Celandine (Chelidonium majus)
Not related to the Lesser Celandine, this greater Celandine is a member of the poppy family that likes to grow at the edge of the woods. These plants were growing by one of the tufa bridges in Schenley Park, where they were blooming in the middle of May.
Gray describes the genus and the species:
CHELIDONIUM [Tourn.] L. CELANDINE. Sepals 2. Petals 4. Stamens 16-24. Style almost none; stigma 2-lobed. Pod linear-cylindric, smooth, 2-valved, the valves opening from the bottom upward. Seeds crested. —Biennial herb with brittle stems, saffron-colored acrid juice, pinnately divided or 2-pinnatifid and toothed or cut leaves, and small yellow flowers in a pedunculate umbel; buds nodding. (Ancient Greek name, from chelidon, the swallow, because its flowers appear with the swallows.)
С majus L.— Rich damp soil about towns, centr. Me. to Ont., and southw., common from s. Me. to Pa. May-Aug. (Nat. from Eu.)