Arisaema longipedunculatum M.Hotta var. yakumontanum Seriz.

Family: Araceae
Japanese: ヤクシマヒロハテンナンショウ [Yakushima Hiroha Tennanshō]

This species of "wide-leaf" arisaema is considered endangered and the yakushima variety—with limited— range is critically endangered. The flowers, which are usually green, look similar to the much more common A. japonica, but the leaves are broader and fewer.

References:
屋久島高地の植物 川原 勝征,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13日）
Tropicos.org. Missouri Botanical Garden. 05 Jun 2013 http://www.tropicos.org/Name/2106636 from Serizawa, Shunsuke. Acta Phytotaxonomica et Geobotanica 32(1-4): 27. 1981.