.6 mm on ovary apex, bright yellow, 1.5–3 mm diam., 4-lobed, glabrous or short-hirtellous between lobes; style yellow, 0.6–1(–1.3) mm, glabrous or strigillose proximally, stigma yellow, capitate to subglobose, 0.3–0.5 × 0.4–0.7 mm, not exserted beyond anthers. Capsules sometimes tinged pink, subglobose, subterete, 2–4(–4.5) × 2–4 mm, hard-walled, irregularly dehiscent, pedicel 0.5–1.2(–2.3) mm. Seeds brown to light brown, elliptic, 0.4–0.7 × 0.3–0.4 mm, surface cells transversely elongate to seed length, sometimes oblique. 2n = 32.

Flowering Jun–Sep. Drainage ditches, shores of slow-moving streams or ponds, marshes, swales, swamp forests, edges of limestone sinks, peaty bogs in pastures, interdunal marshes; 0–300 m; Ala., Conn., Del., Fla., Ga., Ill., Ind., La., Md., Mass., Mich., Miss., N.J., N.Y., N.C., Pa., R.I., S.C., Tenn., Tex., Va.

Ludwigia sphaerocarpa has its primary distribution along the Atlantic coastal plain, from Massachusetts to north-central Florida, and west along the Gulf coastal plain sporadically to southeastern Texas. Disjunct populations occur in south-central Tennessee, extreme southwestern Indiana, along Lake Michigan in northeastern Illinois and northwestern Indiana, and in west-central New York. In Michigan, L. sphaerocarpa is known from Allegan and Berrien counties, as reported by Reznicek and Voss in the Michigan Flora (https://michiganflora.net/species.aspx?id=1757).