A perennial in the buttercup family, Caltha leptosepala produces white spring flowers suited to persistently wet ground. It grows from a basal clump to about 0.3 m tall and favours full sun. Native to western North America, it flowers in the UK from March to May. It performs on heavy or light soils provided they remain wet.

White-flowered marsh marigold (Caltha leptosepala) is a 0.3 m perennial for wet, sunny spots that flowers from March to May.

https://en.wikipedia.org/wiki/Caltha_leptosepala

Caltha is a genus of rhizomatous perennial flowering plants in the family Ranunculaceae, to which ten species have been assigned. They occur in moist environments in temperate and cold regions of both the Northern and Southern Hemispheres.

Caltha leptosepala

White-flowered marsh marigold | Caltha leptosepala

Caltha minor is a rhizomatous perennial in the buttercup family that bears star-shaped flowers in March to May. It favours moist habitats and produces heart- or kidney-shaped leaves. The blooms have no true petals; their coloured sepals — yellow to white — provide the floral display. Plants spread by short rhizomes to form low clumps.

Kingcup (Caltha minor) is a rhizomatous buttercup that favours moist ground and flowers from March to May.

Caltha minor

Kingcup | Caltha minor

Caltha palustris is a perennial herbaceous plant that favours wet ground and produces its main display early in the year. It suits full sun and tolerates a range of soils from sandy to clay so long as they remain moist. Mature plants grow to about 0.3 m. Flowering is concentrated from March to May in the UK.

Marsh marigold (Caltha palustris) flowers from March to May and suits wet, sunny sites on sandy to clay soils in temperate UK gardens.

https://en.wikipedia.org/wiki/Caltha_palustris

Caltha palustris

Marsh marigold | Caltha palustris

Caltha palustris 'Alba' is a perennial herbaceous member of the Ranunculaceae that produces white spring flowers. It grows to roughly 0.3 m and prefers consistently wet soils. The plant suits full sun and tolerates sandy, loamy or clay substrates when moisture is high.

White marsh marigold (Caltha palustris 'Alba') has white spring flowers in March–May and prefers wet soils and full sun at pond margins.

Caltha palustris 'Alba'

White marsh marigold | Caltha palustris 'Alba'

Caltha palustris 'Flore Pleno' is a perennial in the ranunculus family grown for its early-season flowering. It reaches about 0.3 m and prefers consistently wet soils. Give it a sunny position in sandy, loamy or clay ground and it will tolerate UK winters as a fully hardy plant. Its flowering period in the UK runs from March to May.

Marsh Marigold 'Flore Pleno' thrives in wet, sandy to clay soils in full sun and flowers in the UK from March to May.

Caltha palustris 'Flore Pleno'

Marsh Marigold 'Flore Pleno' | Caltha palustris 'Flore Pleno'

Caltha palustris 'Multiplex' is a herbaceous perennial in the Ranunculaceae grown for its spring flowering and preference for wet ground. It forms a low clump to about 0.3 m. Plant it in full sun into consistently wet soil types, including sandy, loamy or clay. Flowering in the UK occurs from March to May.

Double Marsh Marigold (Caltha palustris 'Multiplex') is a fully hardy, low perennial for wet, sunny sites, flowering in the UK from March to May.

Caltha palustris 'Multiplex'

Double Marsh Marigold | Caltha palustris 'Multiplex'

Caltha polypetala is a perennial in the buttercup family adapted to persist in wet, marshy ground. It grows where soil remains moist and benefits from humus-rich conditions. Place it in full sun to partial shade at pond margins or in bog gardens. It flowers from March to May, providing an early-season presence in wetland planting.

Giant marsh marigold (Caltha polypetala) thrives in wet, humus-rich soil at pond edges and flowers from March to May.