1. Chelidonium majus Linnaeus, Sp. Pl. 1: 505. 1753.
Plants to 10 dm. Stems branching, ribbed. Leaves to 35 cm; petiole 2-10 cm; blade deeply 5-9-lobed; margins irregularly dentate or crenate, rarely laciniate. Inflorescences: peduncle 2-10 cm. Flowers: pedicels 5-35 mm; sepals to 1 cm; petals bright yellow, obovate to oblong, to 2 cm wide; style ca. 1 mm. Capsules linear to narrowly oblong, 2-5 cm, glabrous. Seeds black, reticulate-pitted.
Flowering spring-summer. Moist to dry woods, thickets, fields, hedgerows and fences, roadsides, railroads, and waste ground; 0-1000 m; introduced; B.C., N.B., N.S., Ont., P.E.I., Que.; Conn., Del., Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Utah, Vt., Va., Wash., W.Va., Wis.; Eurasia.
The irritating sap of Chelidonium has been used to treat warts. In the vegetative state, this weedy introduction from Eurasia is difficult to distinguish from the native Stylophorum diphyllum .