Twinleaf

Jeffersonia

Jeffersonia diphylla ( American Twinleaf )
A perennial, reaching a maximum size of 1.2 x 1.5 feet, that is native to rich woodlands in eastern North America ( from southeast Minn. to southern Wisconsin to central Michigan to Goderich, Ontario to Trenton, Ontario and New York State; south to northern Alabama to far northern Georgia ). In the Windsor/Essex County, Ontario region; it was abundant around Windsor, uncommon on the Lake Erie islands during the 1800s. It also occurred sporadically at Detroit and the Ohio shore during that time.
The leaves, up to 4 inches wide, are luxuriant mid-green above, bluish-white beneath.
The pure white flowers, up to 2 inches across, are borne during early spring.
Hardy zones 4 to 7 ( use local seed source in north ) in light to moderate shade on cool, humus-rich, well drained soil of average moisture. It is tolerant of alkaline soil and is rarely bothered by insects. Propagation is from seed or division done during early spring.

* USDA-NRCS PLANTS Database

* photos taken on May 7 2014 @ London Town Gardens, Edgewater, MD

* photo taken on Apr 24 2015 in Clarksville, MD

* photos taken on Apr 17 2016 @ U.S. National Arboretum, DC

Jeffersonia dubia ( Asian Twinleaf )
A rhizomatous perennial, that is similar to the above, except that it is native to deciduous forests of eastern Russia, northeast China and Korea.
The foliage is deep red at first, turning to deep green.
Hardy zones 4 to 7 ( likely also at least 3 )