Chionographis japonica Maxim. subsp. yakusimensis (Masam.) N.Tanaka

Family: Melanthiaceae
Japanese: ヤクシマシライトソウ (屋久島白糸草) [Yakushima Shiraitosō]

Lily often seen around Shiratani and growing from earthy mountain sides in the Exterior Mountains. The Yakushima subspecies/variety is smaller than typical C. japonica. (From what I can find, it seems that the name, Chionographis japonica var. yakushimensis used to apply to C. koidzumiana var. yakusimensis.)

References:
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）