Camellia japonica L. var. macrocarpa Masam.

Family: Theaceae
English: Japanese camellia or simply camellia
Japanese: リンゴツバキ (林檎椿) [Ringo Tsubaki] or ヤクシマツバキ [Yakushima Tsubaki]

Although camellias are usually loved for their large, early-blooming flowers (with sweet nectar that both white-eyes and monkeys love, Yakushima's camellias are known for their apple-sized seed pods that turn from granny-smith green to jona red and dwarf those of higher latitudes. The purpose is to keep native weevils from depositing eggs inside with a ~2cm-long probiscus.

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）