Anemonopsis

Anemopsis californica ( Yerba Mansa )
A very rare perennial, reaching up to 3.5 x 2 feet, that is native to the western U.S. ( from Oregon to far western Kansas; south to southern California to western Texas ). It is the only species native to North America.
The very attractive, oblong leaves, up to 7 inches in length, are gray-green.
The white flowers are borne on upright spikes up to 2 inches in length, during late summer to mid autumn.
Hardy zones 4 to 8 in full sun on permanently moist to wet ( even shallow water ), fertile, humus-rich soil. It is tolerant of alkaline and saline soil but is not tolerant of drought.

Anemonopsis macrophylla
A very rare perennial, reaching up to 3.5 x 2 feet, that is native to mountain woodlands in Japan.
The very attractive, deeply-toothed, trifoliate leaves, up to 4 inches in length, are deep green.
The lavender flowers, up to 1.5 inches wide, are borne late summer to mid-autumn.
Hardy zones 4 to 8 in partial to full shade on moist, fertile, humus-rich soil. It is not drought tolerant.