N. Vietnam, Hoa Binh prov., Da Bac distr., Cao Son municipality, Buoi Truong station near Ba Tri Mountain (20°52′31′'N, 105°11′48′'E). Secondary evergreen broad-leaved wet forest with bamboo on very steep shale slope along river. Forest on shale with quartzite at 500-550 m a.s.l. Terrestrial herb about 0.6 m on very steep shady slope. Flowers white with light violet tint. Not rare.