Trollius paluster E.H.L.Krause Caltha palustris, known as marsh-marigold[1] and kingcup, is a small to medium sized perennial herbaceous plant of the buttercup family, native to marshes, fens, ditches and wet woodland in temperate regions of the Northern Hemisphere.

Caltha palustris is a 10–80 centimetres (4–31+1⁄2 in) high, hairless, fleshy, perennial, herbaceous plant that dies down in autumn and overwinters with buds near the surface of the marshy soil.

[2] The oldest description that is generally acknowledged in the botanical literature dates from 1700 under the name Populago by Joseph Pitton de Tournefort in part 1 of his Institutiones rei herbariae.

[3] The generic name Caltha is derived from the Ancient Greek κάλαθος (kálathos), meaning "goblet", and is said to refer to the shape of the flower.

It likes richer soils, but dislikes application of fertilizer and avoids high concentrations of phosphate and ammonium, and is also shy of brackish water.

The resulting insoluble mineral appears as "rusty" flocs on the water soil and the surface of the stems of marsh plants.

Around the edge of lakes and rivers it grows between reeds, and it can be found in black alder coppices and other regularly flooded and always moist forests.

[10] It is a component of purple moor grass and rush pastures – a type of Biodiversity Action Plan habitat in the UK.

Another visitor of Caltha palustris in western Europe is the leaf beetle Prasocuris phellandrii, which is black with four orange stripes and around ½ cm and eats the sepals.

[10] In the USA (Illinois) two species of leaf beetle can be found on Caltha: Plateumaris nitida and Hydrothassa vittata.

[13] In Canada, beetles (Cantharidae, Nitidulidae, Coccinellidae, Chrysomelidae, Cerambycidae), thrips (Thripidae), bugs (Miridae), butterflies (Pieridae), sawflies (Tenthredinidae), bees (Apidae, Halictidae, Andrenidae), ants (Formicidae) and flies (Sepsidae, Sciomyzidae, Ephydridae, Syrphidae, Anthomyiidae, Tachinidae and Muscidae) have been observed to visit the leaves or flowers, many of which were found carrying Caltha pollen.

Larger quantities of the plant may cause convulsions, burning of the throat, vomiting, bloody diarrhea, dizziness and fainting.

Small amounts of Caltha in hay do not cause problems when fed to husbandry, but larger quantities lead to gastric illness.

[20] Young leaves or buds should be submerged a few times in fresh boiling water until barely tender, cut into bite-sized pieces, lightly salted, and served with melted butter and vinegar.

[10] The common marsh marigold is planted as an ornamental throughout temperate regions in the world, and sometimes recommended for low maintenance wildlife gardens.