Blutaparon wrightii (Hook.f. ex Maxim.) Mears

Family: Amaranthaceae
Japanese: イソフサギ (磯塞) [Isofusagi]

I think it's amazing that this succulent and its frequent companion, Limonium wrightii, manage to grow so well on rocks that are often buried by waves.

Philoxerus wrightii (Gomphrenoideae) is a synonym.

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）