Perennial herbaceous plant (Caltha palustris) of the buttercup family, native to wetlands in Europe and North America. It is grown in boggy wild gardens. The plant has a hollow stem, heart-shaped or round leaves, and glossy pink, white, or yellow flowers composed solely of sepals (petals are absent). The stems, leaves, and roots are sometimes cooked and eaten as a vegetable, though the fresh plant is poisonous. See alsocowslip.