Sp. Pl. 1: 17; 2: 1200. 1753.
Annuals. Stems ascending to erect, simple or few-branched, 4–50 cm, glabrous or glabrate proximally, glabrous or glandular-puberulent distally. Leaves: blade lanceolate to elliptic or oblong-obovate, 15–70 × 5–25 mm, margins entire or with 1–4 pairs of blunt or sharp teeth distally, apex obtuse to acute, surfaces glabrous. Pedicels stout, 1–12 mm, length 0.1–0.3 times bract, glabrous or sparsely glandular-puberulent; bracteoles 2, 2–6 mm. Flowers: sepals distinct, linear-lanceolate to lanceolate or oblong, 4–7 mm; corolla 8–15 mm, tube greenish white to greenish yellow or yellow, veins purple or brownish purple, limb white, sometimes tinged lavender; style 2–4 mm. Capsules subglobular, (3–)4–9 × 4–8 mm. Seeds 0.7–0.8 mm. 2n = 16.
Phenology: Flowering Mar–Oct.
Habitat: Stream banks, swamps, floodplain pools and ponds, swamps.
Elevation: 0–500 m.
Ala., Ark., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mich., Miss., Mo., N.J., N.C., Ohio, Okla., R.I., S.C., Tenn., Tex., Va., W.Va., introduced in Mexico (Veracruz).
Some plants from tidal wetlands in Maryland, New Jersey, and Virginia are purportedly relatively shorter in stature and bear shorter pedicels and smaller capsules than most plants of Gratiola virginiana. They have been treated as var. aestuariorum; the distinctness of var. aestuariorum has not been assessed in the context of morphological variation across the range of G. virginiana.