Hydrangea luteovenosa Koidz.

in Japan, Honshu, May 2008 (picture 1)
in Japan, Honshu, Kyoto, May 2008 (pictures 2, 3 & 4)
in Japan, Honshu, Mt. Fuji, May 2008 (picture 5)
in Japan, Honshu, Kobe, May 2008 (pictures 6 & 7)
in Japan, Honshu, Ofuna Botanical Garden, May 2008 (picture 8)

Description in Bot. Mag. (Tokyo) 1925, xxxix. 4