Caltha natans Pall.
Family: Ranunculaceae
floating marsh-marigold
Caltha natans image
William S. Alverson  
Etymology: Caltha: old Greek and later Latin name for the marigold or "chalice" or "cup"
Plants: perennial, floating aquatic with slender stems
Leaves: kidney-shaped to widely heart-shaped, not divided
Flowers: pink to white, 5-9-parted, 1/3" wide, petal-like sepals; blooms July-Aug.
Habitat: cold ponds, slowly moving streams
Conservation Status: Endangered