Caltha palustris is a perennial herb, to 60 cm tall, poisonous when fresh. Contains an unstable oil, protoanemonin (Kingsbury 1964). Stems hollow, branched above.
Leaves alternate, broadly heart-shaped to kidney-shaped, base deeply lobed, with broad sinus, tip rounded, margin toothed, lower leaves long-stalked, upper becoming almost stalkless.
Flowers bright yellow, to 4 cm wide, sepals 5-9, petal-like, stamens numerous, April-June.
Fruit dry, clusters of dry narrow capsules to 1.5 cm long.
Wetland status: OBL.
Frequency in NYC: Infrequent.
Habitat: Along open streamsides, pond edges.
Notes: Sometimes confused with Ranunculus ficaria (lesser celandine), an upland, non-native, aggressively colonial plant.