Mitrastemon yamamotoi Makino

Family: Mitrastemonaceae
Japanese: ヤッコソウ (奴草) [Yakkosō]

A parasitic plant that feeds of the roots of trees in the beech family. After blooming in the fall, the male part of the flower (center in the above photo) falls off to reveal the female part (left and right) underneath.

References:
九州野山の花 片野田逸朗,2004：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）
http://parasiticplants.siu.edu/Mitrastemonaceae/