Stems erect, usually simple, 3-10 dm, usually sparsely pubescent, at least at nodes (or glabrous); rhizomes slender to somewhat thickened; bulblets absent. Leaves whorled; petiole absent or 0.1-0.3 cm, eciliate; blade elliptic to lanceolate or ovate, 3-12 : 0.8-3.5(-4.5) cm, base cuneate or rounded, slightly decurrent, margins entire, plane, glabrous or sometimes sparsely pubescent, apex acuminate or acute (rarely obtuse), surfaces densely to sparsely punctate, pubescent at least along abaxial veins and margins; venation pinnate-arcuate. Inflorescences axillary in leaves (distalmost axils sometimes without flowers), solitary flowers. Pedicels 1.5-3 cm, sparsely pubescent. Flowers: sepals 5, calyx streaked with dark resin canals, 3-6 mm, slightly stipitate-glandular, lobes lanceolate, margins thin; petals 5, corolla yellow with reddish base and, sometimes, margins, streaked with black or maroon resin canals, rotate, 5-8 mm, lobes with margins entire, apex acute to rounded, stipitate-glandular adaxially; filaments connate ca. 1.7 mm, shorter than corolla; staminodes absent. Capsules 3-3.5 mm, sometimes dark-punctate, glabrous. 2n = 84. Flowering summer. Dry to mesic hardwood forests, lowlands, fens, moist clearings, roadsides, and fields, rocky thickets and slopes, seashores; 0-1000 m; N.B., Ont., Que.; Ala., Conn., Del., D.C., Ga., Ill., Ind., Ky., Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis. A hybrid (known only from one population in Washington County, North Carolina) of Lysimachia quadrifolia with L. loomisii has been called L. ×radfordii H. E. Ahles.
Erect from long, stoloniform rhizomes, 3-9 dm, the stem glabrous or sparsely hairy, rarely branched; lvs in whorls of (3)4(-7), punctate, narrowly or broadly lanceolate, 5-10 cm, hairy beneath, widely spreading; fls axillary on spreading pedicels 2-5 cm, the upper half or two-thirds of the plant floriferous; cal-lobes lance-oblong, 2-4 mm; pet 6-8 mm, oblong or elliptic, yellow with dark lines; 2n=84. Moist or dry upland soil, chiefly in open woods; Me. to S.C., w. to Wis., e. Minn., Ill., Ky., and Ala.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.