Hydrangea petiolaris Sieb. & Zucc.

in Japan, Honshu, Hibara Lake, June 2010 (pictures 1, 2, 3 & 4)
in Japan, Honshu, Mt. Fuji, May 2008 (picture 5)
in Japan, Honshu, Nikko, June 2010 (picture 6)
in Japan, Honshu, Senjogahara, June 2010 (picture 7)
in Japan, Honshu, Gomi Pond, June 2010 (pictures 8 & 9)
from S.Korea, Ullungdo, with bigger leaves ("var.megaphylla" pictures 10, 11, 12 & 13)