Med. Repos., hexade 3, 2: 333. 1811.
Perennials. Stems decumbent to ascending or erect, simple or few-branched, 5–47 cm, glabrous proximally, sparsely glandular-puberulent distally. Leaves: blade lanceolate-ovate to oblong or ovate-elliptic, sometimes linear-lanceolate on submerged plants, 5–26 × (1.5–)3–7(–9) mm, margins entire or with 1 or 2 pairs of teeth, apex obtuse, rarely acute, surfaces glabrous. Pedicels slender, (3–)5–20 mm, length 0.4–2.1 times bract, sparsely glandular-puberulent; bracteoles 2, 2–4 mm. Flowers: sepals distinct, linear-lanceolate to lanceolate, 3.5–7 mm; corolla 8–15 mm, tube and limb yellow, rarely white or cream, veins yellow to orangish yellow, rarely white; style 3.5–5 mm. Capsules ovoid, 2.2–4.5 × 2–3.5 mm. Seeds 0.4–0.6 mm. 2n = 28.
Phenology: Flowering May–Oct.
Habitat: Acidic freshwater pondshores, blackwater stream banks, cypress savannas, acidic wetlands, swamps.
Elevation: 0–300 m.
N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que., Conn., Del., D.C., Fla., Ga., Ill., Maine, Md., Mass., Mich., N.H., N.J., N.Y., N.C., N.Dak., Pa., R.I., S.C., Vt., Va., Wis., introduced in e Asia (Japan).
The name Gratiola aurea has been used widely for G. lutea due to questions about the applicability of the name by Rafinesque, which predates the name by Muhlenberg by two years. F. W. Pennell (1935) reviewed the nomenclatural history, noting that the type on which the name by Rafinesque is based, a collection by A. Michaux deposited at P, had been identified by A. Gray, M. L. Fernald, and S. F. Blake as G. neglecta. However, Pennell determined that the collection by Michaux was a mixed gathering and that the name by Rafinesque applies to the yellow-flowered element thereof.
Gratiola lutea (as G. aurea) has been reported from Crittenden County, Arkansas (W. H. Wilcox 1973); it is excluded from Arkansas in recent state checklists (E. B. Smith 1991; J. L. Gentry et al. 2013). Reports from Alabama may be based on misidentified specimens. A specimen identified as G. lutea has been collected in Japan (D. Estes 2008), where it was presumably introduced.