Houttuynia cordata Thunb.

in Nepal, Kathmandu Valley, june 2000 (picture 1)
in Sikkim, Pelling, july 2003 (picture 2)
in Japan, Honshu, Tokyo, June 2010 (pictures 3 & 4, with leaves of Iris)

Description in Fl. Jap. 234. t. 26