marsh marigold, perennial spring-blooming Old World and North American plant ( Caltha palustris ) of the family Ranunculaceae (buttercup family), found in wet places. It has rounded glossy leaves and large buttercuplike flowers of bright and shining yellow. The tops are reputed to be toxic but with boiling become edible and are often eaten as greens while young; the flower buds have been pickled and used as capers, and the flowers have been used for beverages. In the United States it is sometimes called cowslip. Other species of Caltha are also called marsh marigold. Marsh marigolds are classified in the division Magnoliophyta, class Magnoliopsida, order Ranunculales, family Ranunculaceae.