Marsh Marigold

Caltha palustris
A perennial, reaching a size up to 2.3 x 2 feet, that is native to moist woods, swamps and marshes in North America ( from the Aleutian Islands and far northern Alaska to the Northwest Territories Islands to far northern Ontario to Newfoundland; south to Oregon to central Saskatchewan to Tennessee to North Carolina ). It is also found in Eurasia from Iceland to Siberia; south to Spain to Japan ). In the Windsor/Essex County, Ontario region; it occurred sporadically at Point Pelee and probably along Lake St Clair during the 1800s. It was abundant on the Ohio shore during that time.
The attractive, heart-shaped leaves, up to 5 x 7.5 inches wide, are glossy rich green. The Marsh Marigold goes dormant and disappears during summer. It is poisonous and should not be eaten, animals avoid it.
The glowing, golden-yellow, single, buttercup flowers, up to 2 inches across, are borne during early to mid spring.
Hardy zones 1 to 8 in partial to full shade on fertile, persistently moist to wet soil. Deer resistant.

* photos of unknown internet source

'Alba'
Compact and mounding in habit, with pure white flowers borne early spring.

'Plena'
Flowers are double and golden-yellow; otherwise similar.

Caltha polypetala
A perennial, reaching a size up to 2 x 2 feet, that is native to moist woods in Eurasia ( from Bulgaria to the Caucasus; south to Turkey to northern Iran ). It is similar to but larger growing than Caltha palustris.
The attractive foliage is glossy rich green. The leaves are up to 12 inches across.
The glowing, golden-yellow flowers, up to 3 inches across, are borne on dense clusters during early to mid spring.
Hardy zones 1 to 8 in partial to full shade on fertile, persistently moist to wet soil.