Monotropastrum humile (D.Don) H.Hara

Family: Ericaceae
English: Indian pipe / Ghost pipe (sp.)
Japanese: ギンリョウソウ (銀竜草) [Ginryōsō]

This mysterious little flower is a parasitic plant that pops up in spring and early summer in mountainous regions across Japan, including Shiratani-Unsuikyo and along the route to Jomon Sugi at elevations aroun 600~900m.

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）