N.Vietnam, Cao Bang Prov., Trung Khanh Distr., Ngoc Khe Municipality, Pac Nga village, around point 22°54′59′'N, 106°31′44′'E, at elevation 800-850 m a.s.l.
Remnants of primary evergreen broad-leaved forest along tops of rocky ridges and mesae composed with light gray solid marble-like highly eroded crystalline limestone.
Treelet 3-4 m tall. Flowers light blue-violet. Very common. Co-dominant of 3 forest stratum.