Paeonia obovata Maxim.

Pictures 2 to 5 in Japan, Honshu, Kitakata, June 2010
Picture 6 in Japan, Shikoku, Omogo, May 2008
Pictures 11, 12 & 13 : white form

Description in Mém. Acad. Imp. Sci. St.-Pétersbourg Divers Savans 9:29 (1859)