Lysimachia nummularia L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Creeping, often forming mats; lvs opposite, punctate, short-petioled, broadly quadrate to subrotund, 1–2.5 cm; fls solitary in the axils, the pedicels about equaling the lvs; cal-lobes foliaceous, triangular-ovate, 8 mm; cor-lobes 10–15 mm, dotted with dark red; 2n=32, 36, 43, 45. Native of Europe, escaped from cult. into moist places nearly throughout our range, often weedy. June–Aug.