Rhododendron indicum (L.) Sweet

Family: Ericaceae
Japanese: サツキ (皐月) [Satsuki]

Starting in mid-May river boulders burn bright pink as the Satsuki azaleas burst into bloom. Later in the summer, the pink fire spreads to rocky mountain tops like Aiko Dake. However, don't confuse these with the similarly colored Yakushima Miyama azaleas, R. yakuinsulare, which are often mixed in with other shrubs and ferns on sunny mountain sides by the road. They bloom in the same season. Satsukis are popular with Japanese folks who remember sucking on the sweet flowers as children although many other azalea species are a bit toxic and I've never seen the monkeys take these. . .

References:
Tropicos.org. Missouri Botanical Garden. http://www.tropicos.org/Name/12302875 (4 June 2015)
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）