Stems erect, simple, 3-8 dm, pubescent distally; rhizomes stout; bulblets absent. Leaves opposite to subopposite or whorled; petiole absent or 0.1-0.2(-0.4) cm, eciliate; blade lanceolate or linear-lanceolate to elliptic, 5-16 × 0.5-6 cm, base truncate to rounded or cuneate, not decurrent, margins entire, plane, eciliolate, apex acute to obtuse, surfaces punctate, glabrous or sometimes sparsely pubescent abaxially; venation pinnate. Inflorescences axillary, racemes, 1-3 cm. Pedicels 0.1-0.4 cm, stipitate-glandular or pubescent. Flowers: sepals 5-7(-9), calyx streaked with dark resin canals, 1-2.8 mm, glabrous, lobes narrowly lanceolate, margins thin; petals 5-7(-9), corolla light yellow, streaked with black or reddish-brown resin canals, somewhat funnelform, 3-7 mm, lobes with margins entire, apex rounded to acuminate, eglandular; filaments distinct or connate ca. 0.2 mm, nearly 2 times as long as corolla; staminodes absent (rarely staminodelike minute teeth present between fertile filaments). Capsules 2-3 mm, dark-punctate, glabrous. 2n = 40, 42, 54. Flowering spring-summer. Bogs, swamps, marshes, wet woods; 0-2000 m; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Utah, Vt., Wash., W.Va., Wis., Wyo.; Eurasia. Lysimachia thyrsiflora is known to hybridize readily with 17. L. terrestris (see discussion under the latter).
From Flora of Indiana (1940) by Charles C. Deam
In mucky or peaty soil in bogs and marshy places and less frequent in low, sandy borders of lakes. Usually found in shallow water. This species has been placed in another genus by some authors, assuming the presence of staminodia, but this character is not constant. (Rhodora 22: 193. 1920.) No doubt Andrews' report of this species from Monroe County should be referred to some species which occurs in that county, and which he has failed to report. This species is possibly restricted to the lake region of the state.
Erect, 3-7 dm, from long, stoloniform rhizomes; lvs punctate, narrowly lanceolate to linear, 5-12 cm; infl a few dense, short racemes 1-3 cm on spreading peduncles 2-4 cm arising from the middle axils; fls mostly 6-merous; cal-lobes narrowly lanceolate, 2.5 mm; cor-lobes linear, 4-5 mm, marked with black; stamens separate, erect, nearly twice as long as the pet; 2n=54. Swamps; circumboreal, s. to N.J., O. and Mo. (Naumburgia t.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.