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 .
From Flora of Indiana (1940) by Charles C. Deam
Three authors have reported this species as escaping from about dwellings. I found it in moist woods in De Kalb and Lagrange Counties where it formed a dense stand over acres. In the other counties where I found it only a few plants were found at a place. I predict that where this species becomes established in woodland, it will be the principal part of the spring flora. This plant was formerly used in medicine but is no longer official. This use is, no doubt, responsible for its cultivation and escape.
Branched, 3-8 dm; cauline lvs several, alternate, much like those of Stylophorum diphyllum; sep glabrous; pet 1 cm; fr 3-5 cm; 2n=12. Eurasian sp., well established in moist soil from Que. to Io., s. to Ga. and Mo. Apr.-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.