It flowers from July to September.
It is found in Guizhou and Yunnan provinces of China, growing on mountain slopes under Pinus forests or on open mountainsides, at around 1900 meters above sea level.
The inflorescence is terminal, racemose, with few flowers. Flowers are large, 18 mm long, on pedicels about 6 mm long, covered in short soft hairs. The calyx has 5 unequal sepals, one of which is hood-shaped and about 6 mm long, while the other two are elongated oval, approximately 4 mm long. The inner sepals are petaloid, elliptic-oblong, about 14 mm long and 6 mm wide, with 3-5 veins. Petals are 3, white or pale green-white, with lateral petals oblong, about 15 mm long, fused with the keel petal for about 2/3 of its length, and ending in 4 finger-like appendages.
Polygala dunniana differs from P. saxicola and P. koi in having smaller, elliptic to obovate or spoon-shaped leaves (10-15 mm long, 5-8 mm wide) covered with white transparent short stiff hairs near the leaf margin. Its inflorescence is very short with few large flowers (18 mm long), white or pale green-white in color, with the keel petal having 4 finger-like appendages.