Stems erect, simple or branched, (1.2-)2-10 dm, glabrous; rhizomes slender; bulblets absent. Leaves opposite; petiole 0.1-0.5(-0.9) cm, ciliate at very base near nodes, cilia 0.1-0.8 mm; blade linear to narrowly lanceolate, 3.4-9 × 0.2-0.6 cm, base cuneate, decurrent, margins entire, revolute, eciliolate, apex acute to obtuse, surfaces not punctate, glabrous; venation single-veined or obscurely pinnate. Inflorescences axillary in distal leaves, solitary flowers (or verticils). Pedicels 0.5-2.8 cm, glabrous. Flowers: sepals 5, calyx not streaked, 3.5-6 mm, glabrous, lobes lanceolate, margins thickened; petals 5, corolla yellow, sparsely streaked with brownish-violet (sometimes obscure) resin canals, rotate, 7-13 mm, lobes with margins entire (sometimes slightly erose distally), glabrous, apex apiculate, stipitate-glandular adaxially; filaments weakly connate at very base, shorter than corolla; staminodes 0.6-0.9 mm. Capsules 3.5-5 mm, not punctate, glabrous (rarely sparsely stipitate-glandular). 2n = 34. Flowering summer. Moist prairies, meadows, roadsides, springs, swamps, bogs, other wetlands; 0-600 m; Man., Ont.; Ala., Ark., D.C., Ga., Ill., Ind., Iowa, Ky., Md., Mich., Minn., Mo., N.Y., N.Dak., Ohio, Okla., Pa., S.Dak., Tenn., Va., W.Va., Wis. Lysimachia quadriflora has been reported as an adventive from Massachusetts (B. A. Sorrie and P. Somers 1999).