Hydrangea hydrangeoides (Siebold et Zucc.) B.Schulz

Family: Hydrangeaceae
English: Japanese hydrangea vine
Japanese: イワガラミ (岩絡み) [Iwagarami]

Creeping over boulders and up tree trunks in forests at higher elevations, the blooms are like profusions of pale, creamy-colored fireworks highlighted by solitary, tear-drop-shaped sepals. I also like the reddish leaf stems, similar to Hydrangea petiolaris, especially showy when the new leaves come out in spring. Formerly Schizophragma hydrangeoides.

References:
新版　屋久島の植物 川原勝征,初島住彦(監修),2001：南方新社
米倉浩司・梶田忠 (2003-)　「BG Plants 和名－学名インデックス」（YList），http://ylist.info（ 2019年8月14日）