1. Stylophorum diphyllum (Michaux) Nuttall, Gen. N. Amer. Pl. 2: 7. 1818.
Celandine-poppy, mock poppy, yellow-poppy, wood-poppy
Chelidonium diphyllum Michaux, Fl. Bor.-Amer. 1: 309. 1803; Stylophorum ohiense Sprengel
Plants to 5 dm, downy. Stems simple or branching. Leaves to 5 dm; petiole to 2 dm; blade pale abaxially, deeply 5-7-lobed; margins irregularly dentate or crenate. Flowers: pedicels 25-80 mm; sepals ca. 15 mm; petals yellow, obovate, 2-3 cm wide; style 3-6 mm. Capsules ellipsoid, 20-35 mm, pubescent. Seeds pale brown, reticulate-pitted. 2 n = 20 (cult.).
Flowering spring. Moist deciduous woods, thickets, and cedar barrens, often on slopes, occasionally in fields or on shaded dunes, in loam or sand; 100-600 m; Ont.; Ala., Ark., Ill., Ind., Ky., Mich., Mo., Ohio, Tenn., Va., W.Va.
Vegetatively, this native species closely resembles the more frequent and widespread Chelidonium majus , introduced from Eurasia. Various authors have reported Stylophorum diphyllum from western Pennsylvania, but W. E. Buker and S. A. Thompson (1986) could not confirm its past or current native presence there.