Galium cf. kamtschaticum

Family: Rubiaceae
English: Boreal bedstraw
Japanese: ヤクシマムグラ (Yakushima mugura)

This species is distributed from Kamchatka to New England, and the Yakushima variety is considered endemic. However, I must admit that I'm not sure all these photos are of the same species: The last two are of a smaller plant with whiter flowers (perhaps even tinged pink) growing in restricted conditions among peat moss. The first three were larger plants with yellowish flowers growing in shaded dirt patches. Well, according to [la la teng shu, Chen Tao, & F. Ehrendorfer, Fl. China 19: 104?141. 2011], "Galium is by far the largest and most widespread genus within the tribe Rubieae."

(Galium cf. kamtschaticum var. minus, formerly Galium kamtschaticum var. yakusimense or Galium yakusimense. I hesitated to classify this as "less common", because it is very plentiful in some areas, but restricted to higher elevations, and perhaps certain species or varieties are less common than others.)

References:
屋久島高地の植物 川原 勝征,2001:南方新社.
la la teng shu, Chen Tao, & F. Ehrendorfer, Fl. China 19: 104-141. 2011.
米倉浩司・梶田忠 (2003-)　「BG Plants 和名－学名インデックス」（YList），http://bean.bio.chiba-u.jp/bgplants/ylist_main.html（2014年6月2日）.