Camellia sasanqua Thunb.

Family: Theaceae
English: Sasanqua
Japanese: サザンカ (山茶花) [Sazanka]

Compact leaves and large, open, white flowers that bloom and drop their petals in the fall. I find it interesting that the seed pods have not evolved to be large like the local camellias.

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）