Mitchella undulata Siebold et Zucc.

Family: Rubiaceae
Japanese: (ヒメ)ツルアリドオシ (蔓蟻通し) [Tsuru Aridōshi]

This petite vine receives its Japanese name from flowers and fruit that look similar to Damnicanthus indicus, and indeed these genuses are related [Wei-ping Huang et al, Molecular phylogenetics and biogeography of the eastern Asian–eastern North American disjunct Mitchella and its close relative Damnacanthus (Rubiaceae, Mitchelleae) ]. The flowers (which come in pairs that share a single ovary that will form a red berry) contain both male and female parts. However, close inspection reveals each plant has either 'pin' or 'thrum' type flowers that must be cross-pollinated with flowers of the other type! [F. Ganders. Fecundity in Distylous and Self-Incompatible Homostylous Plants of Mitchella repens (Rubiaceae)]

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14日）
Hayden, W. John. Partridge Berry: Simple Beauty Belies Complexity. Bulletin of the Virginia Native Plant Society 31, no. 1 (March 2012): 4 ,8. Retrieved 2016 from http://scholarship.richmond.edu/cgi/viewcontent.cgi?article=1138&context=biology-faculty-publications
F. Ganders. Fecundity in Distylous and Self-Incompatible Homostylous Plants of Mitchella repens (Rubiaceae). Evolution. Vol. 29, No. 1 (Mar., 1975), pp. 186-188. http://www.jstor.org/stable/2407152
Wei-ping Huang et al, Molecular phylogenetics and biogeography of the eastern Asian–eastern North American disjunct Mitchella and its close relative Damnacanthus (Rubiaceae, Mitchelleae). Botanical Journal of the Linnean. V 171(2):395–412, February 2013.