Lysimachia hybrida is a perennial herb, to 1 m tall, colonial from a freely branching rhizome; stems erect, much-branched.
Leaves of winter rosette stalkless, or nearly so, stem leaves opposite, stalk hairy-fringed (ciliate) mostly below the middle; blade narrowly lance-shaped, 4-10 cm long, 1-2 cm wide, flat, tip pointed, base rounded to tapered, margin entire.
Flowers yellow, to 2.5 cm wide, radially symmetrical, petal lobes 0.6-1 cm long, 0.4-1 cm wide, base often reddish, widest above middle, margin ragged-toothed, abruptly pointed, spreading; calyx lobes narrow, 0.4-0.8 cm; blooms July-Aug.
Fruit dry, a capsule 0.4-0.6 cm wide; fruits Sept.-Oct. (Hough 1983).
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Swamp forests and marshes, wet soil.
Notes: Not actually a hybrid (Connecticut Wildflowers 2007).