Yellow marsh marigold is an aquatic or semi-aquatic plant, with rounded leaves and yellow flowers in the buttercup family (Ranunculaceae). If not floating, the stems are decumbent and rooting at nodes, 10-60 cm long. Leaves are rounded, often kidney-shaped, 2-20 cm wide. The margins are entire or crenate. Inflorescences are produced on upright stems, one to a few flowers grouped together. The large (2-5 cm across), open blossoms have five bright yellow tepals. Inside the flower there is a whorl of many yellow stamens and many short pistils. The fruits are follicles, which split open to release several seeds. The seeds are elliptic, 1.5-2.5 mm long. A few similar looking species of the genus Ranunculus can be found in similar amphibious habitats, but none have such large yellow flowers or broad, kidney-shaped leaves, while rooting at the stem nodes.
This species is perennial and flowers in early summer.
The flowers are bisexual, insect-pollinated and self-incompatible (Lundqvist 1992). The fruits are follicles, which split open to release several seeds. Seeds are dispersed via water. Plants can also spread vegetatively via rhizomes.
Plants contain protoanemonin and aconite, poisonous compounds. Tea brewed from Marsh Marigold leaves was used by the Yup'ik, to treat diarrhea or constipation (Lantis 1959 in Garibaldi 1999). To remove toxic compounds, water has to be changed two or three times (Jernigan et al. 2015).
Yellow marsh marigold has an incompletely circumpolar distribution, occurring across the northern hemisphere, except is absent from Greenland. Yellow marsh marigold occurs across Canada and the northern tier of U.S. states, reaching as far south as the mountains of California in the west and the Smoky Mtns. of North Carolina in the east. Caltha palustris occurs in wetlands across Alaska, and on both sides of the Alaska Range in Denali.