Shan Dou Gen

Sophora tonkinensis is a small evergreen shrub of the family Fabaceae, native to limestone hills and rocky slopes in southwestern China and northern Vietnam. The plant grows to roughly 1 to 2 meters tall, with finely pubescent young branches and pinnately compound leaves bearing 11 to 19 small elliptic to ovate leaflets that are gray-green and softly hairy beneath. Loose terminal racemes of pale yellow pea-like flowers appear in summer, followed by constricted, beaded legumes containing several seeds. The medicinal portion is the long, cylindrical, branched taproot and rhizome, harvested in autumn, woody and bitter, with a yellow-brown bark and pale yellow interior rich in quinolizidine alkaloids including matrine and oxymatrine. These alkaloids are responsible for both its therapeutic activity and its narrow safety margin.